Stata FAQ
How can I do moderated mediation in Stata?

Preacher, Rucker and Hayes (2007) and updated in Hayes (2013) show how to do moderated mediation using an SPSS macro, so how can I do moderated mediation in Stata?

Here are the full citations:

Hayes, A.F. (2013) Introduction to Mediation, Moderation, and Conditional Process Analysis: A Regression-Based Approach. New York, NY: Guilford Press

Preacher, K.J., Rucker, D.D. and Hayes, A.F. (2007). Addressing moderated mediation hypotheses:
      Theory, methods, and prescriptions. Multivariate Behavioral Research, 42(1), 185-227.


We will begin with a few definitions. A mediator variable is a variable that sits between an independent variable and the dependent variable such that some of the effect of the independent variable on the dependent variable passes through the mediator variable. This is known as the indirect effect.

A moderator variable is a variable involved in an interaction with another variable in the model such that the effect of the other variable depends upon the value of the moderator variable, i.e., the effect of the other variable changes depending on the value of the moderator.

Moderated mediation occurs when a moderator variable interacts with a mediator variable such that the value of the indirect effect changes depending on the value of the moderator variable. This is known as a conditional indirect effect, i.e., the value of the indirect effect is conditional on the value of the moderator variable.

Hayes (2013) and Preacher et al (2007) provide the theoretical background and framework for moderated mediation. They also provide an SPSS script that computes conditional indirect effects and their standard errors in two different ways. It is not all that difficult to compute the indirect effects. On the other hand, standard errors are much more complicated.

The first method in Preacher et al is normal theory based. This method is fairly efficient but suffers from the fact that the distribution of conditional indirect effects are known to be nonnormal, most usually skewed and kurtotic. Confidence intervals and hypothesis tests using normal theory based approaches are not recommended for final models in your research.

The second approach is to use bootstrapping to obtain standard errors and confidence intervals. Although this approach can be much slower the standard errors are not normal theory based. In particular, the biased corrected and percentile confidence intervals are nonsymmetric and better reflect the sampling distribution of the conditional indirect effects.

The remainder of this FAQ page is devoted to showing how to compute conditional indirect effects, standard errors and confidence intervals using Stata. We will show an example for each of the five models from Preacher et al. For each model there is a section using a normal theory based approach that uses sem and nlcom. Also, for each of the models we will show how to obtain the bootstrap estimates of standard errors and confidence intervals.

In order to compute the conditional indirect effects we need to have access to regression coefficients from two different models; one model with the mediator as the response variables and another model with the dependent variable as the response variable. The easiest way to do this in Stata is to use the sem command introduced in Stata 12. When set up correctly, it will have all of the coefficients that we need. In configuring the sem command, all the effects from the mediator variable to the left will go into the first sem equation, while everything from the dependent variable to the left goes into the second sem equation. We will make use of the sem for both the normal based estimation and for bootstrapping.

Conditional indirect effects are obtained by multiplying coefficients from the sem model along with selected values of the moderator variable. For four of the five models, we will compute the conditional indirect effects for three different values of the moderator variable; mean(m1) - 1 sd(m1) {low moderator}, mean(m1) {medium moderator}, mean(m1) + 1 sd(m1) {high moderator}. For model 4 there will be nine combinations of moderator values because the are two moderator variables in the model. Each of the three levels of the first moderator are used in combination with the three levels of the second moderator variable thus yielding the nine combinations.

For the normal based approach we use the nlcom command to compute the conditional indirect effects and their standard errors. nlcom uses the delta method to obtain the standard errors. Each coefficient in the sureg model is identified in nlcom using both the equation name (generally the response variable for that equation) and the predictor name. Thus, in a model with read as the response variable and math as the predictor, the coefficient would by entered as [read]_b[math].

Before trying any of the models, run the Stata code below to read in the data and to rename the variables to be consistent with the variable names in the images of the models. The simplified naming also assists in quickly recognizing the role of each variable in the model.

use http://www.ats.ucla.edu/stat/data/hsb2, clear
rename science y  /* dependent variable   */
rename math x     /* independent variable */
rename read m     /* mediator variable    */
rename write w    /* moderator variable 1 */
rename socst z    /* moderator variable 2 */
Click on the image of the model you want to go to.

Model 1


Model 2


Model 3


Model 4


Model 5


Model 1 (Hayes, 2013 Model 74)

Model 1 illustrates the situation in which the independent variable is also the moderator variable which effects the path between the mediator and the dependent variable.

