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Unformatted text preview: Chapter 5
Principles of Epidemiology From the Greek word meaning “upon the people”, The study of epidemics. Initially it was used to study outbreaks such as cholera, plague, etc.. Today we use it to track many chronic diseases. The practice of epidemiology now includes the control and prevention of health problems. “Epidemiology is the study of the distribution and determinants of healthrelated states and events in specified populations and the application of this study to the control of health problems”
• Distribution= relationship between health problem and the population (place and time) Epidemiology Epidemiological Concepts Rates and Risks • Case – A particular instance of a disease or outcome of interest. • Risk – The probability or likelihood of an event occurring (that people will acquire a disease) • Risk factor – Clinically important signs associated with an increased likelihood of acquiring a disease. Epidemiological Concepts
• Incidence – How frequently a disease occurs in a population:
Identify a group of susceptible people who are initially free of the disease Examine them periodically over a period of time to find out how many new cases occur. • Prevalence – Fraction or proportion of a group possessing a disease or condition at a specific time. Observing (observations that heart disease was low in vegetarian diets) Counting cases or events (can use vital statistics) Relating cases or events to the population at risk – (CHD is number one cause of death in the US) Making comparisons (Seven Countries Study) (Let’s look at Figures 52, 53, 54, p.142 143) Developing hypotheses Testing the hypothesis (migration studies) Drawing scientific inferences Conducting experimental studies Epidemiologic Method Deaths per/100,000 in 1965 from all causes and CHD (black) Bias
• • • Possible Explanations for Possible Research Observations Research Chance Observation is incorrect because of random variation Truth Selection bias Measurement bias Confounding bias (presence of another variable that accounts for the observation) (unconscious changes in eating patterns) Types of Epidemiological Studies Ecological or correlational studies Crosssectional or prevalence studies • Compare the frequency of events in different populations with the per capita consumption of certain dietary factors (often use disappearance data) one group of people eat more/less of particular food • Examine the relationships among dietary intake, diseases, and other variables as they exist in a population at a particular time. (camera snap shot) • 24hour dietary recall Types of Epidemiological Studies Cohort or incidence studies • More like a moving picture of events occurring within populations. A group of people (cohort) free of the disease are identified and examined. They are then followed for many years and are examined periodically. Just came out – prostate cancer study • Example: Framingham Heart Study began in 1949. Casecontrol Study Controlled Trials Cohort Study • Type of observational analytical study; enrollment into the study is based on the presence (case) or absence (control) of disease. • Randomized trial conducted as a doubleblind experiment • Read Dietrelated Studies NIH p. 151. Nurses Health Study, Women’s Health Initiative ...
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- Spring '08