Both baldness and heart attacks are more common in males than in females. Is there a link between the two? The answer to this question takes on importance when treatments for baldness are considered. Minoxidyl, a treatment for baldness, is effective in some cases of male pattern baldness when applied topically. If the underlying condition of baldness elevates the risk of cardiovascular diseases, then any increase in the risk of cardiovascular disease in Minoxidyl users might mistakenly be attributed to the drug and not to the underlying condition of baldness. A study by Lesko and co-workers (1993) addressed this question by looking at data for 722 controls and 665 cases. Subjects were under 55 years of age who were admitted to hospitals in Massachusetts and Rhode Island. (Staff from the School of Public Health at the Boston University School of Medicine telephoned the hospitals to locate eligible cases.) Cases were men admitted for and survived a first heart attack with no prior serious heart problems. Controls were men admitted to the hospitals for non-fatal, non-cardiac problems. Control subjects with a prior history of heart disease were excluded from the study. Cases and controls were interviewed, and the degree of male pattern baldness was determined on a scale of 1 (no baldness) to 5 (extreme baldness). Data are shown below.
Assignment. Read this study abstract. Data based on self-reported baldness status are shown here:
| Patient's Assessment | ||
|---|---|---|
| Baldness | Cases | Controls |
| 1 (no baldness) | 251 | 331 |
| 2 (mild baldness) | 165 | 221 |
| 3 (moderate baldness) | 195 | 185 |
| 4 (severe baldness) | 50 | 34 |
| 5 (extreme baldness) | 2 | 1 |
| Total | 663 | 772 |
Use these data to describe the association between baldness and heart attacks. Report the relevant conditional distributions (column percents). Advanced students should report odds ratios associated with each level of baldness and conduct a test of statistical significance. Discuss the role that lurking variables might play in explain the observed relationship.
Sources:
Lesko, S. M., Rosenberg, L., & Shapiro, S.. (1993). A case-control study of baldness in relation to myocardial infarction in men. JAMA, 269, (8): 998-1003. [full text]
Electronic Encyclopedia of Statistical Examples and Exercises (EESEE) story "Baldness and Heart Attacks" in Moore, D. S. (2004). The Basic Practice of Statistics (Third ed.). New York: W. H. Freeman.