biostats (i dont understand any of this just memorize random equations and pray) Flashcards
as prevalance decreases sensitivity and specificity what
remain unchanged
as prevelance decreases, NPV ____ and PPV ___
NPV increases
PPV decreases
PPV and prevealance are inversely related
sensitivity equation
A/ A+C
specificity equation
D/ B+D
positive predictive value equation
A / A +B
negative predicvitve value equation
D / D +C
lowering a tests upper limit for being a positive screen does what
increases FP
decreases FN
lower sPecificity, lower PPV
higher seNsitivity, higher NPV
raising the upper limit for being a postivie screen does what
increases the FN
decreases the FP
increases sPecificity
increases PPV
decreases seNsititivy
decreases NPV
high _____ test used for screening in disesae with low prevalance
sensitivity
increased prevalence does what to specificity and sensitivity
nothing
same with decreased prevelance
relative risk is used in what studies
cohort
equation relative risk
a/a+b / c/c+d
relative risk reduction equation
1 -RR
if prevelance is low then OR
= RR
berkson bias
study pop selected from hosptial is less healthy than general pop
healthy worker effect
study pop is healthier than the gen pop
non response bias
participating subjects differ from nonrespondents in meaningful ways
3 types of selection bias
berkson, healthy worker, non response
one survery teams hemoglobin machine malfunctioned and was not checked. so everyones Hb was the same when taken
measurement bias
subjects in different groups are not reateed the same
procedure bias
if observer expects treatment group to show signs of recovery, then he is more likely to document positive outcomes
obserrver expectancy bias
early detection makes it seem as though survival has increased, but natural hisotry of disease has not changed
lead time bias
positive skew
mean > median > mode
negative skew
mean < median < mode
