Once primary investigators have agreed to collaborate, the next step is to provide clear instructions on what data they need to supply and on any preferred data format. The project team should be prepared to accept data in whatever format is most convenient for those supplying it, whether that is electronically, as printouts, or on paper forms, and should be prepared to recode information as necessary. However, although the early IPD meta-analyses in the 1980s relied heavily on data being supplied on paper, most information is now supplied by e-mail or on disk, and investigators are often willing to transform or code their data according to the specified format.