HIV cohort collaborations: proposal for harmonization of data exchange.

HIV cohort studies have provided useful information on the natural history of HIV infection and the effects of antiretroviral therapy. It has become increasingly common to combine data from several cohorts into one dataset in order to address certain specific questions with more statistical power than can be achieved with the individual studies. This requires each cohort to map data into a standard format before merging. Until recently, this standard format has differed for each such collaborative analysis. We have therefore developed the HIV Cohort Data Exchange Protocol (HICDEP), which is freely available at http://www.cphiv.dk/HICDEP.pdf. Once individual cohorts have set up a means of transfering data into this format, as and when required, this should greatly facilitate data merging for future joint analyses. The HICDEP incorporates data from HIV drug resistance tests, which have been particularly challenging for cohorts to integrate into databases.