Examining the Tools of Epidemiologists

Epidemiology in Healthcare

The National Center for Health Statistics (NCHS) and the National Immunization Program (NIP) track the number of deaths that occur due to measles within the United States (Gindler et al., 2004). Both programs are run by the Centers for Disease Control and Prevention (CDC); however, the data reporting systems for the two organizations are distinct. The NCHS reports deaths as either underlying-cause or multiple-cause mortality, but in the absence of measles confirmation by physical examination or laboratory results. By comparison, NIP reports de-identified information, but only confirmed cases. Gindler and colleagues (2004) compared the two reporting systems and the NIP system was found cable of reporting 71% of deaths due to measles, compared to 64% by NCHS. The death-to-case ratio (DCR) varied from 2.05 to 2.83 per 1,000 reported cases among the three databases during the 1989 outbreak. During this period, the prior annual average of 3,000 measles cases increased to 27,782 by 1990 and the DCR increased to over 2.0. In the aftermath of the outbreak there was a reinvigorated vaccination effort in the U.S. that helped to reduce the number of reported cases to 2,237 by 1992 and the DCR to zero by 1993. The highest DCR rates were for the very young and very old, as well as individuals with preexisting compromised immune systems. This information helps clinicians define which groups are most vulnerable to measles, so that they can target these groups with more aggressive vaccination programs.

The reported annual incidence of schizophrenia globally is only about 15.2 per 100,000 persons; however, the disease burden is comparatively high because it can persist for years or decades (Saha, Chant, Welham, & McGrath, 2005). Accordingly, estimates of the number of people who are currently suffering from schizophrenia are based on prevalence. Saha and colleagues (2005) performed a systematic review of the research literature and from this information defined the point, period, lifetime, and lifetime morbid prevalence risk as 4.6, 3.3, 4.0, and 7.2 per 1,000 persons, respectively. These statistics reveal that there is almost two orders of magnitude difference between the incidence and prevalence of schizophrenia globally. Assuming a global population of 7.15 billion (U.S. Census Bureau, 2014), the annual incidence of schizophrenia for 2014 would be about 1.1 million, but the annual prevalence would be about 23.6 million. This difference reveals the difference in information that can be provided by prevalence and incidence statistics. Prevalence estimates also reveal immigrants are almost twice as susceptible to developing schizophrenia when compared to residents. By comparison, researchers have shown that males tend to develop schizophrenia earlier than females (Rigby & Alexander, 2008) and this difference can best be revealed by examining the incidence of new diagnoses by age and gender.