Selective Hypothesis Reporting in Psychology: Comparing Preregistrations and Corresponding Publications

This study assesses the extent of selective hypothesis reporting in psychological research by comparing the hypotheses found in a set of 459 preregistrations to the hypotheses found in the corresponding papers. We found that more than half of the preregistered studies we assessed contain omitted hypotheses (N = 224; 52.2%) or added hypotheses (N = 227; 56.8%), and about one-fifth of studies contain changed hypotheses (N = 82; 19%). We found only a small number of studies with demoted hypotheses (N = 2; 1%) and no studies with promoted hypotheses. In all, 59% of studies include at least one hypothesis in one or more of these categories, indicating a substantial bias in presenting and selecting hypotheses by researchers and/or reviewers/editors. Contrary to our expectations, we found that added hypotheses and changed hypotheses were not more likely to be statistically significant than non-selectively reported hypotheses. For the other types of selective hypothesis reporting, no powerful test of the relationship with statistical significance could be carried out. Finally, we found that replication studies were less likely to include selectively reported hypotheses than original studies. Thus, selective hypothesis reporting is problematically common in psychological research and may partly be explained by the fact that authors do not specifically and clearly enough formulate hypotheses in preregistrations and papers. We urge researchers, reviewers, and editors to ensure that hypotheses outlined in preregistrations are clearly formulated and accurately presented in the corresponding papers.