Be specific about your topic so that you can narrow your search, but be flexible enough to tailor your needs to existing sources.
This is what you should be able to define:
Social Unit: This is the population that you want to study.
It can be...
For example: individuals, couples, households
-Organizations and Institutions
For example: companies, political parties, nation states
-Commodities and Things
For example: crops, automobiles, arrests
Time: This is the period of time you want to study.
Things to think about...
-Point in time
A "snapshot" or one-time study
Study changes over time
Keep in mind that there is usually a time lag before data will be published. The most current information available may be a couple years old.
Space: Geography or place.
Examples include political boundaries (nation, state, county, school district, etc.) and census geography (metropolitian statistical areas, tracts, block groups, etc.)
Data is not available for every thinkable topic. Some data is hidden, uncollected, or unavailable. Be prepared to try alternative data.
Be very clear in what you are looking for when talking to a librarian. We are interested in your end goal so be prepared to tell us about your project and what you hope to do. This will save confusion over some questions and give a clear picture on what data you really need.