11.55 “Mountain Biking May Reduce Fertility in Men, Study Says” was the headline of an article appearing in the San Luis Obispo Tribune (December 3, 2002). This conclusion was based on an Austrian study that compared sperm counts of avid mountain bikers (those who ride at least 12 hours per week) and nonbikers.

Ninety percent of the avid mountain bikers studied had low sperm counts, as compared to 26% of the nonbikers. Suppose that these percentages were based on independent samples of 100 avid mountain bikers and 100 nonbikers and that it is reasonable to view these samples as representative of Austrian avid mountain bikers and nonbikers.

a. Do these data provide convincing evidence that the proportion of Austrian avid mountain bikers with low sperm count is greater than this proportion for Austrian nonbikers?

b. Based on the outcome of the test in Part (a), is it reasonable to conclude that mountain biking 12 hours per week or more causes low sperm count? Explain.