Having access to the ‘raw’ data for each study enables checking, thorough exploration, and re-analysis of the data in a consistent way. Thus, one does not have to rely on interpreting information and analyses presented in published reports, be constrained by summary data provided in tabular format, or be forced to consider combining the summary statistics from studies that have been calculated in different ways. It also avoids problems with the original analyses; for example it might be possible to carry out analyses according to intention-to-treat principles, even if the original trial analyses did not do this.