Formulas:

m = a0 + a1x
y = b0 + b1m + b2x + b3mx
conditional indirect effect = a1(b1 + b3x)

Normal theory estimation using the delta method for model 1.

quietly summarize x
global m=r(mean)
global s=r(sd)
generate mx=m*x  /*  mv by iv interaction */
sem (m <- x)(y <- m x mx)

Endogenous variables

Observed:  m y

Exogenous variables

Observed:  x mx

Fitting target model:

Iteration 0:   log likelihood = -3585.6581  
Iteration 1:   log likelihood = -3585.6581  

Structural equation model                       Number of obs      =       200
Estimation method  = ml
Log likelihood     = -3585.6581

------------------------------------------------------------------------------
             |                 OIM
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
Structural   |
  m <-       |
           x |    .724807   .0579824    12.50   0.000     .6111636    .8384504
       _cons |   14.07254   3.100201     4.54   0.000     7.996255    20.14882
  -----------+----------------------------------------------------------------
  y <-       |
           m |   .9766164   .2875081     3.40   0.001     .4131109    1.540122
           x |    1.03094   .2969707     3.47   0.001     .4488881    1.612992
          mx |  -.0115869   .0053091    -2.18   0.029    -.0219926   -.0011812
       _cons |  -20.83921   15.16952    -1.37   0.170    -50.57092    8.892495
-------------+----------------------------------------------------------------
     var(e.m)|   58.71925   5.871925                      48.26811    71.43329
     var(e.y)|   49.70994   4.970994                      40.86232    60.47326
------------------------------------------------------------------------------
LR test of model vs. saturated: chi2(1)   =    594.37, Prob > chi2 = 0.0000

nlcom _b[m:x]*(_b[y:m]+($m-$s)*_b[y:mx])            /* mean - 1 sd */

       _nl_1:  _b[m:x]*(_b[y:m]+(52.775-9.47858602138653)*_b[y:mx])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .3442437   .0656135     5.25   0.000     .2156435    .4728439
------------------------------------------------------------------------------

nlcom _b[m:x]*(_b[y:m]+($m)*_b[y:mx])                  /* mean  */

       _nl_1:  _b[m:x]*(_b[y:m]+(52.775)*_b[y:mx])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .2646401   .0516905     5.12   0.000     .1633287    .3659515
------------------------------------------------------------------------------

nlcom _b[m:x]*(_b[y:m]+($m+$s)*_b[y:mx])            /* mean + 1 sd */

       _nl_1:  _b[m:x]*(_b[y:m]+(52.645+9.368447794077296)*_b[y:mx])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1850365   .0614861     3.01   0.003      .064526    .3055469
------------------------------------------------------------------------------
In this example the conditional indirect effect gets smaller as the moderator variable, in this case the independent variable gets larger. Next is the bootstrap code for model 1. The example bootstrap command below uses 500 replications. You will probably want to use at least 1,000 or even 5,000 in real research situations.

capture program drop bootm1
program bootm1, rclass
  sem (m <- x)(y <- m x mx)
  return scalar cielw = _b[m:x]*(_b[y:m]+($m-$s)*_b[y:mx])
  return scalar ciemn = _b[m:x]*(_b[y:m]+($m)*_b[y:mx])
  return scalar ciehi = _b[m:x]*(_b[y:m]+($m+$s)*_b[y:mx])                       
end

bootstrap r(cielw) r(ciemn) r(ciehi), reps(500) nodots: bootm1

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm1
        _bs_1:  r(cielw)
        _bs_2:  r(ciemn)
        _bs_3:  r(ciehi)

------------------------------------------------------------------------------
             |   Observed   Bootstrap                         Normal-based
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .3442437   .0596977     5.77   0.000     .2272384     .461249
       _bs_2 |   .2646401   .0531258     4.98   0.000     .1605154    .3687647
       _bs_3 |   .1850365   .0637424     2.90   0.004     .0601036    .3099693
------------------------------------------------------------------------------

estat boot, bc percentile

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm1
        _bs_1:  r(cielw)
        _bs_2:  r(ciemn)
        _bs_3:  r(ciehi)

------------------------------------------------------------------------------
             |    Observed               Bootstrap
             |       Coef.       Bias    Std. Err.  [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .34424374  -.0027403   .05969768    .2204353    .462091   (P)
             |                                       .2279064   .4661937  (BC)
       _bs_2 |    .2646401  -.0008873    .0531258    .1688669   .3666712   (P)
             |                                        .172691   .3837206  (BC)
       _bs_3 |   .18503645   .0009657   .06374241    .0658211   .3042314   (P)
             |                                       .0620927   .3027444  (BC)
------------------------------------------------------------------------------
(P)    percentile confidence interval
(BC)   bias-corrected confidence interval

Model 2 (Hayes, 2013 Model 8)

In Model 2 the path between the independent variable and the mediator variable is moderated by W.

