Table 2 Methodology of meta-analysis

Protocol development

   Definition of population, intervention and outcomes

   Specification of data sources and selection criteria

Search strategy

   Adequate comprehensiveness

   Sources and techniques

   Language restrictions

Study selection

   A priori criteria

   Justification of exclusions

Methodologic quality assessment

   Basis for inclusion, explanation of heterogeneity or sensitivity

analyses

   Minimization of bias

   Quality scoring system

Data extraction

   Specification of data to be extracted

   Avoidance of bias

   Inclusion of all relevant data

Analysis

   Appropriate model (fixed versus random effects)

   Effect size (eg relative risk, odds ratio, risk difference)

   Precision (confidence intervals)

   Evaluation of heterogeneity

   Subgroup analyses

   Sensitivity analyses