discussion
Present the five major parts of APA papers and the information contained in each part.
Discuss Barber’s (1976) 13 ways to improve Psychological Research (page 254, Box 11.1)
What does it mean to say that experimenter bias affects internal validity?
Provide three examples of experimenter bias
Be sure you can identify IV’s and DV’s
Be able to design experiments using the designs discussed in Chapter 8
Control: The Keystone of the Experimental Method
Research Methods in Psychology
You will Learn:
Control Achieved Through Participant Assignment and Selection
Randomization
Control Achieved Through Experimental Design
Control as Related to the Logic of Experimentation
Control achieved through participant assignment and selection
Random Selection from a large subject pool produces a representative sample
Asking for volunteers from a large subject pool who are informed of the nature of the study before volunteering does not produce a representative sample
Control achieved through participant assignment and selection
Random Number Tables may be useful in selecting subjects from a larger pool of potential subjects.
Volunteers gather in one room and you assign them a number.
Using the random number table you then select those who’s numbers show up in the table.
100 volunteers, use 2 digits (11, 74, 26, 93, 81, 44, etc.) until you have the number of subjects you want.
Control achieved through participant assignment and selection
With the total number of subjects randomly selected from the larger pool of volunteers you can now randomly assign subjects to the different groups using the random numbers table again.
Three Groups? Use 1,2,3 only.
First subject = group 1
Second subject = group 1
Third subject = group 2
Fourth subject = group 3
Control achieved through participant assignment and selection
Elimination Procedure
Equating Procedure
Use Random Number Table to assign subjects to groups, but assign equal numbers of subjects with same characteristics to each group.
Eliminate Subjects In Order to Achieve Control
Results Then Apply Only to Those With Same Characteristics as Sample
Control achieved through participant assignment and selection
Counterbalancing Procedure is another good way to assign subjects to groups
Incorrect: First person = group 1, Second person = group 2, Third person = group 1, etc.
Incorrect: First male = group 1, First female = group 1, Second male = group 2, Second female = group 2, Third male = group 1, Third female = group 1, etc.
Correct: First male = group 1, First female = group 1, Second male = group 2, Second female = group 2, Third male = group 2, Third female = group 2, Fourth male = group 1, Fourth female = group 1, Fifth male = group 1, Fifth female = group 1, Sixth male = group 2, Sixth female = group 2, etc. (two by two)
Randomization
Random Sampling
Random Assignment
All potential participants have the same and equal chance of being chosen for participation.
University Participant Pools are composed of General Psychology Students (mostly freshmen, mostly young).
University Participant Pools are not the best sources for participants.
Assigning randomly sampled subjects to groups is also a random process.
Equating and Counterbalancing are not Random Assignments.
Random Assignment is only way to ensure all groups are equal on all characteristics (known and unknown).
Differences are not eliminated, but affect both groups equally.
Control Achieved Through Experimental Design
Experimental Design
Like a blueprint experimental design tells us how to “build” our study
Two Functions
1. able to determine the effect of an independent variable on a dependent variable
2. able to rule out confounds as alternative explanations
Control Achieved Through Experimental Design
Two types of variables
Independent variable (IV) – the factor or condition that is manipulated by the experimenter
Dependent variable (DV) – the variable that is measured, thought to be changed be the IV
Have at least two groups.
Experimental group – A group that is exposed to all experimental conditions including the independent variable or variable of interest
Control group – A group that is subjected to conditions almost identical to the experimental group but for whom the independent variable is not manipulated.
Participants must be assigned to groups randomly so that all participants have an equal chance of being assigned to any of the conditions.
Seek to avoid extraneous variables
Extraneous variables – any variables other than the independent variable that are likely to influence the dependent variable
Types of Experimental Design
Posttest-Only Control Group Design
Pretest-Posttest Control Group Design
Randomly assign people to groups
Group A: Give them treatment, then Measure
Group B: Gets no Treatment, then Measure
Does not rule out some of the Threats to Internal Validity
Randomly assign people to groups
Group A: Measure, then Treatment, then Measure again
Group B: Measure, then No Treatment, then Measure again
Controls Threats to Internal Validity
But does pretest introduce a confound?
Types of Experimental Design
The Solomon Four-Group Design
Randomly assign people to groups
Group 1: Pretest, then Treatment, then Posttest
Group 2: Pretest, then No Treatment, then Posttest
Group 3: No Pretest, then Treatment, then Posttest
Group 4: No Pretest, then No Treatment, then Posttest
Now the effect of a Pretest, if any, can be evaluated.
Solomon Four Group Design
Experimental Design
Four Characteristics of True Experiments
1. Random Assignment to Groups
2. Must have at least Two Levels of the Independent Variable (IV): Control Group and Experimental Group
3. Controls for Threats to Internal Validity
4. Compares two alternative Theories (but not always maybe)
Control as Related to the Logic of Experimentation
Random Selection and Random Assignment ensures groups are equal before the experiment begins.
A pretest may be given to double-check.
Is Experimental Design adequate to Test the Hypothesis?
Treat All Groups Exactly the Same, except for the Levels of the IV.
Interpretation of Results
You Have Now Learned:
Control Achieved Through Participant Assignment and Selection
Randomization
Control Achieved Through Experimental Design
Control as Related to the Logic of Experimentation