This site examines the difference between primary and secondary data, and considers how to effectively use data in the course of research. It also looks at the advantages and disadvantages of using secondary data.
The University of Iowa
This presentation by the University of Iowa explores what secondary data analysis is, the reasons for using or not using secondary data, and the sources and types which are available to researchers.
Statistical Abstract of the United States
While the U.S. Bureau of the Census no longer updates data for the Statistical Abstract of the United States since 2011, this site still provides an excellent source of historical data in a variety fields and topics which students may want to explore for their own research needs - particularly in examining trends over a time series.
U.S. Department of Commerce - Bureau of Economic Analysis
This site contains national, international, regional, and industry-specific secondary data sets relating to economic performance that can be consulted. It is a very useful resource for providing raw performance data on a variety of topics.