Checking for missing or duplicated data

When data are received, it is important to check these as soon as possible to ensure that they can be read and loaded into the central analysis system. For example, if the data arrive as email attachments, it should be checked that the files can be opened and that the information is for the correct study. At this stage it is useful to confirm that data have been received for all appropriate (usually all randomized) individuals, checking that the numbers supplied are consistent with any publications or other information and that, for example, there are no obvious omissions or duplicates in the sequence of patient record or study identifier numbers.