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The Ratcliff diffusion model has proved to be a useful tool in reaction time analysis. However, its use has been limited by the practical difficulty of estimating the parameters. We present a software tool, the Diffusion Model Analysis Toolbox (DMAT), intended to make the Ratcliff diffusion model for reaction time and accuracy data more accessible to experimental psychologists. The tool takes the form of a MATLAB toolbox and can be freely downloaded from ppw.kuleuven.be/okp/dmatoolbox. Using the program does not require a background in mathematics, nor any advanced programming experience (but familiarity with MATLAB is useful). We demonstrate the basic use of DMAT with two examples.
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The Ratcliff diffusion model (RDM) has garnered significant attention in recent years as a model for the simultaneous analysis of reaction time (RT) and accuracy data. There are three main reasons for its popularity. First, it can be applied in many fields (Ratcliff, 1978,1981,1988, 2002; Ratcliff, Gomez, & McKoon, 2004; Ratcliff & Rouder, 1998, 2000; Ratcliff, Thapar, & McKoon, 2004; Ratcliff, Van Zandt, & McKoon, 1999; Strayer & Kramer, 1994; Thapar, Ratcliff, & McKoon, 2003). second, it performs extraordinarily well in terms of parsimony and description of interesting patterns in RT data (see, e.g., Ratcliff, 1987; Ratcliff & Rouder, 1998). Third and finally, its main parameters have interesting process interpretations that allow for substantive insights (Voss, Rothermund, & Voss, 2004). If the RDM has one significant drawback, it is that the model is prohibitively difficult to apply in practice, to the point that methods for fitting the RDM to experimental data are a research topic in their own right (Ratcliff & Tuerlinckx, 2002; Tuerlinckx, Maris, Ratcliff, & De Boeck, 2001; Tuerlinckx, 2004; Vandekerckhove & Tuerlinckx, 2007b; Voss & Voss, in press; Wagenmakers, van der Maas, & Grasman, 2007). Only recently, are attempts being made to render the RDM more applicable in research practice (Vandekerckhove & Tuerlinckx, 2007a, 2007b; Voss & Voss, 2007). This article presents a MATLAB toolbox that is exactly such an attempt.
In the next four sections, we will (1) briefly describe the RDM, (2) repeat the basics of matrix methods in statistical modeling, (3) provide some practical information regarding a new tool, the Diffusion Model Analysis Toolbox (DMAT), and (4)...