A zombie statistic is a false or misleading statistic, often reanimated from studies conducted many years ago and now printed as truth without citation.
Well-constructed prevalence studies on health conditions require large populations to produce statistically relevant results. The rarer the disease, the bigger the required population. The expense and effort to accurately assess the prevalence of a rare disease is beyond the reach of most study budgets. As a result, zombie-like rare disease prevalence estimates may not have a basis in reality. In addition, publications rarely segment prevalence rates by U.S. health insurance market (commercial, Medicaid, Medicare, individual) even though sometimes significant differences in prevalence may exist among different covered populations. The United States incentivizes the development of drugs to treat rare diseases through the Orphan Drug Act of 1983, which defines a rare disease as having fewer than 200,000 individuals affected.
In this article, Milliman’s Donna Wix and David Williams used real-world data to calculate the age-adjusted prevalence rate for three diseases: rheumatoid arthritis, which is uncommon but not a rare disease by the Orphan Drug Act definition; ulcerative colitis, which could be considered a rare disease depending on which source is cited; and hemophilia, for which an antihemophilic factor was approved in 2010 by the U.S. Food and Drug Administration (FDA) under the 1983 Orphan Drug Act. They then compared these results to zombie statistics commonly cited.