rticipants would be designated by a single ID in each data collection system. In practice, unfortunately, this is often not possible due to limitations of the systems used. As a result, researchers are forced to deal with the fact that participants are known under different IDs in each system. With a key-file, data can be tied together through scripts.</p>
<p>In the example key-file below, we find four columns. The first column defines the global study ID for each participant (i.e., the ID that the research