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November 22

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Anna Nagy

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Nov 22, 2010 Ch.8
Pretest-Posttest Design
= A pretest is given before the experimental manipulation is introduced to make sure groups are
equivalent at the beginning of the experiment
Advantages of the pretest-posttest design
-Mortality (dropout factor)
-Assess equivalency of groups with small sample size
-Can use to select participants for the experiment
Disadvantages of the pretest-posttest design
-Time consuming and awkward to administer
-Sensitize participants to what is being studied
-Demand characteristics
-Reduces external validity
No Pretest effect:
Results for posttest only and pretest-posttest conditions have no significant differences in both control and
experimental groups
Repeated Measures Design
-Fewer participants
-Extremely sensitive to statistical differences
-Conditions are identical because person is own control group
-‘Carry over effects
-Practice effect
- Fatigue effect
-Contrast effect
-Habituation (reduced responsiveness)
-Sensitization (stronger response)
-Adaptation (e.g. develops tolerance)
Issues to consider in repeated measures designs
1. Counterbalancing(Changing orders for experiment for studies to control for order effect)
-Complete counterbalancing
-Latin squares
Constructing Latin squares
Determines orders of N number of conditions
4 conditions=4 orders
8 conditions=8 orders
Each condition or groups appears once at each order and each condition precedes and
follows each other condition one time
*Remember formula for first row!! Then continue using row.
Need 2 Latin squares for odd number
1. Determine the number of conditions, and use letters of the alphabet to represent
them: ABCDEF for six conditions
2. Determine the order for the first row, using the following ordering:
AB L C L-1 D L-2 E etc…(L=final condition)
What would order for six conditions be?

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