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Linear Regression Mediating Variables

Mediating Variables

Mediation • 3 variables in a causal sequence • Middle variable is mediator leading to chain of events that

cause a change in DV. Example: • Job affect mediates the influence of competence on

motivation. • What are the 3 variables? • Which one is the IV, DV, Mediator?

IV Mediator DV

competence Affect Motivation

Mediating Variable • Use 7 CFA SDT.sav

• Look at different job levels

• Descriptives, Frequency

• We will look only at Job Level 4 - 6 (Professionals & Specialists, Managers, Executives)

• Select only those with jl>=4

• Participants

– N?

– Age?

– Gender?

– Civil Status?

Mediating Variable

Hypothesis: Job affect mediates the influence of competence on intrinsic motivation.

• Procedures based on Baron & Kinney, 1986 in Tabachnick & Fidell, 2007

• We need to test for paths a, b, c

IV

Mediator

DV

c

a b

Step 1

Path a • Is there a significant relationship between IV and mediator?

(Test path a total effect, what is r?) • If path a is not significant, then there is no mediation • If path a significant, what is β?

IV

Mediator

DV

c

a b

Step 2

Path b • Is there a significant relationship between mediator and DV?

(Test path b, what is r?) • If path b is not significant, then there is no mediation

IV

Mediator

DV

c

a b

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Step 3

Path c • Is there a significant relationship between IV and DV? (Test

path c, what is r?) • If path c is not significant, then there is perfect mediation

IV

Mediator

DV

c

a b

Step 4 Path b' and c' together • Is regression significant? • If so…

– What is β for path b'? – What is β for path c'? (This is also called “direct effect”)

IV

Mediator

DV

c'

a b'

Evaluate mediation

Perfect mediation – Path b' significant – Path c' not significant

IV

Mediator

DV

c'

a b'

Evaluate mediation

No mediation – Path b' not significant – Path c' significant

IV

Mediator

DV

c'

a b'

Evaluate mediation

Partial mediation – Path b' significant – Path c' significant

IV

Mediator

DV

c'

a b'

Interpretation

State the hypothesis Give a brief paragraph discussing if the regression

requirements were met, outliers removed if any, etc. Give an introductory statement that summarizes your

findings before you explain the detailed results.

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Interpretation

Details… - Path from competence to job affect was significant, with r=? - Path from job affect to motivation was significant, with r=? - Path from competence to motivation (total effect) was also

significant, with r=? - When competence and job affect were entered together as

predictors of motivation, competence was not significant (β=?) but affect was significant (β=?)

- Results show that affect (fully? partially?) mediates the influence of competence on motivation.

- The regression was significant, with F(?, ?)=? and p < 0.05. Affect and the indirect effect of competence together explain ? % of the variance in motivation.

Exercise

• Job affect mediates the influence of relatedness on motivation.