Why spend all that time and effort to gather all that data when you can just use someone else's data? It saves SO MUCH time and energy! There's a giant repository of data from researchers across the country called the "ICPSR" (Google it.) There, you can find mountains of data from all kinds of different research in tons of different fields. We can use their data to do our own analyses, saving ourselves time, money, and energy.
The problem is, we need to know how it was collected, how exactly all concepts were operationalized, how variables were constructed, etc. It can be difficult to figure out enough information about someone else's data to convince a responsible researcher that it would be ethical and scientifically valid to use that research for their own ends.