Formulas:

m = a0 + a1x + a2w + a3xw
y = b0 + b1m + b2x + b3w + b4xw
conditional indirect effect = b1(a1 + a3w)

quietly summarize w
global m=r(mean)
global s=r(sd)
generate wx=w*x  /*  moderator 1 by iv interaction */
sem (m <- x w wx)(y <- m x w xw)

Endogenous variables

Observed:  m y

Exogenous variables

Observed:  x w wx

Fitting target model:

Iteration 0:   log likelihood = -3919.1644  
Iteration 1:   log likelihood = -3919.1644  

Structural equation model                       Number of obs      =       200
Estimation method  = ml
Log likelihood     = -3919.1644

------------------------------------------------------------------------------
             |                 OIM
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
Structural   |
  m <-       |
           x |   .2707428   .3780083     0.72   0.474    -.4701398    1.011625
           w |   .1041694   .3417056     0.30   0.760    -.5655613    .7739002
          wx |   .0044859   .0066954     0.67   0.503    -.0086368    .0176087
       _cons |    19.7711   18.53835     1.07   0.286    -16.56341     56.1056
  -----------+----------------------------------------------------------------
  y <-       |
           m |   .3057916   .0677692     4.51   0.000     .1729665    .4386168
           x |   .7902703   .3627478     2.18   0.029     .0792976    1.501243
           w |   .6316515   .3275671     1.93   0.054    -.0103682    1.273671
          wx |   -.008533   .0064241    -1.33   0.184     -.021124    .0040579
       _cons |  -14.88752   17.81763    -0.84   0.403    -49.80943    20.03438
-------------+----------------------------------------------------------------
     var(e.m)|   52.63581   5.263581                      43.26744    64.03265
     var(e.y)|    48.3477    4.83477                      39.74254    58.81607
------------------------------------------------------------------------------
LR test of model vs. saturated: chi2(0)   =      0.00, Prob > chi2 =      .


nlcom (_b[m:x]+($m-$s)*_b[m:wx])*_b[y:m]            /* mean - 1 sd */

       _nl_1:  (_b[m:x]+(52.775-9.47858602138653)*_b[m:wx])*_b[y:m]

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1421829   .0455118     3.12   0.002     .0529814    .2313843
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m)*_b[m:wx])*_b[y:m]                   /* mean */

       _nl_1:  (_b[m:x]+(52.775)*_b[m:wx])*_b[y:m]

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1551852   .0408543     3.80   0.000     .0751121    .2352582
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m+$s)*_b[m:wx])*_b[y:m]            /* mean + 1 sd */

       _nl_1:  (_b[m:x]+(52.775+9.47858602138653)*_b[m:wx])*_b[y:m]

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1681874   .0451294     3.73   0.000     .0797355    .2566394
------------------------------------------------------------------------------
In this example the conditional indirect effects increase slowly as the value of the moderator variable increases.

Bootstrap code for model 2. The example bootstrap command below uses 500 replications. You will probably want to use at least 1,000 or even 5,000 in real research situations.

capture program drop bootm2
program bootm2, rclass
  sem (m <- x w wx)(y <- m x w wx)
  return scalar cielw = (_b[m:x]+($m-$s)*_b[m:wx])*_b[y:m]
  return scalar ciemn = (_b[m:x]+($m)*_b[m:wx])*_b[y:m]
  return scalar ciehi = (_b[m:x]+($m+$s)*_b[m:wx])*_b[y:m]                       
end

bootstrap r(cielw) r(ciemn) r(ciehi), reps(500) nodots: bootm2

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm2
        _bs_1:  r(cielw)
        _bs_2:  r(ciemn)
        _bs_3:  r(ciehi)

------------------------------------------------------------------------------
             |   Observed   Bootstrap                         Normal-based
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .1421829    .047612     2.99   0.003      .048865    .2355007
       _bs_2 |   .1551852   .0409495     3.79   0.000     .0749256    .2354447
       _bs_3 |   .1681874   .0423557     3.97   0.000     .0851717    .2512031
------------------------------------------------------------------------------

estat boot, bc percentile

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm2
        _bs_1:  r(cielw)
        _bs_2:  r(ciemn)
        _bs_3:  r(ciehi)

