Biostatistics Assignment
Two Paper is attached below. Choose 1 paper. Read it carefully.
Identify the main independent and dependent variables.
Identify the statistical hypotheses that have been tested in this article.
What statistical tests have been used to test those hypotheses?
Which of those tests are statistically significant?
What can you say about the practical importance of the results?
Summarize your responses in a two page double spaced typed paper. The grading of the paper will be done using the following rubric:
Style issues (20 points)
- APA Style references (with close attention to comma, space, period etc.) (5 points)
- Correct grammar (5 points)
- Correct spelling (5 points)
- Adherence to the specified page limit (5 points)
Content issues (80 points)
- Correct identification of independent and dependent variables (20 points)
- Correct description of statistical hypotheses (15 points)
- Correct identification of statistical tests (15 points)
- Correct interpretation of statistical tests (15 points)
- Correct interpretation of practical importance (15 points)
APPLIED AND ENVIRONMENTAL MICROBIOLOGY, June 2006, p. 4239–4244 Vol. 72, No. 6
0099-2240/06/$08.00�0 doi:10.1128/AEM.02532-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Use of Copper Cast Alloys To Control Escherichia coli O157
Cross-Contamination during Food Processing
J. O. Noyce,1* H. Michels,2 and C. W. Keevil1
Environmental Healthcare Unit, University of Southampton, Biomedical Sciences Building, Bassett Crescent East, Southampton
SO16 7PX, United Kingdom,1 and Copper Development Association Inc., 260 Madison Avenue, New York, New York 100162
Received 27 October 2005/Accepted 24 March 2006
The most notable method of infection from Escherichia coli O157 (E. coli O157) is through contaminated food
products, usually ground beef. The objective of this study was to evaluate seven cast copper alloys (61 to 95%
Cu) for their ability to reduce the viability of E. coli O157, mixed with or without ground beef juice, and to
compare these results to those for stainless steel. E. coli O157 (NCTC 12900) (2 � 107 CFU) mixed with
extracted beef juice (25%) was inoculated onto coupons of each copper cast alloy or stainless steel and
incubated at either 22°C or 4°C for up to 6 h. E. coli O157 viability was determined by plate counts in addition
to staining in situ with the respiratory indicator fluorochrome 5-cyano-2,3-ditolyl tetrazolium. Without beef
extract, three alloys completely killed the inoculum during the 6-h exposure at 22°C. At 4°C, only the
high-copper alloys (>85%) significantly reduced the numbers of O157. With beef juice, only one alloy (95% Cu)
completely killed the inoculum at 22°C. For stainless steel, no significant reduction in cell numbers occurred.
At 4°C, only alloys C83300 (93% Cu) and C87300 (95% Cu) significantly reduced the numbers of E. coli O157,
with 1.5- and 5-log kills, respectively. Reducing the inoculum to 103 CFU resulted in a complete kill for all seven
cast copper alloys in 20 min or less at 22°C. These results clearly demonstrate the antimicrobial properties of
cast copper alloys with regard to E. coli O157, and consequently these alloys have the potential to aid in food
safety.
Escherichia coli O157:H7 has emerged as a serious food-
borne pathogen, with outbreaks associated primarily with con-
sumption of undercooked ground beef (17), although other
transmission routes exist, including potable (19) and recre-
ational water (1). The bacterium was first identified as a patho-
gen in 1982, and the numbers of cases reportedly caused by this
strain have increased over the last decade in many countries
(18). The physiological effects of E. coli O157:H7 infection
range from diarrhea (2% of all cases in the western world) to
serious and life-threatening conditions, including hemorrhagic
colitis, hemolytic uremic syndrome, and thrombotic thrombo-
cytopenic purpura (6). A recent outbreak (September 2005) in
southern Wales resulted in 157 cases over a period of 20 days,
with 65% affecting school age children and one unfortunate
fatality in a 5-year-old male. Evidence to date traced the source
to a supplier of cooked meats to a school meals service (9).
The intestinal tract of cattle is considered the major reser-
voir of E. coli O157 (2), and the contamination with beef is
attributed to contact with feces from the ruptured gut, hide,
hair, or hooves of the animals during the slaughter process
(10). Once contaminated, subsequent downstream processing
can potentially lead to cross-contamination from the meat to
any point of contact. The metal of choice for food preparation
and handling is stainless steel (types 304 and 316) due to its
mechanical strength, corrosion resistance, longevity, and ease
of fabrication (11). However, it has been shown that even with
cleaning and sanitation procedures consistent with good man-
ufacturing practices, microorganisms can remain in a viable
state on stainless steel equipment surfaces (14). In addition,
this alloy has been shown to be ineffective at reducing micro-
bial load once it is contaminated. A study conducted by
Kusumaningrum et al. demonstrated that Salmonella enteriti-
dis, Staphylococcus aureus, and Campylobacter jejuni remained
viable on dry stainless steel surfaces for many hours after
inoculation (13), which raises the issue of alternative materials
for surfaces in food-processing environments. Pure copper and
copper-containing alloys such as brass and bronze have the
potential to control microbial populations due to the well-
documented antimicrobial properties of copper itself (4, 7, 8,
15, 16). With this in mind, a selection of the most widely used
cast copper alloys (including brasses, bronzes, and copper-
nickel-zinc) were tested for their ability to reduce the viability
of E. coli O157 cultured in a high-protein (50%) medium,
tryptone soy broth (TSB), with or without the addition of beef
liquid (to reflect the presence of meat residue during process-
ing) extracted from minced beef (19% protein, 26% fat con-
tent), with results compared to those for food-grade stainless
steel.
MATERIALS AND METHODS
Preparation of E. coli O157 cultures. E. coli O157 (NCTC 12900) was main-
tained on glycerol protect beads (Fisher Scientific, United Kingdom) at �80°C.
For experimental tests, 15 ml of TSB was aseptically inoculated with a single
bead and incubated at 37°C for 16 h. After this incubation period, the culture
contained �1.25 � 109 CFU per ml. Unless otherwise stated, media were
obtained from Oxoid (Basingstoke, Hampshire, United Kingdom).
Preparation of liquid beef extract. Minced beef (500 g; 19% protein, 26% fat)
was purchased from a leading United Kingdom supermarket and stored in bags
(50-g amounts) at �20°C until required, and then they were defrosted and stored
* Corresponding author. Mailing address: Environmental Health-
care Unit, University of Southampton, Biomedical Sciences Building,
Bassett Crescent East, Southampton SO16 7PX, United Kingdom.
Phone: 44 2380 592034. Fax: 44 2380 594459. E-mail: J.O.Noyce
@Soton.ac.uk.
