Designing an Experiment First consider a WS design with counterbalancing. For this design you must be logically able to run the conditions in any order. Control for sequencing effects by ensuring that all conditions are effected equally by order and carry-over effects. Not appropriate for: - treatment outcome studies (pre-post type) - manipulations that have permanent carry-over effects. ch9(2)
Consider a Pre-Post Test design with a randomly assigned, no-treatment control group. Not as powerful because half of your participants are needed for the control group. Controls for Confounds due to time (History, Maturation, Instrumentation, Testing, Attrition and Statistical Regression) by obtaining a measure of the confounds that can be accounted for in the analysis. ch9(2)
Least powerful design because of individual difference confounds. Only when a Within Subjects design cannot be conducted would a Between Subjects design be used. Least powerful design because of individual difference confounds. Eliminate individual differences confounds using a process that should produce groups that are comparable. If N per condition < 15, us a matching technique. ch9(2)
Pre-post Double Blind Placebo Control Group Design Chapter 8 Pre-post Double Blind Placebo Control Group Design Pre Post Treatment (experimental) Placebo Control ch9(2)
Faulty Research Designs One Group After-Only Designs one measure of the DV, obtained after treatment is given. Problems: Pre Post Treatment (experimental) Placebo Control ch9(2)
One Group Before After (Pre-post) Design Like the pre-post placebo control design, without the placebo control. Problems: Pre Post Treatment (experimental) Placebo Control ch9(2)
Non-Equivalent Control Group a control group that has not been obtained by random assignment. e.g., matching, logical comparisons, frequency distribution control. Randomization – is the only means by which unknown confounding extraneous variables can be controlled. ch9(2)
Requirements of True Experimental Research Design. - Comparison being made between 2 or more conditions of an IV. The difference between these conditions is produced by the researcher. All other confounds are controlled by ensuring that they are 1) eliminated, 2) effect all conditions equally or 3) are measured so their effects can be accounted for in the comparison. All measures are unbiased. ch9(2)
Why use a pretest within subjects control condition Increased sensitivity – can use matching techniques to reduce variance (i.e., lowers sx) Control for Ceiling Effects - can the treatment have an effect? Gives Measure of Initial Position. Can see if initial position determines treatment outcome. ch9(2)
Can determine initial comparability of between group comparisons (useful for nonequivalent control group designs) Pre Post Treatment (experimental) Placebo Control ch9(2)
If your research question is that the IV causes a change – a pre-test control is the logical control group. ch9(2)
Between Participants - After Only Design Compares Treatment Group to Control Group Different subjects in each condition Individual difference confounds. Pre Post Treatment (experimental) Placebo Control ch9(2)
Control Individual Difference Confound by: __________ If Random Assignment is not used then this is a non-equivalent Posttest-only design. Pgs 246 to 255 (Factorial Designs) will NOT be on Exam 3. ch9(2)