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Unformatted text preview: Epidemiology 6000 Unit 2 Help Session 20 January 2011 7:309 pm Unit 2 Unit 2 Outline: Descriptive Epidemiology Basic Measures of Epidemiology Counts Ratios Proportions Rate Prevalence Point Prevalence # existing cases at a point in time # at risk at that point in time Period Prevalence (# existing cases at beginning of time period + new cases over time period) # in population (or in study, e.g. who you started with) Incidence Cumulative Incidence (CI) = # new cases / population at risk All people must complete the entire followup period. Incidence Density (ID) = # new cases / personyears at risk Used when all participants do not complete follow up because they die, dropout, etc. Crude and Adjusted Rates Crude rate = # of cases or deaths / total population Direct Adjustment  Adjusted/standardized rates needed because you cannot compare two populations that have different distributions of underlying characteristics that are associated with the disease. Review questions Who should be included in the denominator of incidence measures (cumulative incidence or incidence density)? Review questions Who should be included in the denominator of incidence measures (cumulative incidence or incidence density)? Answer: Only those people in the defined population who are at risk for developing the disease. Prevalent cases of the disease are not included because a prevalent case is not at risk of getting the disease. Review questions How are proportions and rates related? Review questions How are proportions and rates related? Answer: A rate is a proportion with a measure of time in the denominator. A rate measures the speed at which an event is happening. Unit 2 Practice Questions & Answers 1. In which of the following measures is the numerator not included in the denominator? a. Proportion b. Ratio c. Rate d. Incidence Unit 2 Practice Questions & Answers 1. In which of the following measures is the numerator not included in the denominator? a. Proportion b. Ratio c. Rate d. Incidence Unit 2 Practice Questions & Answers 2. Which of the following measures includes the element of time? a. Proportion b. Ratio c. Rate d. Cumulative incidence Unit 2 Practice Questions & Answers 2. Which of the following measures includes the element of time? a. Proportion b. Ratio c. Rate d. Cumulative incidence Unit 2 Practice Questions & Answers 3. Compare and contrast cumulative incidence and incidence density. Unit 2 Practice Questions & Answers 3. Compare and contrast cumulative incidence and incidence density. Cumulative incidence: a proportion population at risk of developing the disease as the denominator all participants in the study must complete the entire followup period Incidence density: a rate persontime for the denominator You can still calculate incidence density if people drop out of the study before the end of the followup period. the end of the followup period....
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 Summer '08
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 Demography, Miami

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