Epidemiology Key Terms & Measures

1. EpidemiologyKey Terms & Measures Fran C. Wheeler, Ph.D School of Public Health University of South Carolina Columbia, SC 29208 (803) 777-5054 Fran.wheeler@sc.edu

2. Developed as part of an Enhanced AHEC Community Partnership for Health Professions Workforce and Educational Reform project funded by the Health Resource and Service Administration (HRSA)

3. OBJECTIVES • epidemiology and role as foundation for public health • common measures of disease frequency • strengths and weaknesses of study designs

4. Epidemiology • Study of distribution of determinants and antecedents of health and disease in human populations • Application of results to control of health problems

5. From Hippocratesto John Graunt • Fifth century BCE, Hippocrates pointed to the need to understand the environment and the risks it posed to understand the experience of disease • 1662, John Graunt analyzed weekly reports of births and deaths in London, quantifying patterns of disease in the population

6. From William Farrto John Snow • 200 years later, Dr. William Farr was made responsible for medical statistics in the Office of the Registrar General for England and Wales • A mere 20 years later, John Snow completed his study of cholera

7. Modern Experiences • Evaluation of risk factors for chronic diseases using case controls • Long term population studies using cohorts • Design of clinical trials to evaluate interventions

8. Expected level Endemic Sporadic Epidemic Pandemic Three Essential Components • Disease distribution • Disease determinants • Disease frequency

9. Epidemiologic Studies • Descriptive • Analytic

10. Descriptive Studies • Frequency of occurrence of particular condition • Patterns of occurrence according to person, place and time

11. Analytic Studies • Observational studies • case-control studies • cohort studies • prospective • retrospective • Experimental studies

12. Case Control Study Exposure Disease ? ? Key Basis for selection of group for study = present = absent

13. Prospective Cohort Study Exposure Disease ? ? Key Basis for selection of group for study = present = absent

14. Retrospective Cohort Study Exposure Disease ? ? Key Basis of selection of group for study = present = absent

15. Analytic Studies • Observational studies • Experimental studies • Intervention studies • Clinical trials

16. Basic Presentation of Results All rates and ratios discussed can be calculated from this

17. Smokingand Carcinoma of the Lung

18. Bias information selection Confounding extraneous factors Effect modification statistical interaction Interpreting Results: Measurement Errors

19. Strength of the association Consistency Temporality Plausibility Biological gradient Interpreting Results: Cause-Effect Relationship

20. Measures of Disease Frequency • Prevalence • Incidence

21. Prevalence= number of existing cases divided by total population Visual examination survey 310 X 100 = 12.5% 2477 Prevalence

22. Types of Prevalence Measures

23. Incidence • Incidence = number of new cases in a given period of time divided by the total population at risk • Bacteremia among contraceptive users • 27/483 X 100 = 5.6%

24. Types of Incidence Measures

25. Crude Category specific Age adjusted Rates Commonly Used in Epidemiology