------------------------------------------------------------------------------
             |    Observed               Bootstrap
             |       Coef.       Bias    Std. Err.  [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .14218287   .0009392   .04761201    .0579299   .2551758   (P)
             |                                       .0579299   .2551758  (BC)
       _bs_2 |   .15518515   .0001497    .0409495     .078383    .242382   (P)
             |                                        .078383    .242382  (BC)
       _bs_3 |   .16818743  -.0006398   .04235573    .0869211   .2532646   (P)
             |                                        .089544   .2589626  (BC)
------------------------------------------------------------------------------
(P)    percentile confidence interval
(BC)   bias-corrected confidence interval

Model 3 (Hayes, 2013 Model 14)

In Model 3 the path between the mediator variable and the dependent variable is moderated by W.

Formulas:

m = a0 + a1x
y = b0 + b1m + b2x + b3w + b4mw
conditional indirect effect = a1(b1 + b4w)

quietly summarize w
global m=r(mean)
global s=r(sd)
generate mw=m*w  /*  mv by moderator 1 interaction */
sem (m <- x)(y <- m x w mw)

Endogenous variables

Observed:  m y

Exogenous variables

Observed:  x w mw

Fitting target model:

Iteration 0:   log likelihood = -4260.6166  
Iteration 1:   log likelihood = -4260.6166  

Structural equation model                       Number of obs      =       200
Estimation method  = ml
Log likelihood     = -4260.6166

------------------------------------------------------------------------------
             |                 OIM
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
Structural   |
  m <-       |
           x |    .724807   .0579824    12.50   0.000     .6111636    .8384504
       _cons |   14.07254   3.100201     4.54   0.000     7.996255    20.14882
  -----------+----------------------------------------------------------------
  y <-       |
           m |   .8193599   .3169173     2.59   0.010     .1982135    1.440506
           x |     .33696   .0761398     4.43   0.000     .1877287    .4861913
           w |   .6739726   .2880423     2.34   0.019     .1094201    1.238525
          mw |  -.0095993     .00574    -1.67   0.094    -.0208495    .0016509
       _cons |  -17.23954   15.65376    -1.10   0.271    -47.92034    13.44126
-------------+----------------------------------------------------------------
     var(e.m)|   58.71925   5.871925                      48.26811    71.43329
     var(e.y)|   48.10157   4.810157                      39.54022    58.51664
------------------------------------------------------------------------------
LR test of model vs. saturated: chi2(2)   =    639.91, Prob > chi2 = 0.0000

nlcom _b[m:x]*(_b[y:m]+($m-$s)*_b[y:mw])            /* mean - 1 sd */

       _nl_1:  _b[m:x]*(_b[y:m]+(52.775-9.47858602138653)*_b[y:mw])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .2926372   .0700399     4.18   0.000     .1553616    .4299129
------------------------------------------------------------------------------

nlcom _b[m:x]*(_b[y:m]+($m)*_b[y:mw])                   /* mean */

       _nl_1:  _b[m:x]*(_b[y:m]+(52.775)*_b[y:mw])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .2266887   .0524176     4.32   0.000     .1239522    .3294253
------------------------------------------------------------------------------

nlcom _b[m:x]*(_b[y:m]+($m+$s)*_b[y:mw])            /* mean + 1 sd */

       _nl_1:  _b[m:x]*(_b[y:m]+(52.775+9.47858602138653)*_b[y:mw])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1607402   .0612818     2.62   0.009       .04063    .2808504
------------------------------------------------------------------------------
In this example, the conditional indirect effects decreases as the value of the moderator variable increases.

Bootstrap code for model 3. The example bootstrap command below uses 500 replications. You will probably want to use at least 1,000 or even 5,000 in real research situations.

capture program drop bootm3
program bootm3, rclass
  sem (m <- x)(y <- m x w mw)
  return scalar cielw = _b[m:x]*(_b[y:m]+($m-$s)*_b[y:mw])
  return scalar ciemn = _b[m:x]*(_b[y:m]+($m)*_b[y:mw])
  return scalar ciehi = _b[m:x]*(_b[y:m]+($m+$s)*_b[y:mw])                       
end

bootstrap r(cielw) r(ciemn) r(ciehi), reps(500) nodots: bootm3

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm3
        _bs_1:  r(cielw)
        _bs_2:  r(ciemn)
        _bs_3:  r(ciehi)

