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`Session 4.1 Basic Concepts of EpidemiologyBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006What is Epidemiology?3 Greek roots:Epi: Upon. Demos: Human population. Logia: Science. &quot;Science that deals with the distribution and. determinants of diseases in human populations&quot;.By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006RationaleDiseases do not occur by chance: there are always determinants for the disease to occur. Diseases are not distributed at random: Distribution is related to risks factors that might need to be studied.By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006The epidemiologic triangleAgent Disease Host EnvironmentBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006The epidemiologic TriangleRisk factorsCancerEnvironmentHostBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Risk factors Host CarcinogenesisEnvironmentBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Risk factors Host EnvironmentBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Risk factors Host CarcinogenesisCancerEnvironmentBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Risk factors Host CarcinogenesisCancer 1ry prevention 2ry prevention 3ry preventionEnvironmentBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Ratio, Proportion, and RateA sample with 2 categories, X and Y (e.g. males and females) X : Y = Ratio (Male : Female Ratio) X/(X+Y) % = Proportion A population P with Z events (cases) Z/P per 1,000 (constant) = RateBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Measures of RiskBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006PopulationExposed UnexposedRisk Factor Others÷Relative RiskOthersBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006PopulationExposed UnexposedRisk FactorAttributable RiskOthersBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006PopulationExposed UnexposedRisk Factor OthersAttributable Fraction %By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006The absolute riskSynonymous with incidence Means the rate of occurrence of the condition or disease. The basic rate from which relative and attributable risks are derivedBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Relative riskThe risk of one group with a factor (e.g. cigarette smokers) compared with the risk of a reference group without such a factor (e.g. Nonsmokers) The ratio of the incidence of the group with the factor to the incidence of the group without the factor. Factors associated with disease by virtue of elevated relative risks are termed risk factors .By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Attributable riskThe amount of the absolute risk (incidence) that can be attributable to one particular factor (e.g. smoking). It is computed by taking the incidence rate of the group with the factor (smokers) and subtracting the rate for the group without the factor (nonsmokers). The excess suffered by the smokers is the attributable risk due to smoking. Indicates the excess of disease due to a factor in that subgroup of the population that is exposed to the factor .By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006The relative risk does not measure the probability that someone with the factor will develop the disease . The individual with the factor might still have a very remote chance of getting the disease, if the disease is rare . Measures the strength of an association between a factor and a certain outcome; A high relative risk points toward causation and is useful in research for the etiology of disease .By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Measurements of riskRelative Risk = Incidence among exposed / Incidence among unexposed Attributable Risk = Incidence among exposed - Incidence among unexposed Attributable fraction % = Attributable risk / incidence among exposed. By analogy, measure could be calculated for Preventable fraction %.By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Clinical ImplicationsAlthough a factor may have a high relative risk, with reference to a common outcome or disease, if that factor is rare in the population, the impact on the population will be small. Patients with familial multiple polyposis have a relative risk of 20 for cancer of the large bowel Incidence of large bowel cancer due to familial multiple polyposis is very small because the attribute is rare it is necessary that a factor both have a high relative risk and be prevalent in the population in order for it to influence the incidence of the disease in the populationBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Association and CausationBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Types of AssociationAn association may be artifactual, noncausal, or causal. An artifactual or spurious association may arise because of bias in the study.. Noncausal associations occur in two ways. The disease may cause the exposure (rather than the exposure causing the disease). The disease and the exposure are both associated with a third (confounding) factor, X, known or unknown. In measuring exposure we are inadvertently measuring the effect of X.By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Causal and noncausal associationsCausal association Exposure Noncausal association (1) Disease (2) ×DiseaseExposureDisease ExposureBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Coffee, smoking and CHDCoffee consumption (cups per day) 0 1-5 6+CHD mortality in males aged 55-64 (deaths per 1,000 per year) 6 8 12By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Coffee, smoking and CHDCigarette consumption (pack. per day) 0 1-2 3+CHD mortality in males aged 55-64 (deaths per 1,000 per year) 4 10 15By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Coffee, smoking and CHDCoffee (cups per day) 0 1-5 6+ AllCigarettes (packs per day) 0 4 6 5 4 1-2 9 10 9 10 30 15 13 16 15All 6 8 12By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Coffee, smoking and CHDCigarette smoking(confounding factor)Coffee drinkingCHD mortalityBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Coffee, smoking and CHDCigarette smokingCHD mortalityBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 20065 criteria of causationconsistency of the association. strength of the association. specificity of the association. temporal relationship of the association. coherence of the association.By: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006Statistical association present Bias absent Apply 5 criteria satisfiedabsentConclude the suspected factor is not implicated in etiology Conclude association is artifactual Conclude association is noncausalpresentNot satisfiedConclude association is causalBy: AS Ibrahim and NNH Mikhail, Ankara Cancer Epidemiology Course, April 2006`

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Microsoft PowerPoint - Epi 4.1 Basic Concepts of Epidemiology
Microsoft PowerPoint - Epi 4.1 Basic Concepts of Epidemiology