4239
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at 4°C. For experimental procedures, a 20-ml sterile syringe housing was modi-
fied by the addition of a series of small holes to the top end of the tube using a
syringe needle. The syringe tube was then filled approximately one third (9 �
0.9 g) with beef mince, and the plunger was reinserted into the syringe housing.
Pressure was then applied to the mince, and the liquid extract that appeared
from the holes was removed with a sterile pipette tip and transferred to a 1.5-ml
Eppendorf tube. The liquid extract was stored at 4°C and used on the day of
production. Microbial contamination of the beef extract was determined by
serially diluting the juice in sterile phosphate-buffered saline (PBS) and plating
out on nutrient agar plates. The CFU count detected from all meat samples
used was 0.
Preparation of alloy coupons. Table 1 lists the compositions of the alloys
tested during this study. Sample ingot blocks (1 cm by 1 cm by 1 cm) of each
metal type (provided by the Copper Development Association, New York, NY)
were cut into sections (3 mm thickness) and then into small coupons (1 cm by 1
cm by 0.3 cm). Prior to testing, these coupons were degreased and cleaned by
vortexing for 30 s in 10 ml acetone containing �30 2-mm-diameter glass beads
(Merck, United Kingdom). After cleaning, coupons were immersed in ethanol
and flamed in a Bunsen burner before being transferred to a sterile plastic
container with a lid to prevent contamination prior to inoculation. Coupons
remained within the container during the experimental procedures.
Alloy testing. For experiments testing the effect of meat residue, liquid beef
extract (100 �l) was added to 300 �l of E. coli culture and gently mixed by
pipetting. Coupons were aseptically inoculated with either 20 �l of E. coli-beef
extract suspension (2 � 107 CFU) or E. coli culture (2.7 � 107 CFU) alone.
Droplets were spread evenly across the whole surface of the coupon using a
separate sterile pipette tip. Following inoculation, the coupons were incubated at
either room temperature (22 °C � 2°C) or 4°C (to represent cold storage areas)
for varying time periods, ranging from 15 min to 6 h. Control coupons were
removed immediately after inoculation at time zero to determine the initial
number of viable bacterial cells. Relative humidity in the laboratory was moni-
tored and recorded (50% � 10%). The effect of desiccation on the viability of E.
coli O157 with or without beef extract over 6 h was investigated, and no effect was
seen (data are from stainless steel coupons). Mean drying time at room temper-
ature for the evenly spread 20-�l droplet was 65 min (�7 min) for all the cast
alloys tested (with or without beef extract).
After incubation, cells were removed from the coupons by vortexing for 30 s in
10 ml sterile PBS containing �20 2-mm glass beads. The effect of copper release
into the PBS on the viability of recovered cells (measured in CFU) was investi-
gated by the addition of 20 mM EDTA, which readily complexes free copper
(20). No significant difference was seen in the number of colonies formed (data
not shown) between samples recovered into PBS or PBS with EDTA. Thorough
analysis of coupons by episcopic differential interference contrast (EDIC) mi-
croscopy revealed no attached cells after washing (12). To ascertain the number
of viable cells removed from the coupons, 100 �l was removed and serially
diluted to 10�4 in sterile PBS. Nutrient agar plates were then inoculated with 50
�l of each dilution, which was spread evenly over the surface of the agar with a
sterile, glass spreader. This provided a detection limit of 200 CFU, although
subsequent analysis using a viability stain (see the next section on reduced
inoculum testing) confirmed zero counts when they occurred. Postinoculation,
plates were incubated at 37°C for 18 h, and the number of CFU was counted and
used to calculate the number of viable CFU per coupon. Three plates were
completed for each dilution, and the means were calculated. Three replicates
were completed for each alloy sample as well as for each time period and
temperature regime.
Reduced inoculum testing. Contamination of a work surface of 107 CFU cm�2
would represent a significant breakdown in hygiene practices. Contamination by
E. coli O157 of beef carcasses and boned head meat after slaughter was found at
concentrations of 1.41 log10 CFU g
�1 and 1.0 log10 CFU g
�1, respectively (5).
Consequently, contamination of food-processing surfaces would be significantly
less than 107 CFU cm�2. To determine the effect of a reduced inoculum size on
the time required for total kill on each of the cast alloys and stainless steel, the
number of E. coli O157 cells inoculated onto sample coupons was reduced by
serially diluting the original cell culture-beef extract solution. Four serial 1:10
dilutions were performed, and sample coupons were inoculated with 20 �l of the
final dilution (103 CFU). Tests were conducted at room temperature (22 °C �
2°C), and samples taken every 10 min up to a period of 30 min. After
exposure, coupons were transferred to tubes containing 2 ml sterile PBS
(detection limit of 40 CFU) with glass beads and then were treated as
described above for alloy testing. Zero counts were additionally confirmed by
viability staining in situ on the metal surfaces with 5-cyano-2,3-ditolyl tetra-
zolium (CTC), as described below.
Episcopic differential interference contrast (EDIC) and epifluorescent mi-
croscopy analysis. To confirm results obtained from the direct culturing of CFU
recovered from sample coupons in addition to investigating the possibility of the
presence of sublethally damaged or viable but nonculturable cells, images were
taken of inoculated coupons by both EDIC and epifluorescent microscopy. For
the epifluorescent analysis, E. coli cells on inoculated coupons were stained with
5-cyano-2,3-ditolyl tetrazolium (CTC), which detects actively respiring bacteria
(3). Coupons were flamed first and then inoculated with 20 �l of beef extract-E.
coli culture as described in the alloy testing protocol. Only metal samples which
produced zero viable cell counts were tested. For stainless steel, sample coupons
were analyzed after an exposure period of 6 h. After the exposure period,
coupons were transferred to 55-mm petri dishes, and 50 �l of 10 mM CTC was
added to the surface and incubated in the dark for 4 h. Postincubation, the
coupons were thoroughly examined using an EDIC/epifluorescent microscope
(Nikon Eclipse Model ME600; Best Scientific, Swindon, United Kingdom)
equipped with a �40 objective and epifluorescent filters appropriate for CTC.
For each coupon tested, representative EDIC and epifluorescent pictures were
taken using a digital camera (Model CoolSnap CF; Roper Industries, United
Kingdom) connected to a personal computer with digital image analysis software
(Image-Pro Plus, version 4.5.1.22; Media Cybernetics, United Kingdom).
Statistical analysis. Data are expressed as the means � standard errors of the
means (SEM). For group comparison, a Mann-Whitney U test was used. Statis-
tical significance was defined as P � 0.05. Statistical procedures were performed
using SigmaStat version 2.03, and graphical analyses were performed with
SigmaPlot version 8.0.
RESULTS
E. coli viability on copper cast alloys and stainless steel. The
effect of E. coli O157 viability on exposure to stainless steel or
copper cast alloys at either 22°C or 4°C without the presence of
beef extract can be seen in Fig. 1 and 2, respectively. From Fig.
