laracrystalo's version from 2016-07-17 21:29


Question Answer
PPV and prevalence association?PPV increases with increasing disease prevalence and decreases with decreasing disease prevalence
NPV and prevalence association?NPV decreases with increasing disease prevalence and increases with decreasing disease prevalence
type I erroralpha. rejecting the null hypothesis when it is actually true
type II errorbeta. accepting the null hypothesis when it is actually false
P < alphaideal, this is statistically significant and means rejecting the null
P > alphafail to reject the null hypothesis
R = 1perfect correlation
R = 0no correlation at all
R > 0+ correlation so positive slope
R < 0- correlation so negative slope
1 standard deviation68%
2 standard deviations95%
3 standard deviations99.7%
how does a larger sample size affect power?increases power
how does a larger sample size affect Confidence Interval?decreases confidence interval
precision is akin toreliability
accuracy is akin to validity
what factors make something reproducible?precision and reliability
what factors make something compared to the gold standardaccuracy and validity
standard error of meanSD / sq rt of sample size
confidence intervalmean +/- Z (SEM)
Z value?1.96 for 95% ; 2.58 for 99%
incidencenumber of new cases / number at risk
prevalence number of existing cases / total population
positive skewmode < median < mean (R skew)
negative skewmode > median > mean (L skew)
which study type looks at odds ratio?case control
what does case control find?odds ratio
what studies find relative risk?RCT or cohort
what do cohort studies find?relative risk
what do RCT studies find?relative risk
what do cross sectional studies find?disease prevalence
what studies find disease prevalence?cross sectional
snap-shot in timecross sectional
no controlscase series
when prevalence is low, what happens to OR and RR?they become more equal
how do you increase precision?decrease standard deviation and increase statistical power
most affected by outliers?mean
least affected by outliers?mode
primary disease preventionprevent (vaccination, condoms)
secondary disease preventionscreening (pap)
tertiary disease preventiontreatment (chemo)
phase I trialtoxicity, safety, pharm dynamics and kinetics
phase II trialefficacy, dosing, adverse effects
phase III trialcompare to standard
phase IV triallong term adverse effects
OR(a/c) / (b/d) OR ad/bc
RRa/a+b / c/c+d
ARa/a+b - c/c+d
ARRc/c+d - a/a+b
failure of precisionrandom error
failure of accuracysystematic error
reproducibility of test resultsprecision aka reliability
the test measures what it is supposed toaccuracy aka validity


Question Answer
study population selected form hospital is less healthy than general populationberkson bias (selection bias)
study population is healthier than general populationhealthy worker effect (selection bias)
participating subjects differ from nonrespondents in meaningful waysnon-response bias (selection bias)
awareness of disorder alters recall by subjectsrecall bias
common in retrospective studiesrecall bias
information is gathered in a way that distorts itmeasurement bias
subjects in different groups are not treated the sameprocedure bias
researchers belief in the efficacy of treatment changes the outcomepygmalion effect (observer-expectancy bias)
factor is related to both exposure and outcomeconfounding bias
early detection is confused with increased survivallead time bias
reduce selection bias?randomization
reduce recal bias?decrease time from exposure to follow up
reduce measurement bias?use standardized method of data collection
reduce procedure bias or pygmalion effect?blinding and placebos
reduce confounding bias?multiple repeated studies, crossover studies, matching
reduce lead time bias?measure back-end survival
change in behavior in a study group resulting from knowing they are being observedhawthorn effect
what does matching patients control for?confounding

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