Table 2.

The five stages of the processing, replication, imputation, merging and evaluation to prepare individual participant data for meta-analysis guidelines, and actions involved at each stage

Stage	Actions
1. Processing	Standardising the data to a preferred format, typically based on the statistical software package that is chosen for data manipulation. Verification of the data, recoding of variables of interest and harmonisation of scales of measurement. Checking sample size and key descriptive data is recommended as a useful initial step at this stage.
2. Replication	Replication of published data tables (e.g. baseline characteristics table) ensures that the processed datasets are consistent with the data that have been analysed for previously published reports.
3. Imputation	Imputation of missing data may be considered, depending on the stated research question, before or after merging data into a single harmonised dataset.
4. Merging	Data are merged into a single harmonised dataset.
4. Evaluation	Evaluation of data heterogeneity and distribution can then be explored prior to the planned pooled analysis, to inform selection of appropriate analytic methods.