Abstract
In the recent years, there is a growing interest to use the Ratcliff Diffusion Model (1978) for diagnostic purposes as the parameters of the model capture interindividual differences in specific cognitive processes. The parameters are estimated using reaction time data from binary classification tasks. For a potential diagnostic application of parameter values sufficient reliability is a necessary precondition. In two studies, each with two sessions separated by 1 week, the retest reliability of the diffusion model parameters was assessed. In Study 1, 105 participants completed a lexical decision task and a recognition memory task. In Study 2, 128 participants worked on an associative priming task. Results show that the reliability of the main parameters of the Ratcliff Diffusion Model (in particular of the speed of information accumulation and the threshold separation with rs > 0.70 for all three tasks) is satisfying. Besides, we analyzed the influence of the number of trials on the retest reliability using different estimation methods (Kolmogorov–Smirnov, Maximum Likelihood, Chi-square and EZ) and both empirical and simulated datasets.
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Notes
Noteworthy, in unpublished studies from our lab, we failed to find correlations of threshold separation with self-reported impulsivity using standard speeded response time tasks (cf. also Stahl et al., 2014). However, when using more difficult tasks that required a long duration of information accumulation (RT > 5 s) weak to moderate correlations emerged.
Words had frequencies below 5 per million (CELEX; Baayen, Piepenbrock, & Gulikers, 1995) and—at the same time—a frequency class of 14 or 15 (online dictionary project of the university of Leipzig in November 2014, see http://wortschatz.unileipzig.de), indicating that the word “der” (“the”) is used 214 or 215 times as often in German language as our stimuli.
As EZ cannot be applied to datasets with an accuracy rate of 100 %, we applied an edge correction method which has also been used by Wagenmakers et al. (2007): \({\text{accuracy}} = 1 - \frac{1}{2 \times n}\), with n being the number of trials. Similarly, in Study 3 we additionally used a correction for a few datasets due to an observed accuracy of 50 % in one condition (\({\text{accuracy}} = 0.5 + \frac{1}{2 \times n}\)).
In each condition, fast-dm requires at least 10 trials (independent of the type of response) for ML and KS estimation and 12 trials (of the same response) for CS estimation (Voss et al., 2015). Thus, for the data of the APT due to the higher number of conditions no retest coefficients could be computed for 32 trials and for CS neither for 48 trials.
Construct-samples is part of fast-dm (Voss et al., 2015). For the simulation of datasets we used a high precision setting of p = 4.
Note that, as already mentioned, it is possible that the contamination in the empiric data is different from the type and amount of contamination that we assumed for the simulation of data. Thus, it could be that the estimation of the drift rate suffers less from contamination than for example the estimation of t 0 and that not (only) the stability of the parameters is responsible for the different distances between the lines of simulated and empiric data. Our study, thus, only allows getting an approximate idea of the state proportions. A clear disentangling of state and trait proportions would require larger samples of participants and data points.
Results are very similar for Session 2.
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This research was supported by a Grant from the German Research Foundation to Andreas Voss (Grant No. VO1288/2-1).
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Lerche, V., Voss, A. Retest reliability of the parameters of the Ratcliff diffusion model. Psychological Research 81, 629–652 (2017). https://doi.org/10.1007/s00426-016-0770-5
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DOI: https://doi.org/10.1007/s00426-016-0770-5