Unit 4: Logical The study of disease transmission.


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Unit 4: Logical The study of disease transmission Unit 4 Learning Destinations: 1. Comprehend theory definition in epidemiologic studies. 2. Comprehend and ascertain measures of impact (danger distinction, hazard proportion, rate proportion, chances proportion) used to assess epidemiologic theories.
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Unit 4: Analytic Epidemiology

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Unit 4 Learning Objectives: 1. Comprehend speculation detailing in epidemiologic studies. 2. Comprehend and ascertain measures of impact (danger distinction, hazard proportion, rate proportion, chances proportion) used to assess epidemiologic theories. 3. Understand measurable parameters used to assess epidemiologic speculations and results: - P-values - Confidence interims - Type I and Type II slip - Power

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Unit 4 Learning Objectives (cont.): 4. Perceive the essential study outlines used to assess epidemiologic speculations: - Randomized trial - Prospective & review partner studies - Case-control study - Case-hybrid study - Cross-sectional study

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Assigned Readings: Textbook (Gordis): Chapter 11 Rothman: Random blunder and the part of measurements. In Epidemiology: an Introduction , Chapter 6, pages 113-129.

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Analytic Epidemiology Study of the DETERMINANTS of wellbeing related occasions

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Hypothesis Formulation Scientific Method (not one of a kind to epi) - Formulate a theory - Test the speculation

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Basic Strategy of Analytical Epi 1. Identify variables you are occupied with: • Exposure • Outcome 2. Define a theory 3. Compare the experience of two gatherings of subjects regarding the presentation and result

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Basic Strategy of Analytical Epi Note: Assembling the study gatherings to look at, whether on the premise of introduction or malady status, is a standout amongst the most critical components of study configuration. Preferably, we might want to realize what happened to uncovered people had they not been uncovered, but rather this is “counterfactual” since, by definition, such people were uncovered.

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Hypothesis Formulation The “Biostatistican’s” way H 0 : “Null” theory (expected) H 1 : “Alternative” speculation The “Epidemiologist’s” way Direct hazard gauge (e.g. best gauge of danger of ailment connected with the introduction).

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Hypothesis Formulation Biostatistican: H 0 : There is no relationship between the exposure and malady of interest H 1 : There is a relationship between the exposure and sickness of interest (beyond what may be normal from arbitrary lapse alone)

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Hypothesis Formulation Epidemiologist: What is the best gauge of the danger of ailment in the individuals who are presented contrasted with the individuals who are unexposed (i.e. uncovered are at XX times higher danger of ailment). This moves far from the basic dichotomy of yes or no for an introduction/ailment affiliation – to the evaluated greatness of impact independent of whether it varies from the invalid theory.

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Hypothesis Formulation “Association” Statistical reliance between two variables: • Exposure (danger component, defensive element, predictor variable, treatment) • Outcome (illness, occasion)

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Hypothesis Formulation “Association” The degree to which the rate of infection in persons with a particular presentation is either higher or lower than the rate of sickness among those without that introduction.

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Hypothesis Formulation Ways to Express Hypotheses: 1. Suggest conceivable events… The rate of tuberculosis will increase in the following decade .

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Hypothesis Formulation Ways to Express Hypotheses: 2. Suggest relationship between particular exposure and wellbeing related event… An elevated cholesterol admission is related with the improvement (danger) of coronary heart sickness.

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Hypothesis Formulation Ways to Express Hypotheses: 3. Suggest reason impact relationship…. Cigarette smoking is a reason for lung malignancy

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Hypothesis Formulation Ways to Express Hypotheses: 4. “One-sided” versus “Two-sided” One-sided case : Helicobacter pylori contamination is connected with expanded danger of stomach ulcer Two-sided illustration : Weight-lifting is connected with danger of lower back damage

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Hypothesis Formulation Guidelines for Developing Hypotheses: State the presentation to be measured as particularly as could be allowed. State the wellbeing result as particularly as could be expected under the circumstances. Endeavor to clarify the littlest sum of obliviousness

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Hypothesis Formulation Example Hypotheses: POOR Eating garbage sustenance is connected with the improvement of tumor. Great The human papilloma infection (HPV) subtype 16 is connected with the advancement of cervical growth.

