Is there bias in the publication of individual patient data meta-analyses?

OBJECTIVE: There is increasing empirical evidence for the existence of bias in the publication of primary clinical research, with statistically significant results being published more readily, more quickly, and in higher impact journals. Meta-analysis of individual patient data (IPD) may represent a gold standard of "secondary" clinical research, giving the best possible summary of current evidence for a particular question, but publication of these may also be subject to bias. This study aimed to explore which factors might be associated with publication of IPD meta-analyses and to identify potential sources of bias. METHODS: For all known IPD meta-analysis projects in cancer, the responsible investigator was surveyed by means of a questionnaire to determine descriptive characteristics of the meta-analysis, the nature of the results, and details of the publication history. RESULTS: There is no good evidence that overall publication status of meta-analyses in cancer is dependent on the statistical or clinical significance of the results. However, those meta-analyses with nonsignificant results did seem to take longer to publish and were published in lower impact journals compared with those with more striking results. CONCLUSIONS: Based on the current data, there seems to be no strong association between the results of IPD meta-analyses in cancer and publication.