1. Experimental Design

2. Placebos

3. Go through paper expectations

4. Validity What is internal validity? How can it be increased?
What are the relationships between internal, external, and construct validity?
What is needed to establish causality?

5. Campbell & Stanley, 1963 Threats to Internal Validity
History
Maturation
Testing
Instrumentation
Mortality
Regression to the mean
Selection
Diffusion of treatments

6. Regression to the mean Why does it happen? When will it happen more?
How can you estimate it?

7. Design notation
X O
R O X O
R O O
N O X O
N O O
N O

8. Importance of random assignment
vs. random selection
What is the strongest design in terms of internal validity threats?
Why would you want to add a pretest? Or not?
Are there times that you wouldn’t want to randomly assign?

9. Basic design terms Independent vs. dependent variables
Within vs. between-participants designs: advantages?
What are control variables?
What can you do to reduce confounds in research?

10. Factorial designs What are they, and why do we care?
What are levels vs. variables?
What kind of FD is this? How many main effects are possible? How many interactions? How many groups? How many people at n=10?
IVs: Presence of an audience, difficulty of task (easy, medium, or hard). DV = nervousness
IVs: Gender, Drug vs. CBT vs. control, previous experience with treatment (yes or no), and time (immediate vs. 3 months later). DV=symptoms

11. Main effects and interactions
People who were alone helped more often than those who were with a confederate. Seminary students also helped more often than business students.
Men and women helped equally overall, but men were more likely to help women than to help men.

12. Examples on sheets

13. Terms Null results Main effect Interaction Block design Covariate
Solomon 4-group
Switching design
ANOVA vs. ANCOVA vs. regression

14. Issues related to design
If a factorial design is good, is a bigger one better?
When would you want to include a variable as an IV vs. a covariate vs. something you match on vs. a control variable?
What are the best covariates?
How do you decide which variables to include?

15. Bless & Burger, 2016 Table 1 Alternative explanations for IVs:
Is is the level or the fact that it changed that caused the effect?
Does the effect change over time?
Is it just an increase in accessibility?
Is there an effect of a manipulation check?
Would a stronger manipulation increase or decrease the effect?
Do initial levels of participants affect results?
Is the effect due to manipulation being surprising?

16. How can you deal with these?

17. Random assignment—What negative effects could there be of that?
How can you address this issue?

18. Experimental control of the situation—what problems does that introduce?
How can you address those?
How would all of these affect external validity?

19. Lab experiments and external validity
Mitchell, 2012
How do we usually deal with complaints about ext val with experiments?
Do lab and field studies get the same results?
Why would some areas generalize better than others?
Table 2
Table 3

20. Moderators What is a moderator? How is a moderator different from a/an
IV?
DV?
Confound?
Mediator?
Covariate?
Interaction

21. Mediators What is a mediator? How is a mediator different from a/an
IV?
DV?
Confound?
Moderator?
Covariate?

22. Examples
A study finds that convicted criminals are more likely than noncriminals to score low (negatively) on the Attitudes toward Women Scale. Further research shows, however, that this is only true for violent criminals. There is no relationship between nonviolent criminal activity and negative attitudes toward women. Identify the mediator or moderator. 
2. A researcher finds that by increasing self-focus in children, she can decrease their likelihood of cheating on a test. By decreasing cheating, in turn, she finds that academic self-efficacy increases. Identify the mediator or moderator.
3. Dr. Laylor finds a relationship between physical attractiveness and self-confidence. He later determines that the primary cause of this relationship is the positive feedback physically attractive people receive from others. Identify the mediator or moderator.
4. Boys who are popular with the same-sex tend to also be popular with the opposite-sex, whereas girls who are popular with the same-sex tend to be less popular with the opposite-sex. Identify the mediator or moderator.
5. Identify and explain at least two potential mediators and two potential moderators for the following relationship: School size and academic achievement.

23. Testing moderation Dummy vs. effect coding Simple slopes
Mean centering vs. standardized variables
Ways to test:
Slope for interaction <>0
Whether model has smaller ss error than model without interaction
Test partial correlation with interaction and Y, controlling for X and Z

24. Mediation issues What are the criteria to show mediation?
What is a suppressor variable?
What are the assumptions of a mediational relationship?
How do you know which variable is the mediator if you do a cross-sectional study?
Experimental causal chain design
Testing process by interaction strategy

25. Testing mediation Causal steps (a & b joint significance test)
Differences in coefficients
Product of coefficients (Sobel test)
PRODCLIN

26. More issues Single vs. latent measures
Multi-level mediation/moderation
Dependency
Mediated moderation
Moderated mediation
Restriction of range

27. Outlines Think of sections as headings in your thesis
Keep headings parallel
Always have at least 2 in each group
Think about the best logical order for things, and keep the order consistent throughout the paper
Be detailed
Due next week!

28. Next week Quasi-experiments
2 book chapters plus chapter on field and one on clinical