The NACJD includes a variety of data resource guides on its home page; http://www.icpsr.umich.edu/icpsrweb/NACJD/
Each resource guide describes how a data series is collected, along with key features of measures and other information. Choose two data resource guides, and then: (a) summarize in a paragraph or so how data were collected, and what are the units of analysis; and (b) formulate at least one research question that you think can be addressed by data in the series.