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45 Cards in this Set
- Front
- Back
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Main features of case control study?
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Compares diseased with non-diseased patients; looking for difference in exposures
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Main features of cohort?
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Compares exposed with non-exposed; looking for difference in outcomes
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What does prevalence measure?
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Probability that a person in a defined population has a disease at a point (or period) in time.
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What measure do you use to estimate burden of disease?
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Prevalence
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What defines an "at risk" individual?
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Do not have disease at start of follow up period AND are capable of developing disease
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What does cumulative incidence tell you?
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Probability that an individual in a given population will develop the disease over a specified time period
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What measure do you use to estimate disease risk?
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Cumulative incidence
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What is major difference between cumulative incidence and incidence rate?
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Cumulative incidence does not reflect effect of differing lengths of follow-up between individuals in study
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What does incidence rate measure?
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Average rate at which a disease develops in a population over a specified time period
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What measurement has units and what are they?
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Incidence rate; "per unit time"
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What type of study can study a number of outcomes from a single exposure?
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Cohort
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What types of bias do you have to be concerned about in a cohort study?
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Bias in measuring outcome
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What is incidence in exposed group?
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A / (A+B)
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What is incidence in unexposed group?
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C / (C+D)
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What is relative risk?
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A / (A+B)
------------- C / (C+D) |
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How is relative risk rate different from relative risk?
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Uses person-years (instead of persons) in the denominator
(this allows it to take into account loss to follow-up) |
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What is attributable risk? Formula?
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Measure of the absolute risk of exposure; difference between incidence in exposed and unexposed groups
(Incidence in Exposed) - (Incidence in Unexposed) |
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What is "number needed to treat"? Formula?
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Simple measure of absolute benefit resulting from treatment
Reciprocal of attributable risk 1/(attributable risk) |
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What is attributable risk?
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[A/(A+B)] - [C/(C+D)]
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What measurement do you use for a case control study?
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Odds Ratio
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What is a major source of bias in case-control studies?
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Recall bias
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What can you NOT measure in a case-control study?
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Incidence
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When would you NOT use a case-control study?
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Studying rare exposures
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What is odds ratio?
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(AD)/(BC)
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What type of study selects subjects based on presence or absence of disease?
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Case control
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What are the three concerns when thinking of internal validity?
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Bias, confounding, chance
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What is symbol for false positive rate?
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alpha
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What is symbol for false negative rate?
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beta
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What is type I error?
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False positives
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What is a type II error?
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False negatives
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What does the p value estimate?
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False positive rate (type I or alpha error)
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What does the study power estimate?
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False negative rate (type II or beta error)
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What does a p value of .05 mean?
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If the null hypothesis were true, there is a 5% chance of observing the study result or one more extreme
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What does width of confidence interval reflect?
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Sample size
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What is the formula for power?
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1 - beta
(beta is probability of making a type II error) |
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Differential recall is an example of what kind of bias?
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Information bias
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What is sensitivity?
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A/(A+C)
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What is specificity?
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D/(B+D)
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What is PPV?
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A/(A+B)
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What is NPV?
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D/(C+D)
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What does sensitivity of a diagnostic test tell you?
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Probability of a positive test if you have the disease
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What does the specificity of a diagnostic test tell you?
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Probability of a negative test if you do not have the disease.
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Which measures of a diagnostic test are intrinsic?
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Sensitivity and specificity
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As disease prevalence in population increases, what statistics regarding a diagnostic test change?
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PPV increases
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If you have a 100% specific diagnostic test, what does that mean?
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You have NO false positives
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