Prevention Science

, Volume 15, Issue 5, pp 611–622 | Cite as

An Exponential Decay Model for Mediation

  • Matthew S. FritzEmail author


Mediation analysis is often used to investigate mechanisms of change in prevention research. Results finding mediation are strengthened when longitudinal data are used because of the need for temporal precedence. Current longitudinal mediation models have focused mainly on linear change, but many variables in prevention change nonlinearly across time. The most common solution to nonlinearity is to add a quadratic term to the linear model, but this can lead to the use of the quadratic function to explain all nonlinearity, regardless of theory and the characteristics of the variables in the model. The current study describes the problems that arise when quadratic functions are used to describe all nonlinearity and how the use of nonlinear functions, such as exponential decay, address many of these problems. In addition, nonlinear models provide several advantages over polynomial models including usefulness of parameters, parsimony, and generalizability. The effects of using nonlinear functions for mediation analysis are then discussed and a nonlinear growth curve model for mediation is presented. An empirical example using data from a randomized intervention study is then provided to illustrate the estimation and interpretation of the model. Implications, limitations, and future directions are also discussed.


Mediation Exponential decay Longitudinal 

Supplementary material

11121_2013_390_MOESM1_ESM.doc (71 kb)
ESM 1 (DOC 71 kb)


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Copyright information

© Society for Prevention Research 2013

Authors and Affiliations

  1. 1.Department of PsychologyVirginia Polytechnic Institute and State University (Virginia Tech)BlacksburgUSA

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