med4way

A Stata command for the 4-way decomposition using parametric regression models

• Current version: 2.3.2
• Release date: 30sep2021

---

Description

med4way uses parametric regression models to estimate the components of the 4-way decomposition of the total effect of an exposure on a outcome in the presence of a mediator with which the exposure may interact. This decomposition breaks down the total effect of the exposure on the outcome into components due to mediation alone, to interaction alone, to both mediation and interaction, and to neither mediation nor interaction.

med4way provides standard errors and confidence intervals for the estimated components using the delta method (default) or the bootstrap.

med4way allows continuous, binary, count or survival outcomes, and continuous or binary mediators.

Further details can be found in Discacciati et al. (2018) and in the help file.

Note: the 4-way decomposition holds without any assumptions about confounding. However, to interpret each of the components causally does require assumptions about confounding. See VanderWeele (2014) for a detailed exposition of those assumptions.

How to cite

If you use med4way, please cite this paper:

Discacciati, A., Bellavia, A., Lee, J.J., Mazumdar, M., Valeri, L. Med4way: a Stata command to investigate mediating and interactive mechanisms using the four-way effect decomposition. International Journal of Epidemiology. 2019 Feb;48(1):15-20. doi: 10.1093/ije/dyy236

Installation

• To install the current version of med4way directly from GitHub, run:

net install med4way, from("https://raw.githubusercontent.com/anddis/med4way/master/") replace

from within a web-aware Stata (version 13+).

• For older versions of Stata, download and extract the zip file and then run:

net install med4way, from(mydir) replace 

from within Stata, where mydir is the directory that containes the extracted files.

• After installation, see the help file:

help med4way

• To download in the current working directory the datasets needed to run the example code in the help file, type:

net get med4way, from("https://raw.githubusercontent.com/anddis/med4way/master/")

Authors

Andrea Discacciati (1), Andrea Bellavia (2,3), Linda Valeri (4)

(1) Unit of Biostatistics, Karolinska Institutet, Stockholm, Sweden (2) Department of Environmental Health, Harvard T.H. Chan School of Public Health, Boston, MA, USA (3) Department of Biostatistics, Harvard T.H. Chan School of Public Health, Boston, MA, USA (4) Department of Biostatistics, Columbia University Mailman School of Public Health, New York, NY, USA

References

Discacciati, A., Bellavia, A., Lee, J.J., Mazumdar, M., Valeri, L. Med4way: a Stata command to investigate mediating and interactive mechanisms using the four-way effect decomposition. International Journal of Epidemiology. 2019 Feb;48(1):15-20. doi: 10.1093/ije/dyy236

VanderWeele, T.J. A unification of mediation and interaction: a 4-way decomposition. Epidemiology. 2014 Sep;25(5):749-61.