Weight-loss surgery and longer life. An article in the Washington Post reported that, according to two large studies, obese people are significantly less likely to die prematurely if they undergo stomach surgery to lose weight. But people choose whether to have stomach surgery. Explain why this fact makes any conclusion about cause and effect untrustworthy. Use the language of lurking variables and confounding in your explanation, and draw a picture like Figure 5.1 to illustrate it.

AppendixLO1