title: Indirect evidence of reporting biases was found in a survey of medical research studies.
abstract: OBJECTIVE
  To explore indirect evidence of reporting biases by examining the distribution of P-values reported in published medical articles and to compare P-values distributions across different contexts.
  
  
  METHODS
  We selected a random sample (N = 1,500) of articles published in PubMed in March 2014. We extracted information on study type, design, medical discipline, and P-values for the first reported outcome and primary outcome (if specified) from each article. We plotted the P-values transformed to the z-score scale and used caliper tests to investigate threshold effects.
  
  
  RESULTS
  Out of the 1,500 randomly selected records, 758 (50.5%) were included. We retrieved or calculated 758 P-values for first reported outcomes and 389 for primary outcomes (specified in only 51% of included studies). The first reported and the primary outcome differed in 28% (110/389) of the included studies. The distributions of P-values for first reported outcomes and primary outcomes showed a notable discontinuity at the common thresholds of statistical significance (P-value = 0.05 and P-value = 0.01). We also found marked discontinuities in the distributions of z-scores across various medical disciplines, study designs, and types.
  
  
  CONCLUSIONS
  Reporting biases are still common in medical research. We discuss their implications, strategies to detect them, and recommended practices to avoid them.
authors.affiliation: Centre for Research in Evidence-Based Practice (CREBP), Faculty of Health Science and Medicine, Bond University, 14 University Dr, Robina, Gold Coast, Queensland 4226, Australia. Electronic address: lnb6des@daad-alumni.de.
authors.forename: Loai N
authors.initials: LN
authors.lastname: Albarqouni
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol BS8 2PS, UK.
authors.forename: José A
authors.initials: JA
authors.lastname: López-López
authors.affiliation: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol BS8 2PS, UK.
authors.forename: Julian P T
authors.initials: JPT
authors.lastname: Higgins
mesh_terms: D015982:Bias; D035843:Biomedical Research / Q000592:standards*; D003430:Cross-Sectional Studies; D006801:Humans; D011795:Surveys and Questionnaires
keywords: Bias; Methodology; Publication bias; Reporting bias; p-curve; p-hacking