STUDY GUIDECHLH 274EXAM 1Definition of epidemiology- The study of the distribution and determinants of disease frequency and health related events in populations and the application of this study to control health problemsDifferentiate between endemic, epidemic, and pandemic - Endemic- the habitual presence of a disease within a given geographic area- Epidemic- the occurrence in a community or region of cases of an illness clearly in excess of expectancy- Pandemic- an epidemic on a scale, during a pandemic large numbers of persons may be be affected and a disease may cross boardersMajor contributors to epidemiology- John Graunt- published natural and political observations made upon bills of mortality, British tradesman, developed procedures that allow epidemiologistto examine trends in birth and death vital stats- John Snow- chorea mapping used ecological analysis which is the comparisonof rates by region, cohort analysis, and case control analysis- James Lind- Scottish physician, conducted one of first randomized clinical trials in 1747, assigned men to various dietary treatments to determine the best way to prevent scurvy - William Farr- mid 1880’s, staticians consider him one of the major founders of modern epidemiology, devised a categorization system of death that laid the foundation for the international classification of disease- Doll & Hill- 1950’s, seminal studies showing unequivocal association betweensmoking and lung cancer, case control, studies signified shift from infectious to chronic disease in public health Definition of social epidemiology- The branch of epidemiology that studies the social distribution and social determinants of health," that is, "both specific features of, and pathways by which, societal conditions affect health- Social determinants- The social determinants of health refer to both specific features and pathways by which societal conditions affect health that potentially can be altered Hierarchy of epidemiologic study - Slides in notes from 8/28- Generate hypothesiso Case reportso Case serieso Ecological studieso Cross-sectional studieso Case control studieso Cohort studieso Randomized controlled trials- Establish causality Types of population/notes- Fixed and dynamic populationMathematical parameters- Used to relate number of cases of a disease, size of population, and time- Rate- time is an intrinsic part of the denominator, term is most misused o Example 36 miles/ 2 hours- Ratio- division of one number by anothero 36/2- Proportion- numerator is a subset of denominator often expressed as a percentage- an equation of two ratioso 36/2=18/1Measures of disease frequency- Incidence- quantifies number of onset cases of disease that develop in a population at risk during a specified time period. Useful to help in research on the etiology of diseaseo # of new cases/# of person at risk for developingo ex: we have 160 in our class and 5 people had a disease then 5 more get it in class- 10/160-5 - Prevalence- number of existing cases of disease in a population at a point in time, uses are describing the scope of a health problem in a population, estimating the frequency of an exposure, and determining allocation of heath resources o Number of existing cases of disease/ # of people in population at a pt in timeo Example 7000 people has arthritis in a city on Jan 1st in a population of70,000 so its 7000/70,000 = 10% or .1 o Point prevalence and period prevalence- Cumulative incidence- estimates the probability or risk that a person will develop disease during a specified time – another way to say it is it measures the disease frequency during a period of timeo # of new cases/ total populationo Example 1000 live births and 10 cases of SIDS so 10/1000= 1% in a year (all live births are at risk so they make up total pop)o Assumes that you have followed the entire population for the entire follow up periodo That makes it a bad choice for dynamic population - Incidence rate/density- this measure is a true rate because it directly integrates time into the denominatoro Number of new cases per population over a given period of timeo Consider the following example. Say you are looking at a sample population of 225 people, and want to determine the incidence rate of developing HIV over a 10-year period. At the beginning of the study (t=0) you find 25 cases of existing HIV. You follow-up at 5 years (t=5 yrs) and find 20 new cases of HIV. You again follow-up at the end of the study (t=10 yrs)and find 30 new cases. If you were to measure prevalence you would simply take the total number of cases (25 + 20 +30 = 75) and divide by your sample population (225). So prevalence would be 75/225 = 0.33 or 33%.Relationship between incidence and prevalence- Analogy- the water flowing down the waterfall symbolized incidence and water collecting in the pool at the base symbolizes prevalence- P=ID –the prevalence (P) of a disease is proportional to the incidence rate (I) times the duration (D) of a disease - If the duration of the disease is short and incidence in high, prevalence becomes similar to incidence- Short duration- cases recover rapidly or are fatal- If the duration of disease is long and incidence is low, prevalence increases greatly relative to low incidence Descriptive epidemiology - Examining the patterns of disease in a population and observing the basic features of its distribution in terms of person, place, and time- Primary focus: describing patterns of disease- Objectives to evaluate and compare trends in health and disease in order to provide basis for planning, provision, and evaluation of health service- Use measure of disease frequency- incidence/prevalence- Other measures related to morbidity and mortality-- Use rates- Need numerator, denominator, and time frameMeasures of comparison- Relative risk- tells you how many times higher or lower the disease risk is among the exposed as compared to the unexposed. o Measures the strength of association b/w an exposure and an outcome in cohort studieso Risk of exposed individuals compare to unexposedo (a/a+b)/ (c/c+d) o in cohort studies can use a 2x2 box to compareo when you find the RR it means individuals who have exposure are x% more likely to have the disease than unexposedo risk of 1= no association, <1 is negative association, >1 positive associationo start with exposure in cohort studies to see if you develop the disease or outcome - Odds ratio- for case control studies and can make a 2x2 boxo