Abstract
Claims that effort increases cognitive scores are now under great doubt. What is needed is randomized controlled trials optimized for testing causal influence and avoiding confounding of self-evaluation of performance with feelings of good effort. Here we report three large studies using unconfounded measures of effort and instrumental analysis to isolate any causal effect of effort on cognitive score. An initial study (N = 393) validated an appropriate effort measure, demonstrating excellent external and convergent validity (β = .61). Study 2 (N = 500, preregistered) randomly allocated subjects to a performance incentive, using an instrumental variable analysis to detect causal effects of effort. The incentive successfully manipulated effort (𝛽 = .18, p = .001). However, the causal effect of effort on scores was near-zero and non-significant (𝛽 = .04, p = .886). Study 3 (N=1,237) replicated this null result with preregistered analysis and an externally developed measure of effort: incentive again raised reported effort (𝛽 = .17, p <.001), but effort had no significant causal effect on cognitive score (β2 = .27 [-0.07, 0.62]), p = .15). Alongside evidence of research fraud and confounding in earlier studies, the present evidence for the absence of any causal effects of effort on cognitive scores, effort research should shift its focus to goal setting – where effort is useful – rather than raising basic ability, which it appears unable to do.
