Introduction: There is evidence that statistically significant results from observational studies, controlled clinical trials and randomised controlled trials are more likely to be published (publication bias). Furthermore, there is some evidence that published significant results are more likely to be located in prestigious or high-impact journals. Systematic reviews / meta-analyses of individual patient data (IPO) may represent a gold standard of systematic review, giving the best possible summary of current evidence for a particular question. Are they also subject to publication bias?

Objective: To explore the factors associated with publication of IPD meta-analyses, those that determine in which journals they are published and to identify any potential sources of bias.

Methods: The responsible authors of all identified IPD meta-analysis projects in cancer and cardiovascular disease will be surveyed by means of a questionnaire to determine, for example: the reason for selecting a particular journal, the number and the outcome of submission. For the same IPD meta-analyses, the features of these studies that may have influenced if they were published and where they were published will be explored, including: the strength of results, the strength of conclusions, the number of patients, the size of the collaborative group and the journal prestige.

Results: The factors that influence the publication of IPD meta-analyses will be described.