Collecting data at the level of the individual participant enables translation between different staging, grading, ranking or other scoring systems, and may therefore allow pooling of data from studies that would not otherwise be possible, because of differences between the data collection tools. To allow this, it is important that the appropriate data are sought (see Section 18.3.1) and that the data supplied are recoded or transformed to reflect common definitions. For example, if the outcome of interest is pre-eclampsia, data on blood pressure and proteinurea would need to be collected and considered together to define whether the pre-eclampsia (according to the review protocol definition) had been observed.