Finally, there are practical aspects to consider before committing to a data set.
Access and Cost: Is the data set publicly available, or does it require a special application and/or payment? Some restricted data sets may have long waiting periods for approval, which could delay your dissertation and therefore use of restricted data sets is discouraged.
Data Structure and Size: How is the data organized? Is it a single file or a complex series of files that need to be merged? Is the data set so large that it requires specialized computing resources you may not have access to?
Previous Research: Has the data set been widely used in your field? If so, you will need to find a unique angle or research question to avoid duplicating existing work. On the other hand, a data set that has been extensively used often indicates that it is well-regarded and reliable.