Table 1

Summary of the data extraction form involving 58 questions, which was used to extract information about the 20 IMPF projects examined in detail
Rationale and initiation: We recorded the rationale for the IMPF, and whether there was mention of a project protocol and ethics approval.
Process of obtaining IPD: We recorded how researchers identified relevant primary studies (e.g. systematic review, coalition of research groups); how they decided which studies to seek IPD from; the process of obtaining IPD; and problems encountered.
Details of IPD obtained: We recorded the proportion of studies providing IPD; the total number of participants in the IPD; whether the number of participants and events were reported for each IPD study; whether there was any missing data problems; and whether there was variability in how prognostic factors were measured.
Type and quality of IPD studies: We recorded the design (e.g. cohort, randomised trials) of studies providing IPD; whether they were published or unpublished; and whether they were assessed for their quality and, if so, how.
Statistical methods used: We recorded whether a statistical methods section was provided; the statistical models used in the meta-analysis (e.g. Cox regression, logistic regression); and how some specific statistical issues were addressed (such as clustering of participants within studies; between-study heterogeneity in prognostic factor effects; and the analysis of continuous prognostic factors).
Assessment of publication bias and availability bias: We recorded if and how researchers examined the potential impact of publication bias (studies unpublished due to non-significant prognostic results) or availability bias (studies providing IPD are a biased portion of the studies from which IPD was desired) in their meta-analysis.
Adherence to reporting guidelines: As a crude measure of adherence to reporting guidelines for meta-analysis, we recorded how many of the articles referenced the reporting guidelines of either MOOSE [24] or QUORUM [25].
Limitations and challenges of an IMPF: We catalogued all the problems that hindered the IMPF approach as reported by the researchers.

Abo-Zaid et al.

Abo-Zaid et al. BMC Medical Research Methodology 2012 12:56   doi:10.1186/1471-2288-12-56

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