Moderation, mediation and more regression

Moderation, mediation and more regression

1. What is moderation?

   • When the relationship between two variables changes as a function of the third variable
     • The model: a regression in which the outcome is predicted from the predictor, the moderator and their interaction
       • Centre the predictors
       • If the interaction is significant there is a moderation
         • Simple slopes: look at the relationship between the predictor and outcome at low, mean and high levels of the moderator

2. How do i include categorical predictors into my model?

   • Dummy coding: categorical variables with more than two categories are coded into variables all of which have values of only 0 or 1

3. What is mediation?

   • The strength of the relationship between a predictor variable and outcome variable is reduced by including another variable as a predictor
     • Direct effect: the effect of the predictor independent of the mediator
     • Indirect effect: the effect of the predictor through the mediator
       • Effect size: kappa-squared
       • Bootstrap 95% CIs