EPI 824 Reproductive outcomes. Wilfried Karmaus Department of Epidemiology, MSU firstname.lastname@example.org You find class material in: http://www.msu.edu/course/epi/824/. Content. Scales Incidence, point / period / lifetime prevalence Sources of information Methods of determination
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Department of Epidemiology, MSU
You find class material in:
Science to describe distribution of health and its risk factors in a population
Natural and social science
Statistical models that describe different distribution
(time of unprotected intercourse)
We compare two or more proxy-measurements or two or more determination of the gold standard.
result of the test statistical models
Assessment of validity of a measurement
positive predictive value=a/(a+b)
negative predictive value = d/(c+d)
Pr(classified diseasedtruly diseased)
= a/(a + c)
truly non diseased)
= d/(b + d)
Validity of a measurement statistical models
criteria: - specificity and - sensitivity
Sensitive tests: high detection rate of persons
truly diseased (or truly exposed)
Specific tests: high detection rate of persons free of disease (or free of exposure)
Sensitivity and specificity of a test are independent of the prevalence of the disease (exposure).
OBSERVATION A statistical models
Reproducibility of a measurement = Reliability
Comparing measurements, not with a gold standard.
Reproducibility of a measurement statistical models
·Discrete variables: kappa coefficient ·Continuous variables: intra-class correlation coefficient (ICC)
perfect agreement: kappa = 1
chance agreement: kappa = 0