EPIDEMIOL_20091(6) day 8 and 9.ppt

Epidemiology/ Influences on health Faculty: Stephen Buka, ScD; Ilana Gareen, PhD; Annie Gjelsvik, PhD; Karl Kelsey, MD, Eric Loucks, PhD; Mark Lurie, PhD; Deborah Pearlman, PhD; Patricia Risica, PhD; Elizabeth Triche, PhD Epidemiology Study of the distribution and determinants of diseases and injuries in human populations Goal: Limit disease, injury, and death in a community by intervening to prevent or limit outbreaks or epidemics of disease and injury Goal accomplished by: Describing outbreaks and designing studies to analyze them Epidemiologists are concerned with numbers TB cases by age group TB cases and rates by age group, per 10,000 Rates Number of events in a given population over a given period or at a given point in time Allow a comparison of events that occur at different times, in different places, or in different populations Have greater meaning because they are based upon the population-at-risk Population-at-risk Members of a population who are susceptible to disease or death from a particular cause General categories of rates Natality (birth) Mortality or fatality (death) Morbidity (sickness) Types of morbidity rates Incidence Prevalence Incidence (per 10,000) Number of new cases of a health outcome in a population-at-risk in a given time period. TB cases # of cases Total # Population Age group January cases age group 45-54 3 11 6,736 55-64 1 8 4,534 Incidence rate (45-54) = 3/6,736 x 10,000 = 4.5 Prevalence (per 10,000) Total number of cases of a health outcome in a population-at-risk in a given time period. TB cases # of cases Total # Population Age group January cases age group 45-54 3 11 6,736 55-64 1 8 4,534 Prevalence rate (45-54) = 11/6,736 x 10,000 = 16.3 Denominator Multiplier What is the prevalence rate per 100? TB cases # of cases Total # Population Age group January cases age group 45-54 3 11 6,736 55-64 1 8 4,534 Prevalence rate (45-54) = 11/6,736 x 100 = .16 Denominator Multiplier What is the prevalence rate per 1000? TB cases # of cases Total # Population Age group January cases age group 45-54 3 11 6,736 55-64 1 8 4,534 Prevalence rate (45-54) = 11/6,736 x 1,000 = 1.6 Question Is there an association between eating cereal and vomiting among Brown students? and Types of Epidemiological Studies Descriptive: Person Place Time Types of Epidemiological Studies Descriptive: Ecological study: observe occurrences of a disease or condition within a population to determine if it is temporally associated with some phenomenon or exposure in the same population Results of Ecological Study Types of Epidemiological Studies Descriptive: Ecological study Case Report: profile of a single patient Types of Epidemiological Studies Descriptive: Ecological study Case Report Case series: describes characteristics of a number of patients with given health outcome Types of Epidemiological Studies Descriptive: Ecological study Case Report Case series Cross-sectional survey: assessment of status of individuals with respect to presence or absence of both exposure and health outcome at same time point Results from Cross-Sectional Survey Types of Epidemiological Studies Descriptive Analytic: testing the hypotheses formulated from descriptive studies Types of Epidemiological Studies Descriptive Analytic Case-control studies Case-Control Studies Identification of factors that are more common or pronounced in people with a health outcome compared to a comparison group without the health outcome Results presented as odds ratios Odds ratio is probability statement about association between particular health outcome and a specific risk factor. Results of Case-Control Study Vomiting Eat PUFFS cereal Yes No Total (Case) (Control) Yes 55 (a) 35 (b) 90 No 45 (c) 65 (d) 110 100 100 200 Odds ratio = Odds of exposure:non-exposure in cases Odds of exposure:non-exposure in controls OR = (a/c) / (b/d) = (55/45) / (35/65) = 1.22/0.54 = 2.3 Results of Case-Control Study Eat PUFFS cereal Vomiting Yes No Total (Case) (Control) Yes 55 (a) 45 (b) 100 No 35 (c) 65 (d) 100 90 110 200 Odds ratio = Odds of exposure:non-exposure in cases Odds of exposure:non-exposure in controls OR = (a/c) / (b/d) = (55/35) / (45/65) = 1.57/0.69 = 2.3 Results of Case-Control Study Vomiting Drink tea >1 time Yes No Total per day (Case) (Control) Yes 35 (a) 65 (b) 100 No 65 (c) 60 (d) 125 100 125 225 Odds ratio = Odds of exposure:non-exposure in cases Odds of exposure:non-exposure in controls OR = (a/c) / (b/d) = (35/65) / (65/60) = 0.53/1.08 = 0.49 Types of Epidemiological Studies Descriptive Analytic Case-control studies Cohort studies Cohort Studies Cohort--group of people who share some important characteristics Subjects classified on the basis of the presence or absence of exposure to a particular factor and then followed for a specified period of time to determine the development of health outcome in each exposure group Results presented as relative risk Results of Cohort Study Vomiting Eat PUFFS cereal Yes No Total Yes 10 (a) 100 (b) 110 No 7 (c) 148 (d) 155 17 248 265 Relative risk = Incidence rate among exposed Incidence rate among unexposed RR = a / (a+b) / c / (c+d) = (10/110) / (7/155) = .09/.05 = 1.8 Results of Cohort Study Stratification Freshman and Sophomores (N=157) Vomiting Eat PUFFS Yes No Total Yes 6 (a) 55 (b) 61 No 3 (c) 93 (d) 96 9 148 157 RR = Incidence rate among exposed Incidence rate among unexposed RR = a / (a+b) / c / (c+d) = (6/61) / (3/96) = .10/.03 = 3.3 Juniors and Seniors (N=108) Vomiting Eat PUFFS Yes No Total Yes 4 (a) 45 (b) 49 No 4 (c) 55 (d) 59 8 100 108 RR = Incidence rate among exposed Incidence rate among unexposed RR = a / (a+b) / c / (c+d) = (4/49) / (4/59) = .08/.07 = 1.1 Types of Epidemiological Studies Descriptive Analytic Intervention Intervention studies Exposure status of each participant is assigned by the investigator Strongest study because of the unique strength of randomization. Results of Randomized Intervention Vomiting Eat PUFFS cereal Yes No Total Yes 15 (a) 85 (b) 100 No 14 (c) 86 (d) 100 29 171 200 Relative risk = Incidence rate among exposed Incidence rate among unexposed RR = a / (a+b) / c / (c+d) = (15/100) / (14/100) = .15/.14 = 1.1