A study was done to compare the lung capacity of
coal miners to the lung capacity of farm workers. The
researcher studied 200 workers of each
type. Other factors that might affect lung capacity are smoking habits and exercise habits. The
smoking habits of the two worker types are similar, but the coal miners generally exercise less
than the farm workers.
1. Which of the following is the explanatory variable in this study?
b. Lung capacity
c. Smoking or not