Male Drosophila become sterile when exposed to moderately high temperatures, because sperm are damaged by heat at much lower temperatures than other cells.

Rohmer et al. (2004) asked whether flies from warmer climates are adapted to higher temperatures. They collected flies from France (where it is relatively cool) and India (relatively warm) to test the effects of temperature on sterility. In one procedure, they raised male flies from both locations at a high temperature, 30.5°C, and recorded whether the flies were sterile or fertile. Thirty-two out of 50 flies from France were sterile at this temperature, whereas 20 of 50 flies from India were sterile.

a. Is this an observational or experimental study?

b. Draw a graph to illustrate the association between sterility and source location (India vs. France). What association is suggested?

c. Is there evidence that the populations of flies from these two locations differ in their probability of sterility at this temperature? Do the appropriate hypothesis test.

d. Estimate the relative risk of sterility at this temperature in the Indian population compared to the population in France (consider the Indian population to be the treatment group for this analysis). Include a 95% confidence interval.