1 it is evident that exposure to stainless steel for 6 h at 22°C had
no significant effect (P � 0.05) on the mean number of CFU
per coupon. At time zero, the mean number of viable CFU per
coupon was 2.7 � 107, with 1.7 � 107 CFU coupon�1 remain-
ing after 6 h. What is also clear from Fig. 1 is that the percent-
age of copper content of the cast alloys is not directly linked to
their ability to reduce viability of E. coli O157. Of the seven
cast alloys tested, three reduced the inoculum CFU to 0 (�7-
log kill) within the exposure period of 6 h: C87300 (95% Cu),
C83600 (85% Cu), and C83300 (93% Cu). For alloy C87300, a
significant 4-log reduction was achieved in only 45 min, with no
viable E. coli organisms remaining after 75 min. However, alloy
C83600 completely killed the inoculum in 3 h, compared to
4.5 h for alloy C83300, which actually contained a higher cop-
per content (8% higher). In addition, alloy C95500 (78% cop-
per content) demonstrated no significant reduction (P � 0.05)
in the numbers of cells recovered after 6 h compared to those
of control coupons at time zero. Comparison between C97600
TABLE 1. Metal samples and their constituent components
Metal type
UNSa
no.
% Composition
Cu Al Zn Sn Ni Pb Mn Fe Si
Silicon bronze C87300 95 1 1
Red brass C83300 93 4 1.5 1.5
Brass C83600 85 5 5 5
Ni-Al bronze C95800 81 9 5 1 4
Al bronze C95500 78 11 4 3 4
Ni sliver C97600 66 6 4 20 4
Yellow brass C85700 61 37 1 1
Stainless steel 304b S30400 10 2 65.45 1
a UNS, Unified Numbering System.
b Stainless steel 304 also contains 0.8% C, 20% Cr, 0.45% P, and 0.3% S.
4240 NOYCE ET AL. APPL. ENVIRON. MICROBIOL.
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and alloys C95800 and C85700 at 6 h revealed a significant
difference (P � 0.05) in the numbers of E. coli killed. At 6 h,
the mean number of viable E. coli cells remaining on alloy
C97600 was 333 CFU, compared to 2,567 and 2,300 CFU for
alloys C95800 and C85700, respectively.
The effect on E. coli O157 viability at 4°C is shown in Fig. 2.
Of the alloys tested, C87300 (95% Cu), C83600 (85% Cu), and
C83300 (93% Cu) were the only ones which demonstrated an
effect on E. coli viability, with all three completely killing the
107-CFU inoculum in 3 h. However, it must be noted that for
alloy C83300, the complete kill of the inoculum was faster at
4°C than at 22°C, a pattern which is the reverse for all the other
alloys. After 3 h at 22°C, a mean number of 267 viable cells
remain on alloy C83300, with this diminishing to zero at 4.5 h.
This reverse trend can be attributed to a single isolated repli-
cate where viable cells were recovered. All other replicates for
this alloy after 3 h at room temperature resulted in no recovery
of viable cells. Additional replicates (n 3) (data not shown)
have also resulted in total kill of the inoculum for this time
point and temperature regimen, which indicates that the kill
rate at room temperature is in fact faster than that at 4°C for
alloy C83300. Viability for the four remaining copper alloys
and stainless steel remained unaffected for E. coli O157, with
no significant difference in cell numbers at 6 h compared to
that at time zero.
The effect of the addition of the liquid beef extract on
exposure to stainless steel or copper cast alloys on E. coli O157
viability at either 22°C or 4°C can be seen in Fig. 3 and 4,
respectively. From Fig. 3, it can be seen that once again expo-
sure to stainless steel for 6 h at 22°C had no significant effect
(P � 0.05) on the mean number of CFU per coupon. What is
also immediately clear is the reduced antimicrobial activity for
all the alloys to which beef juice had been added. Of the seven
cast alloys tested, only one reduced the inoculum CFU to zero,
C87300 (95% Cu), with complete kill achieved after 90 min, a
result previously accomplished after 75 min. For alloy C83300
(93% Cu) with beef extract, a significant (P � 0.05) 5-log kill
was achieved after 6 h, compared to complete kill in under 6 h
with no beef extract. Both alloys C85700 (61% Cu) and C83600
FIG. 1. Effect on E. coli O157 viability of a 6-h exposure to either
stainless steel (�), C873000 (�), C83600 (Œ), C83300 (�), C97600
(}), C95800 (F), C85700 (‚), or C95500 (■) at 22°C. Coupons (1 cm
by 1 cm) were inoculated with 20 �l of a 19-h E. coli O157 culture.
Following the exposure period, coupons were transferred to tubes
containing 10 ml sterile PBS with 2-mm-diameter glass beads. Cells
were subsequently removed from the coupons into suspension by vor-
texing, and 100 �l was removed and serially diluted to 10�4 in sterile
PBS. TSB plates were then inoculated (50 �l) for each dilution and
subsequently incubated at 37°C for 18 h. Postincubation, the number
of CFU on each plate was counted and used to calculate the number
of viable CFU per coupon. Points represent the means (n 3) � SEM.
FIG. 2. Effect on E. coli O157 viability of a 6-h exposure to either
stainless steel (�), C873000 (�), C83600 (Œ), C83300 (�), C97600
(}), C95800 (F), C85700 (‚), or C95500 (■) at 4°C. Coupons (1 cm by
1 cm) were inoculated with 20 �l of a 19-h E. coli O157 culture.
Following the exposure period, coupons were transferred to tubes
containing 10 ml sterile PBS with 2-mm-diameter glass beads. Cells
were subsequently removed from the coupons into suspension by vor-
texing, and 100 �l was removed and serially diluted to 10�4 in sterile
PBS. TSB plates were then inoculated (50 �l) for each dilution and
subsequently incubated at 37°C for 18 h. Postincubation, the number
of CFU on each plate was counted and used to calculate the number
of viable CFU per coupon. Points represent the means (n 3) � SEM.
FIG. 3. Effect on E. coli O157 viability of a 6-h exposure to either
stainless steel (�), C873000 (�), C83600 (Œ), C83300 (�), C97600
(}), C95800 (F), C85700 (‚), or C95500 (■) at 22°C in the presence
of liquid beef extract. Coupons (1 cm by 1 cm) were inoculated with 20
�l of a 19-h E. coli O157 culture. Following the exposure period,
coupons were transferred to tubes containing 10 ml sterile PBS with
2-mm-diameter glass beads. Cells were subsequently removed from the
coupons into suspension by vortexing, and 100 �l was removed and
serially diluted to 10�4 in sterile PBS. TSB plates were then inoculated
(50 �l) for each dilution and subsequently incubated at 37°C for 18 h.
