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78 Cards in this Set
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define sensitivity

# of true positives divided by all people with disease


define specificity

# of true negatives divided by all people without disease


positive predictive value

# of true positives divided by all people who tested positive


negative predictive value

# of true negatives divided by all people who tested negative


what characteristic is desirable for a confirmatory test?

high specificity


what characteristic is desirable for a screening test

high sensitivity


define odds ratio

estimate of relative risk because don't have incidence data (casecontrol)


define relative risk

incidence of disease in person exposed to risk factor / incidence of disease in person not exposed to risk factor


what type of studies use odds ratio?

casecontrol studies


what type of studies use relative risk?

cohort studies


how are samples chosen for a casecontrol study

chosen based on presence (cases) or absence (controls) of disease


what type of information is being collected in a casecontrol study?

risk factors


how are samples chosen in a cohort study?

presence or absence of risk factors


what effect does a metaanalysis have on limitations or bias in studies?

can't overcome limitations


what does a metaanalysis try to achieve?

greater statistical power


what type of information is being collected in a cohort study?

development of disease


define clinical study

compares therapeutic benefits of 2 or more treatments or treatment/placebo


bias: subjects permitted to choose whether to go into drug group or placebo group rather than being assigned randomly

selection bias


knowledge or presence of disorder alters remembering by subjects (i.e. parents of kids w/ birth defects)

recall bias


subjects who volunteer to be in a study are not representative of population being studied

sampling bias


information gathered at an inappropriate time

latelook bias


name 4 ways to reduce bias

blind studies, placebo responses (having control group), crossover studies, randomization


define crossover study

each subjects acts as own control (patient receives drug then later on receives placebo, and vice versa)


define prevalence

total cases in population at given time/total population


define incidence

new cases in population over a given time / total population at risk during time


is prevalence or incidence greater for chronic disease?

prevalence


is incidence or prevalence greater for acute disease?

incidence


what is the relationship between prevalence and incidence (mathematically)?

prevalence = incidence x disease duration


what factor do you need to account for in calculating incidence?

people previously positive for disease are no longer considered at risk


how do you mathematically calculate the false negative rate?

1sensitivity


how do you mathematically calculate the false positive rate?

1specificity


when does the odds ratio approximate the relative risk?

when the prevalence of the disease is not too high


define precision

how reliable is the estimate (are all values closer together?)


define accuracy

how close is the estimate to the true mean


what is the difference between random error and systematic error?

random error: reduced precision in test; systematic error: reduced accuracy in test


what is the relationship between mean, median, and mode in a gaussian distribution?

all are equal


what is a bimodal statistical distribution?

2 modal peaks  two distinct populations


what is the relationship between mean, median and mode in a positive skew

mean>median>mode


where is the tail of a positive skew?

to the right


what is the relationship between mean, median, and mode in a negative skew?

mean<median<mode


where is the tail in a negative skew?

on the left


define null hypothesis

hypothesis of no difference


define alternative hypothesis

hypothesis that there is a difference


define type 1 error

stating there is a difference where no exists


what greek letter defines type I error?

alpha


define p value

probability of making type 1 error (say there's a difference when there isn't)


define type II error

stating there is no difference where one exists


what greek letter defines type II error?

beta


what is the mathematical equation for power?

1beta


define power

probaiblity of rejecting null hypothesis when it is indeed false


how do you increase the power?

increase sample size


what 3 factors does power depend on?

total number of end points experienced by population, difference in compliance between treatment groups, size of expected effect


how many people are within 1 standard deviation

68%


how many people are within 2 standard deviations

95%


how many people are within 3 standard deviation?

99.7%


what does SEM stand for?

standard error of the mean


what is the mathematical equation for standard error of the mean?

standard deviation/square root (sample size)


what is greater, standard error of the mean or standard deviation?

standard deviation


what is the relationship between sample size and standard error of the mean

SEM decreases as n increases


definition: range of values in which a specified probability of the mean of repeated samples would be expected to fall

confidence interval


if the 95% CI for a mean difference includes 0, what does this signify?

no significant difference, null hypothesis not rejected


if the 95% CI for an odds ratio or RR includes 1, what does this signify?

null hypothesis is not rejected


evaluate presence of statistically significant differences between 2 groups

Ttest


test that evaluates the presence of statistically significant differences between 3 or more groups

ANOVA (analysis of variance)


analyze categorial data or compare proportions

chi squared


what is the mathematical expression for coefficient of determination

r(squared)


between what 2 integers is r always located?

1 and 1


what does the absolute value of "r" indicate?

strength of correlatoin between 2 variables


what is already known when calculating sensitivity?

person has disease


what is already known when calculating specificity?

person doesn't have disease


what is already known when calculating PPV

preson already tested positive


what is already known when calculating NPV

person already tested negative


what factors does prevalence have a relationship with?

positive predictive value, negative predictive value


what is the relationship with prevalence and PPV

higher the prevalence, higher the PPV


what is the relationship between prevalence and NPV

lower the prevalence, higher the NPV


how do you calculate confidence interval

mean of sample plus/minus (Z score * SEM). 95% CI (z=2). 99.7% CI (z=3)


what is the relationship between accuracy, precision, and the width of the CI

wider the CI, the less precise, the more accurate (wider CI more likely to contain mean)


how to calculate an odds ratio

(person with risk factor that has "disease" x person without risk factor that does not have "disease) / multiple two opposites
