Read Case Study V: Retrospective Cohort Study of The Association of Congential Malformations and Hazardous Waste on pages 374-378 of your text and discuss the following:

1. What are controls in a research study and how are they used? How are controls used in this study?

2. What are confounding variables and how do they affect a research study? What are the problems and limitations of confounding variables in this study?