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13 Cards in this Set
- Front
- Back
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Case control study
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Looks in the past
Do these ppl w/the disease have a Hx of this risk factor compared to another group w/out the disease? Calculate: Odds ratio OR = ad/bc |
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Cohort study
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Looks to the future
Has two groups of ppl, one w/risk factors and the other w/out, and see if they get the disease Calculate: Relative risk RR = a/(a+b) ________ c/(c+d) |
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Cross-sectional study
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Looks at data from a population and relative risk factors
Calculate: Prevalence Prev. = incidence X disease duration |
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Prevalence = ?
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total cases/total population
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Incidence = ?
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new cases in a period of time/ total population at risk
exclude ppl that already have the disease |
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Compare prevalence to incidence
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total cases/total population
Higher than incidence in chronic disease, same as incidence in acute disease |
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Phase I, II, III of clinical trial
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I: healthy volunteers, small group
II: diseased volunteers, small group III: large group of patients, randomly assigned treatment or placebo (better if double-blinded) |
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Sensitivity
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Rules OUT
TP / TP+FN or 1-false negative rate (high FN = not sensitive) |
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Specificity
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Rules IN
TN / TN + FP or 1-false positive rate (high FP = not specific) |
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Positive predictive value
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TP / TP + FP
high prevalence = high PPV |
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Negative predictive value
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TN / TN + FN
high prevalence = low NPV |
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Number needed to treat/harm
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1 / absolute risk increase
where absolute risk increase = event rate of treatment - event rate of placebo |
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attributable risk = ?
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a/a+b - c/c+d
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