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Hiv Prevention PowerPoint Presentation

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Description : Hiv prevention public health

Tags : Hiv,terminology,Breast cancer,cancer

Published on : Jul 09, 2021 | Views : 1286 | Downloads : 0

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Measures of effect or association Dr Sumaya Mall Division of Epidemiology and Biostatistics School of Public Health University of the Witwatersrand Sumaya.mall@wits.ac.za
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Note on terminology Sometimes in the epidemiological literature, you might see the term ‘measures of association’ I prefer ‘measures of effect interested in knowing not only whether a link between a given exposure (e.g. smoking) and a certain outcome (e.g. myocardial infarction) is statistically significant, but also the magnitude of this relationship.
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Aims of today’s lecture Recap of the past two days Define and discuss measures of effect both relative and absolute Discuss specific measures of effect in relation to specific study designs Run through examples and calculations – use the example of breast disease
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Revision/Recap of the last two days
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How do we know statistically…? HIV infection is through sexual transmission? Smoking is related to cardiovascular disease? Childhood trauma is related to the onset of schizophrenia ?
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Relationships between exposures and disease HIV infection is through sexual transmission? Smoking is related to cardiovascular disease? Childhood trauma is related to the onset of schizophrenia ?
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Key to the field of epidemiology is…. Comparison !!!!! We always compare exposed and unexposed
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Measures of association/measures of effect Exposed people can have different levels and durations of exposure The total amount of a factor that reaches an individual is called the “dose.” We can then compare occurrences to calculate the risk that a health effect will result from an exposure. the measures describe the strength of an association between exposure and outcome.
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Breast cancer
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Breast cancer Breast cancer is a common cancer and leading cause of mortality Breast cancer incidence is increasing in low and middle income countries Recent literature suggests that there are some modifable risk factors for breast cancer
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Breast cancer
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Khalis et al (2020)
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Li et al (2020) Benign breast disease may lead to breast cancer and also to distress and reduced quality of life Common benign breast disease manifests as fibroadenoma or nodule of fibrous tissue often common in younger women Li et al aimed to explore if fibroadenoma is associated with risk factors common with breast cancer
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Li et al (2020)
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Li et al (2020)
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Calculations
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Cohort Study
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Let us calculate a risk ratio Also known as relative risk Risk in exposed/risk in unexposed Incidence in the exposed is a/a+b Incidence in the unexposed is c/c+d RR is incidence in exposed/incidence in unexposed
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Risk difference Instead of comparing two measures of disease frequency by calculating their ratio, one can compare them in terms of their absolute difference. The risk difference is calculated by subtracting the cumulative incidence in the unexposed group (or least exposed group) from the cumulative incidence in the group with the exposure. where (CIe) = cumulative incidence among the exposed subjects, and (CIu) is the cumulative incidence among unexposed subjects.
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Let us calculate an Odds Ratio In a case control study we do not know the incidence of disease SO we cannot calculate the RR OR is odds that an exposed person develops disease/odds that a non-exposed person develops disease (a/b)/(c/d)
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Let us calculate an Odds Ratio
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Let us calculate an Odds Ratio
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