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32 Cards in this Set

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a study that is chosen based on presence or absence of disease and then information collected about risk factors
case-control study
a cohort study is what kind of study?
observational
in this type of study, the sample is chosen about presence or absence of risk factors and subjects are followed over time for development of disease
cohort study
define prevalence
total cases in population at a given time/ total population
define incidence
new cases in population over a given time period/total population at risk during that time

incidence is new incidents
for what type of diseases is prevalence greater than incidence?
chronic diseases
for what type of diseases does prevalence equal incidence?
acute diseases
for what type of test is high sensitivity desirable?
screening
define sensitivity and give formula
number of true positives divided by number of all people with the disease: a/a+c
how do you calculate the false negative rate?
1-sensitivity
for what type of test is high specificity desirable for?
confirmatory test
define specificity and give formula
number of true negatives divided by number of all people without the disease: d/b+d
1-specificity is equal to what?
false positive rate
what is positive predictive value and how do you calculate it?
probability of havinig a condition given a positive test - number of true positives divided by number of people who tested positive for the disease: a/a+b
what is negative predictive value and how do you calculate it?
probability of having a condition given a negative test - number of true negatives divided by number of people who tested negative for a disease: d/c+d
which are dependent on the prevalence of disease: sensitivity/specificity or predictive values?
predictive values
when prevalence is higher, what increases?
positive predictive value
when prevalence is lower what increases?
negative predictive value
what is an odds ratio?
odds of having disease in exposed group divided by odds of having disease in unexposed group (odds calculated within group as number with disease divided by number without disease)
what is the formula for odds ratio?
(a/b)/(c/d) = ad/bc
what is relative risk?
disease risk in exposed group dividd by disease risk in unexposed group - risk is calculated within a group as number with disease divided by total number of people in group
what is the formula for relative risk?
a/(a+b)/c/(c+d)
what is a type I error?
stating that there is an effect when none exists; equal to p
what is a type II error?
stating that there is not an effect of difference when one exists (power= 1-type II)
what does Z equal for the 95% confidence interval?
1.96
what is the formula for confidence interval?
CI=range from (mean-Z(SEM) to (mean+Z(SEM)
what does standard error of the mean equal?
standard deviation/square root of n
a t-test checks the difference between what?
the means of 2 groups
what does ANOVA check?
the difference between the means of 3 or more groups
what does chi square check?
difference between 2 or more percentages or proportions of categorical outcomes (not means)
mean > median > mode is what kind of skew?
positive - tail on right
mean < median < mode is what kind of skew?
negative - tail on left