------------------------------------------------------------------------------
             |   Observed   Bootstrap                         Normal-based
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .2926372   .0666315     4.39   0.000     .1620418    .4232326
       _bs_2 |   .2266887   .0531356     4.27   0.000     .1225448    .3308326
       _bs_3 |   .1607402   .0615717     2.61   0.009     .0400619    .2814185
------------------------------------------------------------------------------

estat boot, bc percentile

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm3
        _bs_1:  r(cielw)
        _bs_2:  r(ciemn)
        _bs_3:  r(ciehi)

------------------------------------------------------------------------------
             |    Observed               Bootstrap
             |       Coef.       Bias    Std. Err.  [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .29263724  -.0008677   .06663153    .1549403   .4144395   (P)
             |                                       .1554288   .4178429  (BC)
       _bs_2 |   .22668872   .0000859   .05313561    .1177044   .3335583   (P)
             |                                       .1170573   .3309805  (BC)
       _bs_3 |    .1607402   .0010394   .06157172    .0423122   .2809089   (P)
             |                                       .0423122   .2809089  (BC)
------------------------------------------------------------------------------
(P)    percentile confidence interval
(BC)   bias-corrected confidence interval

Model 4 (Hayes, 2013 Model 22)

Model 4 has two different moderator variables. One that moderates the path between the independent variable and mediator variable and one that moderates the path between the mediator variable and the dependent variable.

Formulas:

m = a0 + a1x + a2w + a3xw
y = b0 + b1m + b2x + b3w + b4xw + b5z + b6mz
conditional indirect effect = (b1 + b6z)(a1 + a3w)
quietly summarize w
global m1=r(mean)
global s1=r(sd)
quietly summarize z
global m2=r(mean)
global s2=r(sd)
capture generate wx=w*x  /*  moderator 1 by iv interaction */
gen mz=m*z               /*  mv by moderator 2 interaction */
sem (m <- x w wx)(y <- m x w wx z mz)

Endogenous variables

Observed:  m y

Exogenous variables

Observed:  x w wx z mz

Fitting target model:

Iteration 0:   log likelihood = -6096.1477  
Iteration 1:   log likelihood = -6096.1477  

Structural equation model                       Number of obs      =       200
Estimation method  = ml
Log likelihood     = -6096.1477

------------------------------------------------------------------------------
             |                 OIM
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
Structural   |
  m <-       |
           x |   .2707428   .3780083     0.72   0.474    -.4701398    1.011625
           w |   .1041694   .3417056     0.30   0.760    -.5655613    .7739002
          wx |   .0044859   .0066954     0.67   0.503    -.0086368    .0176087
       _cons |    19.7711   18.53835     1.07   0.286    -16.56341     56.1056
  -----------+----------------------------------------------------------------
  y <-       |
           m |   .4013056    .282893     1.42   0.156    -.1531546    .9557658
           x |   .7571766   .3864076     1.96   0.050    -.0001684    1.514522
           w |   .6031543   .3562554     1.69   0.090    -.0950935    1.301402
          wx |  -.0078215   .0069183    -1.13   0.258     -.021381    .0057381
           z |   .0553245   .2661857     0.21   0.835    -.4663899    .5770389
          mz |  -.0015944   .0050813    -0.31   0.754    -.0115536    .0083647
       _cons |   -17.0724    19.0314    -0.90   0.370    -54.37327    20.22847
-------------+----------------------------------------------------------------
     var(e.m)|   52.63581   5.263581                      43.26744    64.03265
     var(e.y)|   48.28407   4.828407                      39.69024    58.73866
------------------------------------------------------------------------------
LR test of model vs. saturated: chi2(2)   =    571.85, Prob > chi2 = 0.0000

nlcom (_b[m:x]+($m1-$s1)*_b[m:wx])*(_b[y:m]+($m2-$s2)*_b[y:mz])  /* mean1 - 1 sd1; mean2 - 1 sd2 */

_nl_1:  (_b[m:x]+(52.775-9.47858602138653)*_b[m:wx])*(_b[y:m]+(52.405-10.7357934642267)*_b[y:mz])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1557016   .0568792     2.74   0.006     .0442203    .2671828
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m1)*_b[m:wx])*(_b[y:m]+($m2-$s2)*_b[y:mz])  /* mean1; mean2 - 1 sd2 */

_nl_1:  (_b[m:x]+(52.775)*_b[m:wx])*(_b[y:m]+(52.405-10.7357934642267)*_b[y:mz])


------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1699401   .0538198     3.16   0.002     .0644552     .275425
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m1+$s1)*_b[m:wx])*(_b[y:m]+($m2-$s2)*_b[y:mz])  /* mean1 + 1 sd1; mean2 - 1 sd2 */

