JAGS diffusion model module

Dominik Wabersich and I have produced a JAGS module for the diffusion model. It is freely available from SourceForge. I recommend the JAGS implementation over the WinBUGS one. There's also a paper.

WinBUGS diffusion model plugin

The WinBUGS diffusion model plugin is a set of Component Pascal functions that implement the first hitting time distribution of a drift diffusion process as a stochastic node in WinBUGS.

The plugin allows the use of the diffusion model as part of a graphical model defined in the BUGS language, providing a flexible integrated modeling framework.

This software is built for Windows systems, but emulation on linux (Ubuntu 11.10 using wine 1.3) has been very successful in limited trials. For a python implementation of the hierarchical diffusion model, see hddm.


In a modified version of WinBUGS, the diffusion model is implemented as a univariate distribution with four or five parameters. Bivariate data (response time and binary response) are represented as univariate by mapping lower boundary hitting times to negative values.

In BUGS code, a stochastic node for the new distribution could be y ~ dwiener(a,ter,z,v), where a is the boundary separation, ter is the non-decision time, z is the starting point, and v is the drift rate.

An optional fifth parameter is the between-trial variability in drift rate. A node for this distribution could look like this: y ~ dwienereta(a,ter,z,v,e), where e is the between-trial standard deviation in drift rate.

The package will be amended in the near future to include example scripts.


The WinBUGS diffusion model plugin is offered free of charge to anyone interested in using diffusion models, provided that you properly cite the software and the associated paper. Requests to use the software for any commercial purpose must be directed to the authors. The WinBUGS diffusion model plugin comes without any warranty of any kind.

The WinBUGS diffusion model plugin is released under the GNU General Public License, which is included in the download archive. A generic version of the GNU GPL can be accessed here.

Download and Installation Instructions

To get the software, proceed to the download arena.

The download package is a ZIP archive containing the entire file structure of BlackBox Component Builder (link), an IDE for Component Pascal. It contains a slightly modified version of WinBUGS 1.4.3 (link) with two new distributions built in. You do not need a previous install of BlackBox or WinBUGS, and if you do have one, the modified version can exist alongside it in a separate directory. There is no installation needed other than extracting the ZIP file.

References and Documentation

Information on how to use the plugin can be found in the following article, including its supplements:

  • Vandekerckhove, J., Tuerlinckx, F., & Lee, M. D. (2011). Hierarchical diffusion models for two-choice response times. Psychological Methods, 16, 44-62. PDFURL

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