Which of the following is a natural experiment? Which is more likely to produce a reliable answer? Explain.
a. Elena wants to determine whether rain causes people to drive less. To do so, she compares the amount of gasoline sold on an average day in March in Seattle, Washington (where it rains a great deal), and in Los Angeles, California (where there is much less rainfall).
b. Annika also wants to determine whether rain causes people to drive less. To do so, she compares the amount of gasoline sold on an average rainy day in March and on an average sunny day in March in San Francisco, California.