Bureau of Labor Statistics
This site is an excellent resource for students to explore trends in earnings, and to consider what factors may affect wages among workers and professions.
Environmental Protection Agency (EPA)
This site looks at the concept of causation, and considers its role in studying environmental phenomenon.
World Health Organization
This website provides a useful look at how the World Health Organization identifies and studies possible risks and environmental factors which tend to cause higher disease burdens in developing countries. This site would make a useful resource for a possible class assignment.
National Heart, Lung, and Blood Institute
This site examines variables which tend to cause individuals to be overweight and/or obese, and provides a good starting point to help students consider what control variables they would want to study in order to better understand this important health issue.