Recent attempts to improve on the quality of psychological research focus on good practices required for statistical significance testing. The scrutiny of theoretical reasoning, though superordinate, is largely neglected, as exemplified here in a common misunderstanding of mediation analysis. Although a test of a mediation model X ➔ Z ➔ Y is conditional on the premise that the model applies, alternative mediators Z′, Z″, Z‴ etc. remain untested, and other causal models could underlie the correlation between X, Y, Z, researchers infer from a single significant mediation test that they have identified the true mediator. A literature search of all mediation analyses published in 2015 in Sciencedirect shows that the vast majority of studies neither consider alternative causal models nor alternative mediator candidates. Ignoring that mediation analysis is conditional on the truth of the focal mediation model, they pretend to have demonstrated that Z mediates the influence of X on Y. Recommendations are provided for how to overcome this dissatisfying state of affairs.

In the current article, we test the prediction that an initial bias favoring 1 of 2 equally rewarding options-either based on a genuine contingency or a pseudocontingency in a small sample of initial observations-can survive over an extended period of further sampling from both options, when the reward structure fosters exploitation. Specifically, we argue and demonstrate that in reward-rich environments where two options predominantly-but equally frequently-yield positive outcomes, the initial bias should be upheld because exploitation of the allegedly superior option reinforces the biased preference. In contrast, in reward-impoverished environments, where both options yield predominantly negative outcomes, initial biases can be expected to be eradicated through exploration, which increases the chance of recognizing the equality of the initially nonpreferred option. In 3 experiments, initial evidence in a guided-sampling phase was set up for participants to perceive an actual contingency (Experiment 1) or infer a pseudocontingency (Experiment 2a and b) that made 1 option look more rewarding. In a subsequent free-sampling phase this led to a sustained bias toward this option when the environment contained mostly positive but not when it contained mostly negative outcomes. We argue that biased sampling in reward-rich environments could be responsible for false beliefs about the outcomes of behavioral options, and as such could be relevant to a broad range of topics including social interactions or health contexts.

Why can initial biases persist in repeated choice tasks? Previous research has shown that frequent rewards can lure the decision maker into premature exploitation of a supposedly best option, which can result in the persistence of initial biases. Here, we demonstrate that even in the absence of rewards, initial biases can be perpetuated through a positive testing strategy. After eliciting a biased preference for one of two equally rewarding options, participants (N = 203) could sample freely from both options without the lure of any financial rewards. When participants were told to rule out alternatives in this phase, they explored the supposedly worse option and thereby managed to overcome their initial bias. When told to optimize their strategy, however, they exhibited a positive testing strategy resulting in the continued exploitation of the supposedly better option, a bias they maintained in an incentivized choice phase and later judgments. Across all participants, individual tendencies to exploit one option in earlier phases predicted biased behavior in subsequent phases. The findings highlight that not only the pursuit of instrumental rewards can lead to exploitation and the maintenance of initial biases. We discuss potential consequences for interventions.

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