Postincubation, the number of CFU on each plate was counted and
used to calculate the number of viable CFU per coupon. Points rep-
resent the means (n 3) � SEM.
VOL. 72, 2006 E. COLI O157 CROSS-CONTAMINATION ON COPPER 4241
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(85% Cu) achieved 3-log kills, with mean CFU of 7,867 and
10,000, respectively, remaining viable at 6 h. Nearly identical
kill rates were observed, even with a difference in total copper
content of the alloys of 24%. Both C95800 (81% Cu) and
C95500 (78%) at 6 h produced 1-log reductions in the viability
of E. coli O157, although alloy C97600 with a lower copper
content of 66% produced a significant (P � 0.05) 2-log kill.
The effect of added beef juice on E. coli O157 viability at 4°C
is shown in Fig. 4. For clarity, in the figure only plots for alloys
C87300, C83300, C83600, and stainless steel have been shown.
As previously shown at room temperature, antibacterial activ-
ity is reduced. From the alloys tested, only C87300 (95% Cu)
and C83300 (93% Cu) demonstrated significant (P � 0.05)
antimicrobial ability on E. coli at chill temperatures, with 5 and
1.5-log kills, respectively. Viability for the five remaining cop-
per alloys and stainless steel remained unaffected for E. coli
O157, with no significant difference (P � 0.05) in cell numbers
at 6 h compared to that at time zero.
The effect on total kill time of reducing the inoculum size of
E. coli O157 when exposed to the seven cast copper alloys can
be seen in Fig. 5. Reducing the number of CFU to 103 resulted
in complete kill for all the alloys tested in 20 min or less. Once
again, viability on stainless steel remained unaffected at the
30-min time point. For three of the copper alloys, C87300,
C83300, and C83600, complete kill was achieved in 10 min.
Epifluorescent microscopy and digital image analysis. To
confirm that the low numbers of cells recovered on the copper
alloys was indeed due to cell death, epifluorescent images were
taken of sample coupons stained with CTC before cells were
due to be removed for culture. The images of cells at time zero
on either copper alloys or stainless steel indicated active res-
piration, shown by the numerous points of red emission within
the images due to the intracellular reduction of CTC to the
water-insoluble fluorescent product 3-cyan-1,5-di-tolyl-forma-
zan (data not shown). Subsequently, by contrast, there was no
fluorescent labeling of cells incubated on the copper surfaces
where no subsequent culture could be obtained. The EDIC
microscopy images showed that the cells were still present but
not respiring. In contrast, images of inoculated stainless steel
after 6 h of incubation at 22°C clearly show the presence of
respiring cells whose numbers matched the culturable numbers
of cells recovered on the agar medium.
DISCUSSION
Infections from E. coli O157 are serious and life threatening,
with contamination of ground beef representing a significant
source. Preparation of meat products requires surfaces that are
resilient and easily cleaned to reduce the risk of contamination.
Stainless steel, although hard wearing and easily cleaned, is not
intrinsically effective at reducing numbers of viable bacteria,
which suggests that food-processing environments would ben-
efit from the installation of materials that are inherently bio-
cidal.
The data from this study demonstrate that the viability of the
pathogen E. coli O157 can be significantly affected by three
factors: the composition of the substrate alloy on which it is
placed, the ambient temperature, and the presence of beef
juice. The addition of the liquid beef extract in these tests was
used to represent soiling of preparation surfaces, although
regular cleaning as part of any normal hygiene policy should
normally prevent contact areas from becoming this dirty, i.e.,
meat residue allowed to remain on a surface for up to 6 h. With
regards to the metal of choice, E. coli O157 was able to persist
in a viable state in dried deposits on stainless steel at room
temperature for periods of 6 h regardless of whether beef juice
FIG. 4. Effect on E. coli O157 viability of a 6-h exposure to either
stainless steel (�), C873000 (�), C83600 (Œ), or C83300 (�) at 4°C in
the presence of liquid beef extract. Coupons (1 cm by 1 cm) were
inoculated with 20 �l of a 19-h E. coli O157 culture mixed with liquid
beef extract (25%). Following the exposure period, coupons were
transferred to tubes containing 10 ml sterile PBS with 2-mm-diameter
glass beads. Cells were subsequently removed from the coupons into
suspension by vortexing, and 100 �l was removed and serially diluted
to 10�4 in sterile PBS. TSB plates were then inoculated (50 �l) for
each dilution and subsequently incubated at 37°C for 18 h. Postincu-
bation, the number of CFU on each plate was counted and used to
calculate the number of viable CFU per coupon. Points represent the
means (n 3) � SEM.
FIG. 5. Effect of reduced inoculum size on time for total kill when
exposed to copper cast alloys C873000 (�), C83600 (Œ), C83300 (�),
C97600 (}), C95800 (F), C85700 (‚), or C95500 (■) or stainless steel
(�) at 22°C. Coupons (1 cm by 1 cm) were inoculated with 20 �l of a
serially diluted E. coli culture-liquid beef extract solution (103 CFU).
Following the exposure period, coupons were transferred to tubes
containing 10 ml sterile PBS with 2-mm-diameter glass beads and
vortexed for 30 s, and 50 �l was removed and TSB plates inoculated,
followed by incubation at 37°C for 18 h. Postincubation, the number of
CFU on each plate was counted and used to calculate the number of
viable CFU per coupon. Points represent the means (n 3) � SEM.
4242 NOYCE ET AL. APPL. ENVIRON. MICROBIOL.
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was present. In contrast, survival on the high-copper alloy
C87300, for example, was significantly reduced, with complete
kill of 107 cells achieved after 75 min without beef extract and
in 90 min even with the beef juice.
Also apparent is the effect of temperature on antimicrobial
activity. Reducing the exposure temperature to 4°C increased
the time required to totally kill the inoculum on the cast copper
alloys which had previously achieved this at 22°C. Further
reductions in antimicrobial activity were found with the addi-
tion of the liquid beef extract. For example, only two alloys,
C87300 and C83300, with mean CFU counts at 6 h of 133 and
4.7 � 105, respectively, showed any effect on cell viability. For
the remaining five cast copper alloys, antimicrobial activity was
effectively removed at chill temperatures, which in turn sug-
gests that alloys with �90% copper should be utilized under
these conditions to provide significant disinfection ability.
What is clear, though, is the significantly faster and greater
kill rates on the high-copper cast alloys (�80%) without the
addition of liquid beef extract, which suggests that the extract
itself provides a protective matrix for the bacterial cells to
“hide in” from the detrimental effects of copper exposure. This
may be due to the fat content, since the raw minced beef
contained 26% fat before the juice was extracted. What these
findings also suggest is that copper-based work surfaces that
are free from meat residue would be even more effective at
reducing microbial load if contamination occurs. However, as
shown from the results presented here, significant reductions
in viability are still achieved with the presence of a “meat
residue.” In addition, results from the reduced inoculum tests,
representing possible levels of processing contamination, show
rapid disinfection for all the copper alloys sampled, with four
achieving this in 20 min and the remaining three (with the
highest copper content) in only 10 min.
