1. Psychology 202b Advanced Psychological Statistics, II March 1, 2011

2. Overview Recapping stepwise regression. Regression with categorical predictors –Simple (two groups) –More complex (several groups) Interactions between categorical and continuous predictors.

3. Reasons not to use stepwise procedures Atheoretic –Can result in nonsensical models. –Cannot test particular models that make sense. Where is the assumption checking? Danger of capitalizing on chance. Difficult to cross-validate.

4. Regression with categorical predictors Simplest possible example: two groups –Dummy coding smoking A more complex example –Dummy coding father’s occupation Illustration with the BMI data

5. A quick digression on ANOVA Dunnett’s test in SAS.

6. Mixing categorical and continuous variables Centering A simple example: BMI, smoking and family income A more complex example: BMI, father’s occupation and family income

7. Next time A little more on interactions. Power analysis for regression.