For this exercise, we will pay special attention to evaluation of confounding in Teitelbaum et al. 2007 . In their study of the association between residential pesticide use and breast cancer, they critically examined the potential confounding role of education. The causal model visually representing the investigators' hypothesis about the effect of education on the pesticide-breast cancer risk is presented below.

Work through this interactive exercise which demonstrates the "mixing of effects" when confounding is present in the data, using the example of coffee drinking as a potential risk factor for low birth weight and the mixing of effects that occurs between coffee drinking and smoking.