In addition, reducing the copper content in the alloys tested
in general reduced the numbers of E. coli O157 cells killed,
although this was not the case for all alloys. In particular, the
aluminum-bronze alloy C95500 (11% Al, 78% Cu) and the
nickel-aluminum-bronze alloy C95800 (9% Al, 81% Cu) both
demonstrated poor antimicrobial ability regardless of the pres-
ence of beef residue. This lack of antimicrobial property from
these high-copper alloys could be attributed to the formation
of a protective aluminum oxide layer during the cutting of the
sample ingot. This possibility was investigated by cleaning the
surface of the C95500 coupons with a coarse grit paper and
repeating the tests for 6 h. This cleaning procedure resulted in
a 3-log-greater reduction in E. coli viability after 6 h (data not
shown) when meat juice was not present. However, with the
beef juice added, the cleaning procedure resulted in no signif-
icant difference in the reduction in E. coli viability. Findings
suggest a “protective layer” was present, but even after re-
moval the copper itself is “locked” into the alloy by some
unknown action of the beef residue. Further investigation into
these findings is required. Tests on pure aluminum showed
no detrimental effect (data not shown) on the viability of E.
coli O157.
To conclude, the inhibitory effects observed in these com-
monly used cast copper alloys are an intrinsic property of these
materials. Although stainless steel surfaces may appear to be
clean, this study has shown that bacteria can survive on these
surfaces for considerable periods of time. In comparison, sur-
vival on many copper alloys is limited to just a few hours or
even minutes. Due to the intrinsic characteristics of copper
alloys, i.e., homogeneous and solid, superior lifetime antimi-
crobial efficacy, wear resistance, and durability, they could be
utilized in facilities where bacterial contamination cannot be
tolerated. As such, copper-based work surfaces could provide
an important additional protective barrier to complement what
should always be existing good cleaning practices in food pro-
duction and retail facilities. Considering the low infectious
dose of a dangerous pathogen such as E. coli O157 and its
ability to survive for long periods in the environment, all pos-
sible protective barriers to prevent transmission through the
food chain should be utilized.
ACKNOWLEDGMENTS
This study was supported by the Copper Development Association,
New York, with assistance from the International Copper Association,
New York.
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Nursing Research January/February 2002 Vol 51, No 1 http://www.nursingcenter.com 1
A Meta-Analysis of Fall Prevention Programs
for the Elderly
How Effective Are They?
Elizabeth E. Hill-Westmoreland
�
Karen Soeken � Ann Marie Spellbring
� Background: Although fall prevention studies for the elderly
have been reported, there is a paucity of work summarizing
the effectiveness of these interventions.
� Objectives: The research question that guided this study was:
“What are the effects of fall prevention programs on the pro-
portion of falls in the elderly?”
� Method: Meta-analysis was employed to summarize findings of
intervention studies of fall prevention in the elderly involving
a comparison group and a quantifiable outcome. Studies
were reviewed by two of the authors with the eligibility crite-
ria in mind. Studies were then coded and an inter-rater reli-
ability check was performed.
� Results: The overall mean weighted effect size for the 12 stud-
ies included in the meta-analysis was .0779 (Z � 5.03, p �
.001). For fall prevention intervention types, exercise alone
had a mean weighted effect size of .0220 (Z � .5303, p �
.5), exercise and risk modification had a mean weighted
effect size of .0687 (Z � 3.41, p � .001), and comprehen-
sive risk assessment intervention studies had an effect size
of .1231 (Z � 3.97, p � .001). The mean weighted effect
size size for community-based studies was .0972 (Z � 5.37,
p � .001) and for institution-based studies was .0237 (Z �
.7822, p � .22). Time to outcome measure analyses
revealed that the mean weighted effect size for studies mea-
suring proportion of falls at 12 months was .0905 (Z � 5.43,
p � .001), and those measuring at four months or less was
�.0972 (Z � �.005, p � .50).
� Conclusions: The results of this meta-analysis indicate that
there was a 4% decrease in the rate of falls for individuals
who were in the treatment groups receiving various fall pre-
vention interventions. Additional intervention studies need to
be conducted in the elderly population with a goal of pre-
venting falls.
� Key Words: elderly • fall prevention • meta-analysis
alls are a common problem in the elderly population.
In community-dwelling individuals age 65 and older,
approximately one-third fall every year (King & Tinetti,
1995).Once elderly individuals are institutionalized, their
potential for falls multiplies. For elderly individuals resid-
ing in long-term caring settings, the incidence of falls
approaches 50% (Rubenstein, Josephson, & Robbins,
1994). Much attention has been devoted to the problem of
falls in the elderly, as evidenced by numerous studies
throughout the gerontology literature focusing on the risk
factors for falls. Studies of risk have examined both intrin-
sic factors (such as physiological changes and medica-
tions), as well as extrinsic factors (environmental factors
such as lighting, faulty equipment and floor surfaces) that
might contribute to falls in this population. During the
1990s an increase in studies of fall prevention interven-
tions began to appear in the gerontology journals.
Although a variety of intervention studies focusing on
fall prevention have been conducted during the 1990s,
with a trend toward targeted risk abatement and exercise,
very little has been done to synthesize the results of these
studies. Systematic reviews have been conducted to sum-
marize the literature related to fall risk factors (Rawsky,
1998) and fall prevention programs (Anonymous, 1996) in
the elderly. However, few attempts have been made to syn-
thesize the results of studies of the effectiveness of fall pre-
vention strategies using meta-analytic techniques. One
meta-analysis combined the results of seven studies that
were part of the Frailty and Injuries: Co-operative Studies
of Intervention Techniques (FICSIT) project (Province et
al, 1995). The FICSIT project combined various forms of
F
Elizabeth E. Hill-Westmoreland, MS, RN, CS, is a Doctoral Can-
didate, University of Maryland at Baltimore School of Nursing.
Karen Soeken, PhD, is Associate Professor, University of Mary-
land at Baltimore School of Nursing.
Ann Marie Spellbring, PhD, RN, is Associate Professor, Univer-
sity of Maryland at Baltimore School of Nursing.
2 Meta-Analysis of Fall Prevention Intervention Studies Nursing Research January/February 2002 Vol 51, No 1 http://www.nursingcenter.com
exercise with other interventions. The results of the meta-
analysis revealed that those in the exercise group had an
estimated 10% lower risk of falling than the controls
(Province et al, 1995).
