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A spurious correlation between difference scores in evidence-accumulation model parameters

Grange, James A.

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Abstract

Evidence-accumulation models are a useful tool for investigating the cognitive processes that give rise to behavioural data patterns in reaction times (RTs) and error rates. In their simplest form, evidence-accumulation models include three parameters: The average rate of evidence accumulation over time (drift rate) and the amount of evidence that needs to be accumulated before a response becomes selected (boundary) both characterise the response-selection process; a third parameter summarises all processes before and after the response-selection process (non-decision time). Researchers often compute experimental effects as simple difference scores between two within-subject conditions and such difference scores can also be computed on model parameters. In the present paper, we report spurious correlations between such model parameter difference scores, both in empirical data and in computer simulations. The most pronounced spurious effect is a negative correlation between boundary difference and non-decision difference, which amounts to r = - .70 or larger. In the simulations, we only observed this spurious negative correlation when either (a) there was no true difference in model parameters between simulated experimental conditions, or (b) only drift rate was manipulated between simulated experimental conditions; when a true difference existed in boundary separation, non-decision time, or all three main parameters, the correlation disappeared. We suggest that care should be taken when using evidence-accumulation model difference scores for correlational approaches because the parameter difference scores can correlate in the absence of any true inter-individual differences at the population level.

Journal Article Type Article
Acceptance Date Aug 9, 2022
Online Publication Date Sep 22, 2022
Publication Date Oct 1, 2023
Publicly Available Date Mar 29, 2024
Journal Behavior Research Methods
Print ISSN 1554-351X
Publisher Springer Verlag
Peer Reviewed Peer Reviewed
Volume 55
Issue 7
Pages 3348-3369
DOI https://doi.org/10.3758/s13428-022-01956-8
Keywords Individual differences, Correlations, Diffusion modelling, RT difference scores
Publisher URL https://link.springer.com/article/10.3758/s13428-022-01956-8

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