Table 3

Important considerations for those planning and undertaking an IMPF project
Rationale & Initiation
 ·  Produce a protocol for the IMPF project prior to its initiation (detailing all aspects of rationale, conduct and statistical analysis) and reference this upon publication of the IMPF
 ·  Consider whether ethics approval is necessary for the IMPF project, and report this upon publication
Process of obtaining IPD
 ·  Report how primary study authors were approached to obtain their IPD
 ·  Report the strategy used for searching the literature for relevant studies (if relevant), including keywords used and databases searched.
 ·  Provide a flowchart showing the search strategy, classification of identified articles, and retrieval of IPD from relevant studies (where relevant)
 ·  Consider how to improve retrieval of IPD from unpublished studies
Details of IPD obtained
 ·  Report number of participants and events for each included study
 ·  Report a summary of the missing data for each study
 ·  Report the reasons why IPD was unavailable for some studies (if relevant), and if possible, report the number of participants, number of events and summary prognostic factor results in such studies
Type and quality of IPD obtained
 ·  Consider and report the quality of studies for which IPD were obtained; in particular, are they all of comparable quality?
Statistical methods used
 ·  Check and report the assumptions of the statistical models used; in particular, do model assumptions appear valid in each study separately?
 ·  Where possible, analyse continuous factors on their continuous scale and consider non-linear trends. Univariate analyses are a good starting point, but a multivariable analysis adjusting for ‘standard’ factors is required to assess the added prognostic value of a factor over ‘established’ factors.
 ·  In multivariable analyses consider carefully which variables can and should be used for adjustment. Sensitivity analyses should be conducted. In a similar way consider how treatment differences can be handled in the analysis.
 ·  In multivariable analyses, define the criteria used to decide whether a factor has independent prognostic value over other factors; also potentially consider whether the interaction between two (or more) prognostic factors is important
 ·  Consider a re-analysis of the IPD in each study as a first or preliminary step toward meta-analysis, to better appreciate the issues within each study first.
 ·  In the meta-analysis, account for clustering of participants within studies (and do not merge IPD and analyse as if IPD all came from a single study) and report how this was done.
 ·  Measure and, if necessary, account for between study heterogeneity in the prognostic factor effect(s) of interest when undertaking meta-analysis
 ·  Where sufficient studies are available (e.g. 10 per covariate of interest) and heterogeneity of estimated effects of interest exists, examine the potential causes of such heterogeneity.
 ·  Consider a sensitivity analysis to assess whether meta-analysis conclusions change when restricting to IPD from the higher quality studies (if relevant)
Assessment of publication bias and availability bias
 ·  Consider the potential impact of publication bias and availability bias on IPD meta-analysis results; in particular, are studies providing IPD comparable to those studies not providing IPD (if relevant)?
Reporting guidelines
 ·  Utilise reporting guidelines for meta-analysis, such as those for MOOSE [24] and IPD meta-analysis [16]

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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