Lesson 3: Measures of Risk
Summary and References
Because many of the variables encountered in field epidemiology are nominal-scale variables, frequency measures are used quite commonly in epidemiology. Frequency measures include ratios, proportions, and rates. Ratios and proportions are useful for describing the characteristics of populations. Proportions and rates are used for quantifying morbidity and mortality. These measures allow epidemiologists to infer risk among different groups, detect groups at high risk, and develop hypotheses about causes — that is, why these groups might be at increased risk.
The two primary measures of morbidity are incidence and prevalence.
- Incidence rates reflect the occurrence of new disease in a population.
- Prevalencereflects the presence of disease in a population.
A variety of mortality rates describe deaths among specific groups, particularly by age or sex or by cause.
The hallmark of epidemiologic analysis is comparison, such as comparison of observed amount of disease in a population with the expected amount of disease. The comparisons can be quantified by using such measures of association as risk ratios, rate ratios, and odds ratios. These measures provide evidence regarding causal relationships between exposures and disease.
Measures of public health impact place the association between an exposure and a disease in a public health context. Two such measures are the attributable proportion and vaccine efficacy.
- Kleinman JC, Donahue RP, Harris MI, Finucane FF, Madans JH, Brock DB. Mortality among diabetics in a national sample. Am J Epidemiol 1988;128:389–401.
- Arias E, Anderson RN, Kung H-C, Murphy SL, Kochanek KD. Deaths: final data for 2001. National vital statistics reports; vol. 52 no. 3. Hyattsville, Maryland: National Center for Health Statistics, 2003; 9:30–3.
- Centers for Disease Control and Prevention. Reported tuberculosis in the United States, 2003. Atlanta, GA: U.S. Department of Health and Human Services, CDC, September 2004.
- Last JM. A dictionary of epidemiology, 4th ed. New York: Oxford U. Press; 2001.
- Hopkins RS, Jajosky RA, Hall PA, Adams DA, Connor FJ, Sharp P, et. al. Summary of notifiable diseases — United States, 2003. MMWR 2003;52(No 54):1–85.
- U.S. Census Bureau [Internet]. Washington, DC: [updated 11 Jul 2006; cited 2005 Oct 2]. Population Estimates. Available from: http://www.census.gov/popestExternal.
- Williams LM, Morrow B, Lansky A. Surveillance for selected maternal behaviors and experiences before, during, and after pregnancy: Pregnancy Risk Assessment Monitoring System (PRAMS). In: Surveillance Summaries, November 14, 2003. MMWR 2003;52(No. SS-11):1–14.
- Web-based Injury Statistics Query and Reporting System (WISQARS) [online database] Atlanta; National Center for Injury Prevention and Control. [cited 2006 Feb 1]. Available from: https://www.cdc.gov/injury/wisqars.
- Centers for Disease Control and Prevention. Health, United States, 2004. Hyattsville, MD.; 2004.
- Wise RP, Livengood JR, Berkelman RL, Goodman RA. Methodologic alternatives for measuring premature mortality. Am J Prev Med 1988;4:268–273.
- McLaughlin SI, Spradling P, Drociuk D, Ridzon R, Pozsik CJ, Onorato I. Extensive transmission of Mycobacterium tuberculosis among congregated, HIV-infected prison inmates in South Carolina, United States. Int J Tuberc Lung Dis 2003;7:665–72.
- Tugwell BD, Lee LE, Gillette H, Lorber EM, Hedberg K, Cieslak PR. Chickenpox outbreak in a highly vaccinated school population. Pediatrics 2004 Mar;113(3 Pt 1):455–9.
- Uyeki TM, Zane SB, Bodnar UR, Fielding KL, Buxton JA, Miller JM, et al. Large summertime Influenza A outbreak among tourists in Alaska and the Yukon Territory. Clin Infect Dis 2003;36:1095–1102.
- Doll R, Hill AB. Smoking and carcinoma of the lung. Br Med J 1950;1:739–48.