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A L I S O N BO W L I N G
MODERATION AND MEDIATION IN REGRESSION
MODERATION
• In a 2-way ANOVA• If the interaction is significant we can say that any effect
of one of the IVs on the DV is moderated by the second IV.
• That is, the effect of an IV on the DV differs for different levels of the second IV.
• Follow up by an analysis of simple effects• This analyses the effect of an IV for different levels of the
second IV.
MODERATION IN REGRESSION
• Interactions in regression1. One continuous predictor and one categorical predictor• The effects of the continuous predictor may be assessed at
each level of the categorical predictor2. Two continuous predictors• The effects of one predictor may be assessed at specified
values of the other (moderator) predictor
CENTRING VARIABLES
• It is often useful to centre a variable to facilitate interpretation of the parameters.• Individual predictors represent the effect on the outcome
when the other predictor is zero.• Zero should be meaningful• E.g. in the bird count data, the years were 1981 – 2014.• Year 0 would have been 1981 years ago!• It makes sense to recode (centre) year to range from 0 – 35.• Now year = 0 represents the bird count at the start of the
survey.• For other data, it makes sense to centre a variable at
another value – e.g. the mean.
MBCOPING.SAV
• Investigated the effects of• Gender• Negative life events• Ways of coping• Resilience (cognitive hardiness)• On
• Psychological distress (ghq)
CENTRING AT THE MEAN
• Cognitive hardiness (coghard)• Scores range from 58 – 127• Nobody has zero resilience!• It makes sense to centre
this at the mean.• Create a new variable
coghardc
CONTINUOUS + CATEGORICAL PREDICTORS
• Interaction involving one continuous and 1 categorical variable• Coghardc and Gender ( 2 = female)• Using GLM Univariate….
GENDER X COGHARD INTERACTION
• The effects of cognitive hardiness on ghq differ for males and females.
INTERPRETING THE INTERACTION
Ghq = 48.57 - .65 (Gender) - .43 (Coghardc) - .25 (Gender x Coghardc)
For females ( Gender = 0, reference group)Ghq = 48.57 - .43 (coghardc)
INTERPRETING THE INTERACTION
Ghq = 48.57 - .65 (Gender) - .43 (Coghardc) - .25 (Gender x Coghardc)
For males ( Gender = 1)Ghq = 48.57 - .65(1) - .43 (coghardc) - .25 (1 x coghardc)Ghq = 47.92 - .68 (coghardc)
USING PROCESS (FIELD)• Outcome: ghq
• Model Summary• R R-sq F df1 df2 p• .59 .35 32.96 3.00 183.00 .00
• Model• coeff se t p LLCI ULCI• constant 47.28 2.19 21.58 .00 42.96 51.60• gender .65 1.33 .49 .63 -1.98 3.28• coghardc -.93 .19 -4.84 .00 -1.31 -.55• int_1 .25 .11 2.26 .03 .03 .47
• Interactions:
• int_1 coghardc X gender
• R-square increase due to interaction(s):• R2-chng F df1 df2 p• int_1 .02 5.09 1.00 183.00 .03
• *************************************************************************
• Conditional effect of X on Y at values of the moderator(s):• gender Effect se t p LLCI ULCI• 1.00 -.68 .09 -7.52 .00 -.85 -.50• 2.00 -.43 .07 -6.43 .00 -.56 -.29•
TWO CONTINUOUS VARIABLES
• Effect of Emotional coping (emotcopec) and Cognitive Hardiness on ghq.