The meta-analysis of the FICSIT project, however, did
not include the results of other studies of fall prevention
and was limited primarily to studies of exercise interven-
tions. To date, the impact of the various types of fall pre-
vention programs on the rate difference of falls in the
elderly population has not been reported and provides the
rationale for conducting a meta-analysis in this area.
Purpose, Research Question,
and Variable Definitions
The purpose of the study was to examine the effectiveness of
strategies for preventing future falls by synthesizing the indi-
vidual studies of fall prevention. The research question that
guided the study was: “What are the effects of fall preven-
tion programs on the proportion of falls in the elderly?”
Falls were conceptually defined as coming to rest on the
ground, floor, or other lower level, unintentionally (Buchner
et al., 1993). In this meta-analysis the specific outcome of
interest is the rate of difference or the difference in the pro-
portion of falls in the experimental group versus the control
group (Shadish & Haddock, 1994). The independent vari-
able in this study included any type of intervention strategy
that was performed with the goal of fall prevention.
Methods
Literature Search: A variety of search techniques were
employed to identify published studies of fall prevention pro-
grams in the elderly. Searches were performed using Medline
(1966-1999) and Cumulative Index for Nursing and Allied
Health Literature (CINAHL) (1982-1999) computerized
databases. The database searches were limited to articles
published in the English language using combinations of the
keywords “aged or elderly,” “falls,” “fall prevention,” “acci-
dental falls,” “interventions,” “intervention studies,”
“experimental studies,” and “results.” The database searches
of Medline and CINAHL revealed a total of 139 articles.
Each of these 139 abstracts was reviewed with the research
question in mind. Eleven of the 139 abstracts that appeared
to include the variables of interest were used for citation
searching (Reed & Baxter, 1994) of the Social Sciences Cita-
tion Index (SSCI) and the Science Citation Index (SCI) com-
puterized databases. The citation search of the SSCI and SCI
revealed three additional abstracts that appeared to include
the variables of interest for this meta-analysis.
Additional search strategies were used to supplement
the computerized databases, which can miss as many as
50% of studies when used in isolation (Cooper & Hedges,
1994). The ancestry approach or footnote chasing (White,
1994), utilized to uncover additional studies from refer-
ence lists, yielded three articles that were reviewed for
inclusion in the meta-analysis. The third author located
another two studies.
Study Selection: Nineteen studies identified through the
search were obtained and were independently reviewed (by
the first and third authors) for inclusion in the meta-analy-
sis. Studies were included if they met the following eligibil-
ity criteria: (a) sample included only older adults 60 years
of age or older; (b) inclusion of some type of fall preven-
tion intervention; (c) use of a comparison group on out-
come measure; (d) sufficient information to determine the
rate of difference in falls as the outcome measure; and, (e)
the number of participants in the study groups was speci-
fied in the article. The reviewers agreed that 11 studies met
these eligibility criteria. Reviewers disagreed on a 12th
study that was then reviewed by the second author who
deemed the study met the eligibility criteria. These 12 stud-
ies were included in this meta-analysis.
Seven studies failing to meet the inclusion criteria were
eliminated from this meta-analysis. One study by Mitchell
& Jones (1996) was eliminated because some of the study
participants were less than 60 years of age, some were as
young as 38. Six of the studies failed to provide enough
information for the proportion of fall rate difference to be
calculated (Fiatarone et al, 1994; Kilpack, Boehm, Smith,
& Mudge, 1991; Province et al, 1995; Shumway-Cook,
Gruber, Baldwin, & Liao, 1997; Wolf et al, 1996; Mosley,
Galindo-Ciocon, Peak, & West, 1998).
Data Collection Methods: After initially reviewing the 12
studies to be included in the meta-analysis, variables were
selected for inclusion in the codebook. Coded were:
author, year, retrieval source, setting, country, time to out-
come measure, study design, type of fall prevention inter-
vention, number of subjects in the study groups, mean age
of the study sample, proportion of falls for the treatment
and control groups, and study quality.
A modified version of the “Research Quality Scoring
Method” by Sackett and Haynes (1976) was used to code
study quality (Table 1). Using this quality rating scale, the
range of total quality points was 0 to 6. For coding pur-
1. Study Design (0 – 3)
0 = one group pre-test/post-test
1 = nonrandomized retrospective data
2 = nonrandomized prospective experiment
3 = randomized experiment
2. Clarity of Outcome Construct Definition (0 – 1)
0 = no definition of “falls”
1 = “falls” clearly defined
3. Outcome Measure (0 – 1)
0 = subjective measure of “falls” (i.e., self-report, report via
survey, or retrospective review of records)
1 = objective measure of “falls” (i.e., documented by staff
during course of study as fall events occurred)
4. Indication of Time Until Falls Outcome Measure (0 – 1)
0 = not specified
1 = clearly indicated
TABLE 1. Study Quality Ratings for the Meta-
Analysis
Nursing Research January/February 2002 Vol 51, No 1 http://www.nursingcenter.com Meta-Analysis of Fall Prevention Intervention Studies 3
poses the studies with scores 0-3 were considered low qual-
ity and those with scores 4-6 were considered high quality.
All studies were rated for quality by the first author. To
determine the reliability of the ratings, two other raters
applied the quality rating scale to four randomly selected
studies and the Intraclass Correlation Coefficient (ICC)
was calculated as a measure of the consistency among the
three raters. The single measure ICC was .905 (95% CI:
.80 � .96) with the average measure ICC of .97 (95% CI:
.92 � .99). When the primary rater was paired with each
of the other two raters, the ICC values were 1.0 and .86.
After variables were selected, data coding forms were
developed to extract data from the articles. Because only
one coder extracted the data from all 12 articles, another
coder extracted data for three randomly selected articles
(25%) for inter-rater reliability. Coder agreement was ini-
tially 91%. Coders then reviewed those items for which
there was lack of agreement and consensus was reached.
The data were then entered into an SPSS version 10.0
(SPSS, Inc., Chicago) data file.
Statistical Methods: An effect size (d’) was calculated for
each of the individual studies using the difference between
population proportions formula (Becker, 1994). Specifi-
cally, in this meta-analysis the effect size for each study was
calculated by subtracting the proportion of falls for the
experimental group from the proportion of falls for the
control group so that a positive effect size favors the exper-
imental group. An overall mean weighted effect size for the
12 studies was calculated weighting for study variance. As
a means of sensitivity analysis, another mean weighted
effect size was computed only for those studies considered
high quality, again using differences in proportions and
weighting by variance. In an effort to determine whether
results of the synthesis were sensitive to the inclusion or
exclusion of low quality studies, the three studies not
receiving a high quality rating were not included in this cal-
culation: Schoenfelder & Van Why, 1997; Tinetti et al.,
1994; Uden, Ehnfors, & Sjostrom, 1999. In addition, 95%
confidence intervals were calculated for each effect size
and for the overall mean effect size.
