Diffusion-model data analysis permits disentangling different processes underlying the effects of experimental manipulations. Estimates can be provided for the speed of information accumulation, for the amount of information used to draw conclusions, and for a decision bias. One parameter describes the duration of non-decisional processes including the duration of motor-response execution. In the standard diffusion model, it is implicitly assumed that both responses are executed with the same speed. In some applications of the diffusion model, this assumption will be violated. This will lead to a bias of parameter estimates. Consequently, we suggest accounting explicitly for differences in the speed of response execution for both responses. Results from a simulation study illustrate that parameter estimates from the standard model are biased if the speed of response execution differs between responses. A second simulation study shows that large trial numbers (N>1000) are needed to detect whether differences in response-execution times are based on different execution times
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