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A peculiar prevalence of p values just below .05
E J Masicampo1, Daniel R Lalande
1Department of Psychology, Wake Forest University, Winston-Salem, NC 27109, USA. masicaej@wfu.edu
Abstract:
In null hypothesis significance testing (NHST), p values are judged relative to an arbitrary threshold for significance (.05). The present work examined whether that standard influences the distribution of p values reported in the psychology literature. We examined a large subset of papers from three highly regarded journals. Distributions of p were found to be similar across the different journals. Moreover, p values were much more common immediately below .05 than would be expected based on the number of p values occurring in other ranges. This prevalence of p values just below the arbitrary criterion for significance was observed in all three journals. We discuss potential sources of this pattern, including publication bias and researcher degrees of freedom.
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