Ghq = 47.04 - .33(coghardc) + .22 (emotcopec) - .013 (coghardc x emotcopec)
SCATTERPLOT
Effect of cognitive hardiness on ghq at different levels of emotion coping
EFFECT OF COGHARD ON GHQ
• The effect of cognitive hardiness on ghq depends on emotion coping.• Effect is : -33 - .013 emotcopec
(This is the derivative of Ghq = 47.04 - .33(coghardc) + .22 (emotcopec) - .013 (coghardc x emotcopec)With respect to cognardc
EFFECTS FOR DIFFERENT LEVELS OF EMOTIONAL COPING
• To find the effect (slope) of the predictor (cognitive hardiness) at different levels of the moderator (emotional coping)
Formula is : -33 - .013 emotcopec
Let’s take values of Emotcopec of -10, 0 and + 10
EFFECT OF COGHARD AT DIFFERENT LEVELS OF EMOTCOPE
Effect is : -33 - .013 emotcopec
• Effect of coghard when emotcopec = -10= -.33 - .013 (emotcopec)= -.33 - .013 ( -10)= -.33 + .13= -.20
EFFECT OF COGNITIVE HARDINESS
• Effect of coghard when emotcopec = 0= -.33 - .013 (emotcopec)= -.33 - .013 ( 0)= -.33
• Effect of coghard when emotcopec = 10= -.33 - .013 (emotcopec)= -.33 - .013 ( 10)= -.33 - .13= - .46
USING PROCESS• Outcome: ghq
• Model Summary• R R-sq F df1 df2 p• .64 .41 41.63 3.00 183.00 .00
• Model• coeff se t p LLCI ULCI• constant 47.04 .74 63.65 .00 45.58 48.50• emotco_1 .22 .06 3.47 .00 .10 .35• coghardc -.33 .06 -5.14 .00 -.46 -.21• int_1 -.01 .00 -3.07 .00 -.02 .00
• Interactions:
• int_1 coghardc X emotco_1
• R-square increase due to interaction(s):• R2-chng F df1 df2 p• int_1 .03 9.41 1.00 183.00 .00
• *************************************************************************
• Conditional effect of X on Y at values of the moderator(s):• emotco_1 Effect se t p LLCI ULCI• -12.43 -.17 .09 -1.89 .06 -.35 .01• .00 -.33 .06 -5.14 .00 -.46 -.21• 12.43 -.49 .07 -6.67 .00 -.64 -.35•
MEDIATION
• Mediation occurs when the relationship between a dependent variable and a DV can be explained by their relationship to a third variable (the mediator).
• Barron, R.M and Kenny, D.A. (1986). The moderator-Mediator ….. Journal of Personality and Social Psychology, 51, 1173 - 1182
Independent variable
Dependent variable
Mediator
EMOTION COPING AS A MEDIATOR
• Let us assume that the researcher theorised that emotion coping is a mediator of the effect of cognitive hardiness on ghq.• i.e. that cognitive hardiness influences emotional coping,
and that this influences ghq. • The indirect effect.
• Cognitive hardiness may also influence ghq in addition to its indirect effect• The direct effect
MEDIATION MODEL
Cognitive hardiness ghq
Emotional coping
MEDIATION MODEL IN SPSS
1. Regress emotcope on cognitive hardiness
2. Regress ghq on cognitive hardiness
REGRESSION MODEL IN SPSS
3. Regress ghq on both cognitive hardiness and emotional coping.
COMPLETE MEDIATION MODEL
Cognitive hardiness ghq
Emotional coping
-.596** .23**
-.377**
Cognitive hardiness has both an indirect effect on ghq, and a direct effect on ghq. Indirect effect = -.596 * .23 = -.137
MEDIATION IN AMOS
• Use Amos graphics.• Create the graphic• Read in the SPSS data
file, MBCoping.sav• Go to: View/Set
Analysis Properties…• Click the Output tab• Check: Minimization
history• Check: Standardized
estimates• Check: Squared multiple
correlations
RUN THE ANALYSIS IN AMOS
• The regression weights are the same as those obtained by the regression analysis.
EXAMINE THE OUTPUT (VIEW TEXT)
Regression weights Estimate S.E. C.R. P Label
emotcope <--- coghard -.596 .059 -
10.110 ***
ghq <--- emotcope .232 .064 3.593 ***ghq <--- coghard -.377 .065 -5.842 ***
Unstandardised regression weights Estimate
emotcope <--- coghard -.596ghq <--- emotcope .259ghq <--- coghard -.422
VARIANCES AND R2
R2 Estimate
emotcope .355ghq .375
INDIRECT EFFECT OF COGHARD ON GHQ
Indirect effect coghard emotcopeemotcope .000 .000ghq -.138 .000
Standardized indirect effect coghard emotcope
emotcope .000 .000ghq -.154 .000
MORE COMPLICATED MODELS
MORE COMPLICATED MODELS – REGRESSION WEIGHTS
Estimate S.E. C.R. P Label
emotcope <--- les_neg .100 .107 .936 .349
taskcope <--- les_neg .241 .113 2.131 .033
emotcope <--- coghard -.580 .061 -9.443 ***
taskcope <--- coghard .359 .065 5.513 ***
ghq <--- emotcope .210 .061 3.434 ***
ghq <--- coghard -.304 .066 -4.636 ***
ghq <--- les_neg .425 .090 4.706 ***
ghq <--- taskcope -.051 .058 -.890 .373