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78 Cards in this Set
- Front
- Back
define sensitivity
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# of true positives divided by all people with disease
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define specificity
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# of true negatives divided by all people without disease
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positive predictive value
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# of true positives divided by all people who tested positive
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negative predictive value
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# of true negatives divided by all people who tested negative
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what characteristic is desirable for a confirmatory test?
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high specificity
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what characteristic is desirable for a screening test
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high sensitivity
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define odds ratio
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estimate of relative risk because don't have incidence data (case-control)
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define relative risk
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incidence of disease in person exposed to risk factor / incidence of disease in person not exposed to risk factor
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what type of studies use odds ratio?
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case-control studies
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what type of studies use relative risk?
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cohort studies
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how are samples chosen for a case-control study
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chosen based on presence (cases) or absence (controls) of disease
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what type of information is being collected in a case-control study?
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risk factors
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how are samples chosen in a cohort study?
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presence or absence of risk factors
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what effect does a meta-analysis have on limitations or bias in studies?
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can't overcome limitations
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what does a meta-analysis try to achieve?
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greater statistical power
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what type of information is being collected in a cohort study?
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development of disease
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define clinical study
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compares therapeutic benefits of 2 or more treatments or treatment/placebo
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bias: subjects permitted to choose whether to go into drug group or placebo group rather than being assigned randomly
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selection bias
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knowledge or presence of disorder alters remembering by subjects (i.e. parents of kids w/ birth defects)
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recall bias
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subjects who volunteer to be in a study are not representative of population being studied
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sampling bias
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information gathered at an inappropriate time
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late-look bias
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name 4 ways to reduce bias
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blind studies, placebo responses (having control group), crossover studies, randomization
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define crossover study
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each subjects acts as own control (patient receives drug then later on receives placebo, and vice versa)
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define prevalence
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total cases in population at given time/total population
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define incidence
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new cases in population over a given time / total population at risk during time
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is prevalence or incidence greater for chronic disease?
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prevalence
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is incidence or prevalence greater for acute disease?
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incidence
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what is the relationship between prevalence and incidence (mathematically)?
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prevalence = incidence x disease duration
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what factor do you need to account for in calculating incidence?
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people previously positive for disease are no longer considered at risk
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how do you mathematically calculate the false negative rate?
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1-sensitivity
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how do you mathematically calculate the false positive rate?
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1-specificity
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when does the odds ratio approximate the relative risk?
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when the prevalence of the disease is not too high
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define precision
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how reliable is the estimate (are all values closer together?)
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define accuracy
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how close is the estimate to the true mean
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what is the difference between random error and systematic error?
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random error: reduced precision in test; systematic error: reduced accuracy in test
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what is the relationship between mean, median, and mode in a gaussian distribution?
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all are equal
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what is a bimodal statistical distribution?
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2 modal peaks - two distinct populations
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what is the relationship between mean, median and mode in a positive skew
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mean>median>mode
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where is the tail of a positive skew?
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to the right
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what is the relationship between mean, median, and mode in a negative skew?
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mean<median<mode
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where is the tail in a negative skew?
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on the left
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define null hypothesis
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hypothesis of no difference
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define alternative hypothesis
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hypothesis that there is a difference
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define type 1 error
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stating there is a difference where no exists
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what greek letter defines type I error?
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alpha
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define p value
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probability of making type 1 error (say there's a difference when there isn't)
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define type II error
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stating there is no difference where one exists
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what greek letter defines type II error?
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beta
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what is the mathematical equation for power?
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1-beta
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define power
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probaiblity of rejecting null hypothesis when it is indeed false
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how do you increase the power?
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increase sample size
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what 3 factors does power depend on?
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total number of end points experienced by population, difference in compliance between treatment groups, size of expected effect
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how many people are within 1 standard deviation
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68%
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how many people are within 2 standard deviations
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95%
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how many people are within 3 standard deviation?
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99.7%
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what does SEM stand for?
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standard error of the mean
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what is the mathematical equation for standard error of the mean?
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standard deviation/square root (sample size)
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what is greater, standard error of the mean or standard deviation?
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standard deviation
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what is the relationship between sample size and standard error of the mean
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SEM decreases as n increases
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definition: range of values in which a specified probability of the mean of repeated samples would be expected to fall
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confidence interval
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if the 95% CI for a mean difference includes 0, what does this signify?
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no significant difference, null hypothesis not rejected
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if the 95% CI for an odds ratio or RR includes 1, what does this signify?
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null hypothesis is not rejected
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evaluate presence of statistically significant differences between 2 groups
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T-test
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test that evaluates the presence of statistically significant differences between 3 or more groups
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ANOVA (analysis of variance)
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analyze categorial data or compare proportions
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chi squared
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what is the mathematical expression for coefficient of determination
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r(squared)
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between what 2 integers is r always located?
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-1 and 1
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what does the absolute value of "r" indicate?
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strength of correlatoin between 2 variables
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what is already known when calculating sensitivity?
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person has disease
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what is already known when calculating specificity?
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person doesn't have disease
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what is already known when calculating PPV
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preson already tested positive
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what is already known when calculating NPV
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person already tested negative
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what factors does prevalence have a relationship with?
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positive predictive value, negative predictive value
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what is the relationship with prevalence and PPV
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higher the prevalence, higher the PPV
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what is the relationship between prevalence and NPV
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lower the prevalence, higher the NPV
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how do you calculate confidence interval
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mean of sample plus/minus (Z score * SEM). 95% CI (z=2). 99.7% CI (z=3)
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what is the relationship between accuracy, precision, and the width of the CI
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wider the CI, the less precise, the more accurate (wider CI more likely to contain mean)
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how to calculate an odds ratio
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(person with risk factor that has "disease" x person without risk factor that does not have "disease) / multiple two opposites
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