_nl_1:  (_b[m:x]+(52.775+9.47858602138653)*_b[m:wx])*(_b[y:m]+(52.405-10.7357934642267)*_b[y:mz])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1841786    .059107     3.12   0.002      .068331    .3000263
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m1-$s1)*_b[m:wx])*(_b[y:m]+($m2)*_b[y:mz])  /* mean1 - 1 sd1; mean2 */

_nl_1:  (_b[m:x]+(52.775-9.47858602138653)*_b[m:wx])*(_b[y:m]+(52.405)*_b[y:mz])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1477424     .04785     3.09   0.002     .0539581    .2415267
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m1)*_b[m:wx])*(_b[y:m]+($m2)*_b[y:mz])  /* mean1; mean2 */

_nl_1:  (_b[m:x]+(52.775)*_b[m:wx])*(_b[y:m]+(52.405)*_b[y:mz])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1612531   .0431911     3.73   0.000     .0766001    .2459061
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m1+$s1)*_b[m:wx])*(_b[y:m]+($m2)*_b[y:mz])  /* mean1 + 1 sd1; mean2 */

_nl_1:  (_b[m:x]+(52.775+9.47858602138653)*_b[m:wx])*(_b[y:m]+(52.405)*_b[y:mz])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1747638   .0476804     3.67   0.000      .081312    .2682156
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m1-$s1)*_b[m:wx])*(_b[y:m]+($m2+$s2)*_b[y:mz])  /* mean1 - 1 sd1; mean2 + 1 sd */

_nl_1:  (_b[m:x]+(52.775-9.47858602138653)*_b[m:wx])*(_b[y:m]+(52.405+10.73579
> 34642267)*_b[y:mz])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1397833   .0513566     2.72   0.006     .0391261    .2404404
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m1)*_b[m:wx])*(_b[y:m]+($m2+$s2)*_b[y:mz])  /* mean1; mean2 + 1 sd */

_nl_1:  (_b[m:x]+(52.775)*_b[m:wx])*(_b[y:m]+(52.405+10.7357934642267)*_b[y:mz])


------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1525661   .0486854     3.13   0.002     .0571445    .2479878
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m1+$s1)*_b[m:wx])*(_b[y:m]+($m2+$s2)*_b[y:mz])  /* mean1 + 1 sd1; mean2 + 1 sd */

_nl_1:  (_b[m:x]+(52.775+9.47858602138653)*_b[m:wx])*(_b[y:m]+(52.405+10.7357934642267)*_b[y:mz])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |    .165349   .0534577     3.09   0.002     .0605738    .2701241
------------------------------------------------------------------------------
Bootstrap code for model 4. The example bootstrap command below uses 500 replications. You will probably want to use at least 1,000 or even 5,000 in real research situations.

capture program drop bootm4
program bootm4, rclass
  sem (m <- x w wx)(y <- m x w wx z mz)
  return scalar ciell = (_b[m:x]+($m1-$s1)*_b[m:wx])*(_b[y:m]+($m2-$s2)*_b[y:mz])
  return scalar cieml = (_b[m:x]+($m1)*_b[m:wx])*(_b[y:m]+($m2-$s2)*_b[y:mz])
  return scalar ciehl = (_b[m:x]+($m1+$s1)*_b[m:wx])*(_b[y:m]+($m2-$s2)*_b[y:mz]) 
  return scalar cielm = (_b[m:x]+($m1-$s1)*_b[m:wx])*(_b[y:m]+($m2)*_b[y:mz])
  return scalar ciemm = (_b[m:x]+($m1)*_b[m:wx])*(_b[y:m]+($m2)*_b[y:mz])
  return scalar ciehm = (_b[m:x]+($m1+$s1)*_b[m:wx])*(_b[y:m]+($m2)*_b[y:mz])
  return scalar cielh = (_b[m:x]+($m1-$s1)*_b[m:wx])*(_b[y:m]+($m2+$s2)*_b[y:mz])
  return scalar ciemh = (_b[m:x]+($m1)*_b[m:wx])*(_b[y:m]+($m2+$s2)*_b[y:mz])
  return scalar ciehh = (_b[m:x]+($m1+$s1)*_b[m:wx])*(_b[y:m]+($m2+$s2)*_b[y:mz])
end

bootstrap r(ciell) r(cieml) r(ciehl) r(cielm) r(ciemm) r(ciehm) ///
  r(cielh) r(ciemh) r(ciehh), reps(500) nodots: bootm4

