In this report, we use fear conditioning research as an example to illustrate the considerable impact of researcher degrees of freedom with respect to exclusion of participants. In human fear conditioning research, the exclusion of substantial numbers of participants as 'non-learners' and 'non-responders' is common - despite a lack of consensus on how to define these groups.We illustrate the substantial heterogeneity in exclusion criteria based on a systematic literature search and highlight

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... ential problems and pitfalls of different definitions through case examples based on re-analyses of existing datasets. Based on this, we propose a consensus on evidence-based rather than idiosyncratic criteria for the definition and treatment of 'non-learners' and 'non-responders' including clear guidelines on reporting details. Taken together, we illustrate how flexibility in data collection and analysis can be avoided in the field of fear conditioning, which will benefit the robustness and replicability of research findings.