Chapter 10 Mediation Class 6 Spring 2015 Ang &Huan (2006)

Moderator vs. Mediator Moderator variable (“separator”)  When or for whom a variable X most strongly predicts an outcome (criterion) variable Y (strength and direction + or -) Mediator  The mechanism by which a predictor causes or explains the outcome

Moderation Analyses: Regression Predictor Moderator Outcome Predictor X Moderator High M Low M

Moderation Analyses: Regression P: Alcohol use M: Gender Depression Predictor X Moderator M F

Moderation Analyses: Regression P: Alcohol use M: Stress Depression Predictor X Moderator High Stress Low Stress

Mediation Establishes How or Why a variable causes or predicts the criterion (or outcome) variable. Mediator is the mechanism by which predictor causes or explains the outcome Predictor  Outcome Predictor  Mediator ---  Outcome Parent Drinking----  F. Conflict -  Low Self Esteem

7 Mediation The Beginning Model

8 The Mediational Model

9 Low Self- Esteem Parent Drinking Family Conflict

Baron and Kenny procedure 1. X  Y (test path c) 2.  M (test path a) 3. M (and X)  Y (test path b) 4. X (and M)  Y (test path c′ ) Analyses 3 and 4 use the same regression equation.

Hierarchical regressions analyses to test mediation Reg. 1 Predictor Outcome Prnt. Drinking c ----  Low Self Esteem Reg 2 Predictor Mediator Prnt. Drinking a  Family Conflict Reg 3 Mediator Outcome Family Conflict b  Low Self-Esteem (controlling for Predictor – Parent Drinking) Reg 3 Predictor ----  Mediator  Outcome Prnt. Drinking --  Fam. Conflict  Low Self Esteem C’

Regressions Mediation Analyses : Criterion (DV): Low Self Esteem Reg 1 (Path c) Reg 1 B β R 2 Step 1.25** Parent Drinking ** Reg 2 (Path a) Criterion (DV): Mediator -- Family Conflict Step 1.14** Parent Drinking **

Hierarchical Regression Mediation Analyses : Criterion (DV): Low Self Esteem (Paths b and C’) Reg 3 B β ΔR 2 R 2 Step 1.25 ** Parent Drinking (c) ** Step 2.05*.30** Parent Drinking (c’) Family Conflict (b) ** Controlling for predictor (PD), mediator (FC) is related to Outcome The relation of predictor to outcome disappears when moderator is added to the equation = Total mediation

Hierarchical Regression Mediation Analyses : Criterion: Low Self Esteem (Partial Moderation Reg 3A) B β R 2 Step 1 (Reg1).25** Parent Drinking ** Step 2B (Reg 3A) Parent Drinking Family Conflict *.09**..30** Controlling for predictor (PD), Mediator (FC) is related to Outcome The relation of predictor to outcome decreases when moderator is added to the equation. Is the decrease from.18 to.10 statistically significant?

Sobel Test Calculator Whether the indirect effect of the predictor on the criterion via the mediator is significantly different from zero Numbers needed  a = raw (unstandardized) regression coefficient for the association between predictor and mediator.  sa = standard error of a.  b = raw coefficient for the association between the mediator and the outcome (when the predictor is also a predictor of the DV).  sb = standard error of b.

16 Ang & Huan (2012)

17 Ang & Huan (2012) Academic stress Depression Suicidal Ideation

Mediation Model Ang & Huan (2006)

Strength of Mediated Effect Sobel Test- Indicated if change in academic stress Bs from Path c to path c’ is statistically significant Shrout & Bolger (2002)  Proportion of relation of academic stress to suicide ideation that is mediated by depression  Calculated from the unstandardized Bs for paths ab& c; requires a sample size of about 500  ab/c = ( ) ( )/ ( ) = ( ) / ( ) =.7390 = 74%

Strength of Mediated Effect Sobel Test- Indicated if change in academic stress Bs from Path c to path c’ is statistically significant Shrout & Bolger (2002)  Proportion of relation of academic stress to suicide ideation that is mediated by depression  ab/c = (.12) (2.71)/.44 =.3252/.44 =.7390 = 74%