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm4
        _bs_1:  r(ciell)
        _bs_2:  r(cieml)
        _bs_3:  r(ciehl)
        _bs_4:  r(cielm)
        _bs_5:  r(ciemm)
        _bs_6:  r(ciehm)
        _bs_7:  r(cielh)
        _bs_8:  r(ciemh)
        _bs_9:  r(ciehh)

------------------------------------------------------------------------------
             |   Observed   Bootstrap                         Normal-based
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .1557016   .0649863     2.40   0.017     .0283307    .2830725
       _bs_2 |   .1699401   .0621157     2.74   0.006     .0481956    .2916846
       _bs_3 |   .1841786   .0671694     2.74   0.006      .052529    .3158283
       _bs_4 |   .1477424   .0487353     3.03   0.002     .0522231    .2432618
       _bs_5 |   .1612531   .0445524     3.62   0.000     .0739321    .2485741
       _bs_6 |   .1747638   .0493391     3.54   0.000      .078061    .2714666
       _bs_7 |   .1397833   .0492498     2.84   0.005     .0432554    .2363111
       _bs_8 |   .1525661   .0472475     3.23   0.001     .0599627    .2451695
       _bs_9 |    .165349   .0528395     3.13   0.002     .0617855    .2689124
------------------------------------------------------------------------------

estat boot, bc percentile

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm4
        _bs_1:  r(ciell)
        _bs_2:  r(cieml)
        _bs_3:  r(ciehl)
        _bs_4:  r(cielm)
        _bs_5:  r(ciemm)
        _bs_6:  r(ciehm)
        _bs_7:  r(cielh)
        _bs_8:  r(ciemh)
        _bs_9:  r(ciehh)

------------------------------------------------------------------------------
             |    Observed               Bootstrap
             |       Coef.       Bias    Std. Err.  [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .15570156  -.0011114   .06498635    .0403215   .2988805   (P)
             |                                       .0505215   .3103726  (BC)
       _bs_2 |   .16994009  -.0011208   .06211569    .0493589   .2907081   (P)
             |                                       .0592202   .3041216  (BC)
       _bs_3 |   .18417863  -.0011303   .06716942     .056527   .3229917   (P)
             |                                       .0683613   .3390853  (BC)
       _bs_4 |   .14774241  -.0025282   .04873525    .0589332   .2458749   (P)
             |                                       .0740234   .2873931  (BC)
       _bs_5 |    .1612531   -.002414   .04455236    .0787119   .2513106   (P)
             |                                       .0928683   .2640307  (BC)
       _bs_6 |   .17476379  -.0022999   .04933908    .0872108   .2716488   (P)
             |                                       .0949407   .2876344  (BC)
       _bs_7 |   .13978326  -.0039449   .04924982    .0522442   .2376913   (P)
             |                                       .0635381   .2752829  (BC)
       _bs_8 |   .15256611  -.0037072   .04724748    .0625553   .2519639   (P)
             |                                       .0673052   .2589675  (BC)
       _bs_9 |   .16534895  -.0034695   .05283947    .0625117   .2702666   (P)
             |                                       .0756997   .2865739  (BC)
------------------------------------------------------------------------------
(P)    percentile confidence interval
(BC)   bias-corrected confidence interval

Model 5 (Hayes, 2013 Model 59)

Model 5 has a single moderator variable that moderates both the path between the independent variable and mediator variable and the path between the mediator variable and the dependent variable.

Formulas:

m = a0 + a1x + a2w + a3xw
y = b0 + b1m + b2x + b3w + b4xw + b5mw
conditional indirect effect = (b1 + b5w)(a1 + a3w)

quietly summarize w
global m=r(mean)
global s=r(sd)
capture generate wx=w*x   /*  moderator 1 by iv interaction */
capture generate mw=m*w   /*  mv by moderator 1 interaction */
sem (m <- x w wx)(y <- m x w wx mw)

Endogenous variables

Observed:  m y

Exogenous variables

Observed:  x w wx mw

Fitting target model:

Iteration 0:   log likelihood = -5398.1882  
Iteration 1:   log likelihood = -5398.1882  

Structural equation model                       Number of obs      =       200
Estimation method  = ml
Log likelihood     = -5398.1882

