unit 2 pt 1 - Definitions of Epidemiology Measures of...

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Measures of Morbidity and Mortality Part 1 Dr. H. Stockwell Definitions of Epidemiology ± The study of the distribution , determinants and deterrents of morbidity and mortality in human populations. (Oleckno) Numerator and denominator ± Numerators and denominators The Numerator: What is Health and Disease How do we define “health”? - WHO: physical, mental and social well-being Problems with definition of health from an epidemiologic /research perspective? - Must define health or lack thereof in quantifiable terms, usually measure disease (morbidity and mortality) How do you define a disease? Changes in Disease definitions ± Definitions change as more is learned about disease and better tests about disease and better tests developed to measure the disease Changing disease definitions source: Aschengrau and Seage The Denominator: Definition of a population ± What is a “population”? Group of people with a common characteristic(s) ± How can we define populations? Residence, catchment area, common event (disease etc) occupation etc (disease etc), occupation etc ± Why do we need to know? Determine who is at risk of disease
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Studying the Distribution of Disease The basic measures of epidemiology Counts - n Ratios - a/b one number divided by another Ratios one number divided by another (numerator and denominator are usually mutually exclusive) Proportions - a/a+b (no time period in the equation itself) – often expressed as a percent Rates - a/a+b per 1,000, 10,000, 100,000 over a specified period of time Counts: Most basic measure of disease frequency Count # in numerator: reflects the number of affected individuals in a population Count # in denominator: reflects the population at risk Numerator counts: useful for allocation of health resources Counts only of numerators: limited usefulness for epidemiologic purposes without knowing the size of the population at risk Ratios Ratio = A/B where A and B are usually mutually exclusive of one another ** There is no implied relationship between the numerator and denominator Ratios are typically used to compare the magnitude of two or more measures: - 60 students, 35 females, 25 males Ratio of female to male students = 35:25 = ( 35/25 =1.40) = 1.40:1 = 40% more females Proportions Everyone in numerator always included in the denominator ( a/a+b ) Tells what fraction of the population is affected Tells what fraction Always ranges from 0 to 1 (commonly expressed as percentage) Has no element of time within the calculation Proportions ± 60 students: ± 35 female, 25 male ± 30 students aged 25 years and over, 30 younger than 25 years What is the proportion of females? ± What is the proportion of females? ± What is the proportion of younger individuals (<25)? 35/60 = 58% 30/60 = 50% 30/60 =
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Top 10 causes of death as proportions of Dis. of heart Top 10 causes of death as proportions of all deaths, all ages, 2000 (NCHS/CDC faststats) Cancer Stroke Chronic lower respiratory disease Accidents 9% 6% 5% 4% 3% 3% 2% 2% Diabetes Pneumonia/influenza Alzheimer's Nephritis, etc Septicemia 37% 29% Rates Rates - a/a+b per 1,000, 10,000, or 100,000
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This note was uploaded on 07/15/2011 for the course PHC 6000 taught by Professor Staff during the Summer '08 term at University of South Florida.

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unit 2 pt 1 - Definitions of Epidemiology Measures of...

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