Does the level of precipitation predict violence? Dubner and Levitt (2006b) reported on various studies that found links between rain and violence. They mentioned one study by Miguel, Satyanath, and Sergenti that found that decreased rain was linked with an increased likelihood of civil war across a number of African countries they examined. Referring to the study's authors, Dubner and Levitt state, "The causal effect of a drought, they argue, was frighteningly strong."

a. What is the independent variable in this study?

b. What is the dependent variable?

c. What possible third variables might play a role in this connection? That is, is it just the lack of rain that's causing violence, or is it something else?