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“Measures of Effect” Used to assess the exploration speculations Reflects the ailment experience of groups of persons with and without the exposure of interest Often alluded to as a “point estimate” (best appraisal of introduction/ailment relationship between the two gatherings)

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“Measures of Effect” • Risk Difference (RD) • Relative Risk (RR) - Risk Ratio (RR) - Rate Ratio (RR) • Odds Ratio (OR)

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“Measures of Effect” • Risk Difference (RD) The supreme contrast in the rate (danger) of malady between the uncovered gathering and the non-uncovered (“reference”) bunch

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“Risk Difference” Hypothesis: Asbestos presentation is connected with mesothelioma Results: Of 100 persons with high asbestos presentation , 14 create mesothelioma more than 10 years Of 200 persons with low/no asbestos presentation , 12 create mesothelioma more than 10 years

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“Risk Difference” Hypothesis: Asbestos introduction is connected with mesothelioma Results: Of 100 persons with high asbestos introduction , 14 create mesothelioma more than 10 years Of 200 persons with low/no asbestos presentation , 12 create mesothelioma more than 10 years

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“Risk Difference” Hypothesis: Asbestos presentation is connected with mesothelioma Results: Of 100 persons with high asbestos introduction , 14 develop mesothelioma more than 10 years Of 200 persons with low/no asbestos presentation , 12 develop mesothelioma more than 10 years RD = I E+ – I E-RD = (14/100) – (12/200) RD = 0.14 – 0.06 = 0.08 The total 10-year danger of mesothelioma is 8% higher in persons with asbestos presentation contrasted with persons with low or no presentation to asbestos.

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“Measures of Effect” • Risk Ratio • Rate Ratio Compares the frequency of malady (danger) among the uncovered with the occurrence of sickness (danger) among the non-uncovered (“reference”) by method for a proportion. The reference gathering expect an estimation of 1.0 (the “null” esteem) {“Relative Risk (RR)”}

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The ‘null’ esteem (1.0) CI uncovered = 0.0026 CI non-uncovered = 0.0026 CI uncovered = 0.49 CI non-uncovered = 0.49 IR uncovered = 0.062 for each 100K IR non-uncovered = 0.062 for every 100K RR = 1.0 RR = 1.0 RR = 1.0

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The ‘null’ esteem (1.0) • If the relative danger assessment is > 1.0, the introduction gives off an impression of being a danger factor for sickness. • If the relative danger assessment is < 1.0, the presentation gives off an impression of being defensive of infection event.

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“Risk Ratio” Hypothesis: Being liable to physical misuse in adolescence is associated with lifetime danger of endeavored suicide Results: Of 2,240 youngsters not subject to physical misuse , 16 have endeavored suicide. Of 840 kids subjected to physical misuse , 10 have endeavored suicide. Note that the line and section headings have been subjectively changed from the former illustration.

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“Risk Ratio” Hypothesis: Being liable to physical misuse in adolescence is connected with lifetime danger of endeavored suicide Results: Of 2,240 kids not subject to physical misuse , 16 have endeavored suicide. Of 840 youngsters subjected to physical misuse , 10 have endeavored suicide.

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“Risk Ratio” Hypothesis: Being liable to physical misuse in youth is associated with lifetime danger of endeavored suicide Results: Of 2,240 youngsters not subject to physical misuse , 16 have endeavored suicide. Of 840 kids subjected to physical misuse , 10 have endeavored suicide. RR = I E+/I E-RR = (10/840)/(16/2,240) RR = 0.0119/0.0071 = 1.68

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“Risk Ratio” RR = I E+/I E-= 1.68 Children with a background marked by physical misuse are approximately 1.7 times more prone to endeavor suicide in their lifetime contrasted with youngsters without a past filled with physical misuse. The danger of lifetime endeavored suicide is approximately 70% higher in kids with a history of physical misuse contrasted with youngsters without a background marked by physical misuse.

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“Rate Ratio” Hypothesis: Average every day fiber admission is related with danger of colon tumor Results: Of 112 grown-ups with high fiber consumption followed for 840 man yrs, 9 created colon malignancy. Of 130 grown-ups with moderate fiber consumption followed for 900 man yrs, 14 created colon disease Of 55 grown-ups with low fiber admission took after for 450 man yrs, 12 created colon malignancy.

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“Rate Ratio” • Assume that high fiber admission is the reference gath

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