Mplus code for mediation, moderation, and moderated mediation models

Model 7 (latent variable version): 1 or more mediators, in parallel if multiple (example uses 1), 1 moderator of IV-Mediator path only

Example Variables: 1 latent predictor X measured by 4 observed variables X1-X4, 1 latent mediator M measured by 4 observed variables M1-M4, 1 latent moderator W measured by 4 observed variables W1-W4, 1 latent outcome Y measured by 4 observed variables Y1-Y4

Preliminary notes:

The code below assumes that

  • The latent IV (factor X) is measured by continuous observed variables X1-X4.
  • Any latent moderator(s) (factors W, V, Q, Z) are measured by continuous observed variables W1-W4, Z1-Z4, V1-V4, Q1-Q4 respectively.
  • Any latent mediator(s) (factor M, or factors M1, M2, etc.) are measured by continuous observed variables M1-M4 or M1_1-M1-4, M2_1-M2_4 respectively.
  • The latent outcome Y is measured by continuous observed variables Y1-Y4.

 

Model Diagram (factor indicator variables omitted for space/clarity reasons):

 

Statistical Diagram (factor indicator variables omitted for space/clarity reasons):

 

Model Equation(s):

Y = b0 + b1M + c'X
M = a0 + a1X + a2W + a3XW

 

Algebra to calculate indirect and/or conditional effects by writing model as Y = a + bX:

Y = b0 + b1M + c'X
M = a0 + a1X + a2W + a3XW


Hence... substituting in equation for M

Y = b0 + b1(a0 + a1X + a2W + a3XW) + c'X


Hence... multiplying out brackets

Y = b0 + a0b1 + a1b1X + a2b1W + a3b1XW + c'X


Hence... grouping terms into form Y = a + bX

Y = (b0 + a0b1 + a2b1W) + (a1b1 + a3b1W + c')X


Hence...

One indirect effect(s) of X on Y, conditional on W:

a1b1 + a3b1W = (a1 + a3W)b1

One direct effect of X on Y:

c'

 

Mplus code for the model:

! Latent predictor variable X measured by X1-X4
! Latent mediator M measured by 4 observed variables M1-M4
! Latent moderator W measured by 4 observed variables W1-W4
! Latent outcome variable Y measured by Y1-Y4

USEVARIABLES = X1 X2 X3 X4 M1 M2 M3 M4
W1 W2 W3 W4
Y1 Y2 Y3 Y4;

ANALYSIS:
   TYPE = GENERAL RANDOM;
   ESTIMATOR = ML;
   ALGORITHM = INTEGRATION;

! In model statement first state measurement model
! Then create any latent interactions required
! Then state structural model naming each path and intercept using parentheses

MODEL:

! Measurement model
! Identify moderator factors by fixing variance = 1 (instead of first loading)
! This makes these factors standardised
   X BY X1 X2 X3 X4;
   M BY M1 M2 M3 M4;
   W BY W1* W2 W3 W4;
   Y BY Y1 Y2 Y3 Y4;

    W@1;

! Create latent interactions
   XW | X XWITH W;

! Fit structural model and name parameters
! Note that intercepts of M, Y are fixed = 0 since they are latent vars
! so no code to state and name them as parameters
   Y ON M (b1);

   Y ON X (cdash);

   M ON X (a1);
   M ON W (a2);
   M ON XW (a3);

! Use model constraint subcommand to test conditional indirect effects
! You need to pick low, medium and high moderator values for W
! for example, of 1 SD below mean, mean, 1 SD above mean

! 1 moderator, 3 values for it
! arbitrary naming convention for conditional indirect and total effects used below:
! MED_Q = medium value of Q, etc.

MODEL CONSTRAINT:
    NEW(LOW_W MED_W HIGH_W
    IND_LOWW IND_MEDW IND_HIW
    IMM
    TOT_LOWW TOT_MEDW TOT_HIW);

    LOW_W = -1;   ! -1 SD below mean value of W
    MED_W = 0;   ! mean value of W
    HIGH_W = 1;   ! +1 SD above mean value of W

! Calc conditional indirect effects for each combination of moderator values
! and index of moderated mediation

    IND_LOWW = a1*b1 + a3*b1*LOW_W;
    IND_MEDW = a1*b1 + a3*b1*MED_W;
    IND_HIW = a1*b1 + a3*b1*HIGH_W;

    IMM = a3*b1;

! Calc conditional total effects for each combination of moderator values

    TOT_LOWW = IND_LOWW + cdash;
    TOT_MEDW = IND_MEDW + cdash;
    TOT_HIW = IND_HIW + cdash;

! Use loop plot to plot conditional indirect effect of X on Y for each combination of low, med, high moderator values
! Could be edited to show conditional direct or conditional total effects instead
! NOTE - values from -3 to 3 in LOOP() statement since
! X is factor with mean set at default of 0

    PLOT(LOMOD MEDMOD HIMOD);

    LOOP(XVAL,-3,3,0.1);

    LOMOD = IND_LOWW*XVAL;
    MEDMOD = IND_MEDW*XVAL;
    HIMOD = IND_HIW*XVAL;

PLOT:
   TYPE = plot2;

OUTPUT:
   STAND CINT;

 

Return to Model Template index.

To cite this page and/or any code used, please use:
Stride C.B., Gardner S., Catley. N. & Thomas, F.(2015) 'Mplus code for the mediation, moderation, and moderated mediation model templates from Andrew Hayes' PROCESS analysis examples' , http://www.figureitout.org.uk

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