Results
General Description: The 12 study samples that meet eligi-
bility criteria (Table 2) included a large proportion of
women (overall 79.5%). The samples in this meta-analysis
had a mean age of 76.5 years. Overall, the studies were of
high quality, with nine of the 12 studies scoring at least a
4 of 6 on the quality rating measure previously described.
The primary studies included a broad range of inter-
ventions (Table 3). Eight of the studies included some form
of an exercise intervention in addition to some other fall
prevention strategies. These eight studies were divided into
two subgroups. One group included three studies that had
exercise-focused interventions only (Campbell et al., 1997;
Lord, Ward, Williams, & Strudwick, 1995; Mulrow et al.,
1994). The second group included five studies with exer-
cise interventions, as well as other forms of risk modifica-
tion (Reinsch, MacRae, Lachenbruch, & Tobis, 1992;
Schoenfelder & Van Why, 1997; Tinetti et al., 1994; Uden
et al., 1999, Wagner et al., 1994). Three of the studies per-
Proportion of
Subjects Who Fell
Number of
First Author Year Subjects Mean Age Design Control Experimental
Campbell 1997 233 84.1 R 0.530 0.457
Close 1999 397 78.2 R 0.521 0.321
Lord 1995 169 71.7 R 0.479 0.454
Mulrow 1994 180 80.6 R 0.432 0.478
Ray 1997 417 82.7 Q 0.566 0.482
Reinsch 1992 230 74.4 Q 0.380 0.400
Rubenstein 1990 160 87.1 R 0.753 0.709
Ryan 1996 45 78 R 0.200 0.100
Schoenfelder 1997 14 74.6 Q 0.462 0.143
Tinetti 1994 291 77.9 Q 0.472 0.354
Uden 1999 379 74.4 Q 0.170 0.205
Wagner 1994 1559 72.5 R 0.368 0.283
Note. Design: R = Randomized Experiment (subjects randomly assigned); Q = Quasi-Experiment.
TABLE 2. Studies Included in Meta-Analysis of Fall Prevention in the
Elderly
4 Meta-Analysis of Fall Prevention Intervention Studies Nursing Research January/February 2002 Vol 51, No 1 http://www.nursingcenter.com
formed interdisciplinary comprehensive risk assessments
with recommendations made for specific interventions
based upon these assessments (Close et al., 1999; Ray et
al., 1997; Rubenstein, Robbins, Josephson, Schulman, &
Osterweil, 1990). A final study used community education
related to fall prevention with environmental modifica-
tions made by subjects (Ryan & Spellbring, 1996).
Pooled Results: Effect sizes and 95% confidence intervals
were calculated for each individual study and for the over-
all mean weighted effect size (MWES) for the 12 studies
(Figure 1). The overall MWES for the 12 studies is .0779
(Z � 5.03, p � .001) based on N � 4074 with a 95% CI
.0475 to .1083. Thus across the 12 studies the results indi-
cate the intervention is effective in reducing the proportion
of falls incurred.
Subgroup Analyses: The variability of effect sizes for the
complete set of studies (N � 12) and within subsets of
studies was examined using the Q-statistic. When the test
for heterogeneity of variance in effect sizes of the 12 stud-
ies (QT � 17.70, df � 11) was found to be significant at p
� .10, partitioning of the variance was performed. Het-
erogeneity was then partitioned according to the four types
of intervention groupings and homogeneity of variance of
effect sizes was found within all of the intervention groups.
Using alpha � .05, the Q-statistic suggest the 12 studies
have similar findings.
To determine the effectiveness of the three major types
of interventions combined in this meta-analysis, a MWES
was calculated for each of the following groups of studies:
(a) three studies using strictly exercise interventions (EX);
(b) five studies using exercise and risk factor modification
Interventions 1 2 3 4 5 6 7 8 9 10 11 12
Exercise of some type
Walking or low-intensity X X X X X X X
Resistance or muscle strengthening X X X X X X
Range of motion X X X X
Reaction time X X
Mobility
Gait training X X X X X
Balance or coordination X X X X X X X X
Transfers X X X X
Proper use of walking aids X X
Educational information
Fall risk and prevention X X X X
Relaxation training X X
Staff training on prevention X X
Screening and referrals
Vision X X X X
Hearing X X
Alcohol abuse X
Mental status X X X X X
Depression X X X
Biological and physical assessments
Blood pressure measurement X X X X X
Various lab tests X
Carotid sinus studies X
EKG X
24-hour holter monitor X
Modifications
Medication recommendations X X X X X X
Personal or environmental safety X X X X X X X X X
Note. Numbers in the heading indicate the first author of each study: 1 = Campbell, 2 = Close, 3 = Lord, 4 = Mulrow, 5 = Ray, 6 = Reinsch, 7 = Rubenstein, 8 =
Ryan, 9 = Schoenfelder, 10 = Tinetti, 11 = Uden, 12 = Wagner.
TABLE 3. Description of Study Interventions
Nursing Research January/February 2002 Vol 51, No 1 http://www.nursingcenter.com Meta-Analysis of Fall Prevention Intervention Studies 5
(EXRM); and (c) three studies using an interdisciplinary
comprehensive risk assessment (CRA) approach (Figure 2).
Because the interventions used in Ryan & Spellbring
(1996) were considerably different from the intervention
approaches of the other study groupings they were omitted
from this subgroup analysis. The mean weighted effect size
for the EX intervention studies was .0220 (Z � .5303, p �
.5) with 95% CI of �.0593 to .1033. The mean weighted
effect size for the EXRM studies was .0687 (Z � 3.41, p
� .001) with a 95% CI of .0292 to .1082. The mean
weighted effect size for the CRA studies was .1231 (Z �
3.97, p � .001) with a 95% CI of .0623 to .1839.
The studies were grouped according to two major types
of settings, community-based and institutional, to examine
whether differences in effect sizes occurred. For the com-
munity-based studies the MWES was .0972 (Z � 5.37, p
� .001) with a 95% CI of .0617 to .1327 (Figure 2). The
MWES for the institution-based studies was .0237 (Z �
.7822, p � .22) with a 95% CI of �.0357 to .0831. The
analysis suggests that community-based interventions
demonstrate a significant effect on proportion of falls
where institution-based interventions did not.
Because studies differed in the time point at which the
outcome (proportion of falls) was measured, the studies
were grouped based on time. One group was comprised of
eight studies that measured proportion of falls 12-months
into the study period; the other consisted of the four stud-
ies measuring the outcome at four months or less. The
MWES for the 12-month group was .0905 (Z � 5.43, p �
.001) with a 95% CI of .0578 to .1232 and the MWES for
the 4-month or less group was �.0972 (Z � �.005, p �
.50) with a 95% CI of �.0810 to .0806 (Figure 2). Thus,
studies that measured proportion of falls at 12-months
demonstrated significant effects, but those that measured
them at four months or less did not.
