MLmed is a computational macro for SPSS that simplifies the fitting of multilevel mediation and moderated mediation models, including models containing more than one mediator. After the model specification, the macro automatically performs all of the tedious data management necessary prior to fitting the model. This includes within-group centering of lower-level predictor variables, creating new variables containing the group means of lower-level predictor variables, and stacking the data as outlined in Bauer, Preacher, and Gil (2006) and their supplementary material to allow for the simultaneous estimation of all parameters in the model.
The output is conveniently separated by equation, which includes a further separation of between-group and within-group effects. Further, indirect effects, including Monte Carlo confidence intervals around these effects, are automatically provided. The index of moderated mediation (Hayes, 2015) is also provided for models involving level-2 moderators of the indirect effect(s).
Users interested in detailed explanations of the models fit using MLmed, as well as example analyses, may find Chapters 5-6 of my Thesis helpful. Note that the User Guide provided within the MLmed download and the link above is more current and thorough than the documentation provided in the appendix of my thesis.
July, 2017 - Updated Beta Version of MLmed now available, which includes a point-and-click interface (see below for updates/bug fixes). It can be downloaded using the link above. The .zip file contains both the MLmed macro (syntax and point-and-click) and the User Guide, which is the same user guide from the previous release. The point-and-click version is not yet documented in the user guide, though the dialog box follows directly from the syntax commands. Once installed, the dialog box is available through Analyze > Mixed Models > MLmed for Multilevel Mediation within SPSS.
Please report any bugs found through email (firstname.lastname@example.org) so I can try to fix them ASAP. Include the SPSS Version number and Operating System when reporting a bug. If an error is encountered while using the point-and-click version, please try the same model using syntax to determine if the issue is with the macro itself, or with the translation from the point-and-click dialog box to the syntax. Also, do not hesitate to email for help. An FAQ section will be constructed when time permits.
The macro was presented at the 2017 APS conference. For now, the corresponding macro citation is:
Rockwood, N. J. & Hayes, A. F. (2017, May). MLmed: An SPSS macro for multilevel mediation and conditional process analysis. Poster presented at the annual meeting of the Association of Psychological Science (APS), Boston, MA. [PDF]
MLmed releases and update overview
MLmed Beta July, 2017 - Current Version (Download link above)
- Fixed mislabeling of the between-group interaction term in moderated multiple mediator models where the within-group moderation was omitted
- Fixed case-sensitivity of outcome and mediator variables in model syntax
- A point-and-click interface
MLmed Beta May, 2017 (Download)