In a study that was highly publicized, doctors discovered that aspirin seems to help prevent heart attacks. The research project, which was scheduled to last for 5 years, involved 22,000 American physicians (all male). Half took an aspirin tablet three times per week, while the other half took a placebo on the same schedule.

The researchers tracked each of the volunteers and updated the records regularly. Among the physicians who took aspirin, 104 suffered a heart attack; 189 physicians who took the placebo had a heart attack.

Determine whether these results indicate that aspirin is effective in reducing the incidence of heart attacks.