Sensitivity Analyses: A sensitivity analysis was performed
based upon the study quality rating (range of scores 0 to
6). Nine of the 12 studies scoring between 4 and 6 on the
quality rating scale were assigned a high quality rating
while the remaining three studies were assigned a low
quality rating (Table 4). The MWES for the high quality
studies was .0812 (Z � 4.86, p � .001) with 95% CI of
.0485 to .1139 while the MWES for the low quality stud-
ies was .0593 (Z � 1.55, p � .07) with a 95% CI of
�.0193 to .1379 (Figure 2). Results indicate that inter-
ventions in high quality studies demonstrated a significant
reduction in proportion of falls whereas low quality stud-
ies did not.
Publication Bias: A fail-safe N � 56 was computed for the
standardized Z of the 12 studies, using the “meta” com-
FIGURE 1. Fall prevention
programs and rate difference
of falls: Meta-analysis results.
Effect sizes and 95% confi-
dence intervals.
6 Meta-Analysis of Fall Prevention Intervention Studies Nursing Research January/February 2002 Vol 51, No 1 http://www.nursingcenter.com
puter program (http://nw3.nai.net/~dakenny/meta.htm) by
David Kenny (1999), indicating the number of studies hav-
ing an average effect of zero needed to reduce the overall
effect to nonsignificance (Becker, 1994). Another means of
identifying publication bias is by examining a funnel plot
of sample size versus effect size (Figure 3). In the funnel
graph the spout is pointing up and the funnel is not
skewed. The characteristics of this plot indicate that the
problem of publication bias is unlikely in this meta-analy-
sis (Begg, 1994).
Discussion
In this study, the effects of fall prevention interventions on
the proportion of falls were found to be small (Cohen,
1992). Experimental mortality within each of the studies
FIGURE 2. Fall prevention programs and rate difference of falls for various subgroups. Mean effect sizes and 95% confidence intervals. EXRM � Exer-
cise and Risk Modification, CRA � Comprehensive Risk Assessment.
FIGURE 3. Funnel graph of 12 fall prevention
studies.
�
Nursing Research January/February 2002 Vol 51, No 1 http://www.nursingcenter.com Meta-Analysis of Fall Prevention Intervention Studies 7
may have contributed to this overall small effect. Five of the
12 studies (Schoenfelder & Van Why, 1997; Tinetti et al.,
1994; Mulrow et al., 1994; Ray et al., 1997; and Lord et al.,
1995) reported that the proportion of falls was calculated
after individuals who dropped out of the study were
removed from the number of individuals in each of the
study groups. Thus, the majority of the studies either
included individuals who had dropped out in computing
their outcome measures or failed to report study dropouts.
These factors may contribute to an overall small effect size.
Original study authors may have included dropouts in the
numerators upon which proportion of falls calculations
were based; it was not possible to remove dropouts from the
denominator when calculating proportion of falls because
the number of dropouts was not known.
When analyses were performed to examine the EX,
EXRM and CRA programs, the results of the EX grouping
were not statistically significant. However, the MWES for
the EXRM programs and the CRA programs were statisti-
cally significant. The importance of using an approach to
fall prevention that does not focus solely on exercise is
supported by the larger effect sizes for the EXRM and
CRA programs and their statistical significance.
When analyses were performed examining effect sizes
according to study setting, the MWES was larger for the
community-based studies than for the institution-based
studies. These findings indicate that when compared, the
community-based fall prevention programs were more
effective. Generally, individuals residing in the community
tend to be less frail than those residing in institutional set-
tings (Rubenstein, Josephson, & Osterweil, 1996) which
helps to explain this finding.
The analyses performed based upon time-to-outcome-
measure demonstrated a small but statistically significant
MWES for studies measuring proportion of falls at 12-
months. However, the MWES was negative and not statis-
tically significant for studies measuring proportion of falls
at four months or less. The results suggest that fall preven-
tion interventions show the greatest effects when the out-
come is measured for the long-term effect, in this case, 12-
months after the interventions had been initiated. Finally
analyses were performed according to type of study design.
The MWES for randomized experiments was larger than
those for the quasi-experiments. Only the randomized
grouping was statistically significant. These findings sug-
gest that the more tightly controlled studies were more
effective at preventing falls. The practical importance of
the overall effect size of .0779 is best presented in terms of
a Binomial Effect Size Display (Rosenthal, 1994). The
interpretation of this finding is that there was a 4% (from
52% to 48%) decrease in the rate of falls for individuals
who were in the treatment groups receiving various fall
prevention interventions.
Most of the research in the area of falls in the elderly in
the 1980s had the goal of identifying the risk factors
related to falls. During the 1990s and in the current decade
studies of the effectiveness of fall prevention programs
have become more common. Based upon the overall
MWES found in this meta-analysis, additional studies are
needed to enhance the effectiveness of fall prevention pro-
grams. Consistently including the rate difference of falls as
an outcome measure will permit additional meta-analyses
to be conducted and promote the development of knowl-
edge in this important area. �
First Author Study Quality Study Setting* Intervention Type† Time to Outcome Effect Size Variance
Campbell High C EX 12 months 0.073 0.004
Close High C CRA 12 months 0.201 0.002
Lord High C EX 12 months 0.025 0.006
Mulrow High LTC EX 4 months �0.047 0.006
Ray High LTC CRA 12 months 0.084 0.002
Reinsch High C EXRM 12 months �0.020 0.006
Rubenstein High R CRA 12 months 0.044 0.005
Ryan High C ED 3 months 0.100 0.014
Schoenfelder Low C EXRM 3 months 0.319 0.029
Tinetti Low C EXRM 12 months 0.119 0.003
Uden Low H EXRM Not specified �0.035 0.004
Wagner High C EXRM 12 months 0.086 0.001
*Study setting: C = community; LTC = long term care; R = residential care with varying levels; H = hospital
†Intervention Type: EX = exercise; EXRM = exercise and risk modification; ED = education & environmental modification; CRA = comprehensive risk assessment
TABLE 4. Study Effect Size
8 Meta-Analysis of Fall Prevention Intervention Studies Nursing Research January/February 2002 Vol 51, No 1 http://www.nursingcenter.com
Accepted for publication July 11, 2001.
The authors thank John Westmoreland, Information Systems Business
Analyst, First Union National Bank, for his assistance with the graph-
ical presentation of the data presented in this article.
Corresponding author: Elizabeth E. Hill-Westmoreland, MS,
RN, CS, University of Maryland at Baltimore, School of Nursing,
Room 462, 655 West Lombard Street, Baltimore, MD 21201 (e-mail:
Bleedbandw@aol.com).
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