------------------------------------------------------------------------------
             |                 OIM
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
Structural   |
  m <-       |
           x |   .2707428   .3780083     0.72   0.474    -.4701398    1.011625
           w |   .1041694   .3417056     0.30   0.760    -.5655613    .7739002
          wx |   .0044859   .0066954     0.67   0.503    -.0086368    .0176087
       _cons |    19.7711   18.53835     1.07   0.286    -16.56341     56.1056
  -----------+----------------------------------------------------------------
  y <-       |
           m |   .7237774   .3852893     1.88   0.060    -.0313758    1.478931
           x |   .5236584   .4351217     1.20   0.229    -.3291644    1.376481
           w |   .7576026   .3460016     2.19   0.029      .079452    1.435753
          wx |  -.0034416   .0078974    -0.44   0.663    -.0189201     .012037
          mw |  -.0077956   .0070744    -1.10   0.270    -.0216612      .00607
       _cons |  -21.81586   18.84366    -1.16   0.247    -58.74876    15.11704
-------------+----------------------------------------------------------------
     var(e.m)|   52.63581   5.263581                      43.26744    64.03265
     var(e.y)|   48.05594   4.805594                      39.50271    58.46113
------------------------------------------------------------------------------
LR test of model vs. saturated: chi2(1)   =    696.37, Prob > chi2 = 0.0000

nlcom (_b[m:x]+($m-$s)*_b[m:wx])*(_b[y:m]+($m-$s)*_b[y:mw])            /* mean - 1 sd */

_nl_1:  (_b[m:x]+(52.775-9.47858602138653)*_b[m:wx])*(_b[y:m]+(52.775-9.47858602138653)*_b[y:mw])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1795967   .0621316     2.89   0.004      .057821    .3013723
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m)*_b[m:wx])*(_b[y:m]+($m)*_b[y:mw])                   /* mean */

_nl_1:  (_b[m:x]+(52.775)*_b[m:wx])*(_b[y:m]+(52.775)*_b[y:mw])

------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1585216   .0411369     3.85   0.000     .0778949    .2391484
------------------------------------------------------------------------------

nlcom (_b[m:x]+($m+$s)*_b[m:wx])*(_b[y:m]+($m+$s)*_b[y:mw])            /* mean + 1 sd */

_nl_1:  (_b[m:x]+(52.775+9.47858602138653)*_b[m:wx])*(_b[y:m]+(52.775+9.47858602138653)*_b[y:mw])


------------------------------------------------------------------------------
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _nl_1 |   .1311629   .0538847     2.43   0.015     .0255509     .236775
------------------------------------------------------------------------------
Bootstrap code for model 5. The example bootstrap command below uses 500 replications. You will probably want to use at least 1,000 or even 5,000 in real research situations.

capture program drop bootm5
program bootm5, rclass
  sem (m <- x w wx)(y <- m x w wx mw)
  return scalar cielw = (_b[m:x]+($m-$s)*_b[m:wx])*(_b[y:m]+($m-$s)*_b[y:mw])
  return scalar ciemn = (_b[m:x]+($m)*_b[m:wx])*(_b[y:m]+($m)*_b[y:mw])
  return scalar ciehi = (_b[m:x]+($m+$s)*_b[m:wx])*(_b[y:m]+($m+$s)*_b[y:mw])                      
end

bootstrap r(cielw) r(ciemn) r(ciehi), reps(500) nodots: bootm5

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm5
        _bs_1:  r(cielw)
        _bs_2:  r(ciemn)
        _bs_3:  r(ciehi)

------------------------------------------------------------------------------
             |   Observed   Bootstrap                         Normal-based
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .1795967   .0731346     2.46   0.014     .0362555    .3229378
       _bs_2 |   .1585216   .0431536     3.67   0.000     .0739422    .2431011
       _bs_3 |   .1311629   .0501183     2.62   0.009     .0329329     .229393
------------------------------------------------------------------------------

estat boot, bc percentile

Bootstrap results                               Number of obs      =       200
                                                Replications       =       500

      command:  bootm5
        _bs_1:  r(cielw)
        _bs_2:  r(ciemn)
        _bs_3:  r(ciehi)

------------------------------------------------------------------------------
             |    Observed               Bootstrap
             |       Coef.       Bias    Std. Err.  [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _bs_1 |   .17959665    .004129   .07313458    .0583385   .3322092   (P)
             |                                       .0600062   .3465318  (BC)
       _bs_2 |   .15852165   .0022404   .04315356    .0775977    .247842   (P)
             |                                       .0758291   .2446393  (BC)
       _bs_3 |   .13116295   .0023994   .05011829    .0406206   .2343201   (P)
             |                                       .0406206   .2343201  (BC)
------------------------------------------------------------------------------
(P)    percentile confidence interval
(BC)   bias-corrected confidence interval

How to cite this page

Report an error on this page or leave a comment

The content of this web site should not be construed as an endorsement of any particular web site, book, or software product by the University of California.