 Thus there seems to be no great barrier to recruiting representative patient samples in ePRO studies.Establishing the validity of an ePRO instrument is in principle no different from that for other methods, such as paper.However most of the instruments in current use have been validated in paper form, and we need to ask (1) whether the paper data can be used to establish validity of the electronic version, and (2) whether data from paper and electronic versions can be used interchangeably.