chapter 3 biostats Flashcards
(34 cards)
1, 2, 3 SD around the mean = percents?
68
95
99.7
sensitivity test?
true positive / people with disease
for screening
low false negative rate
specificity test?
true negatives / people w/o disease
for confirmation of disease
low false positive rate
tradeoff between sensitivity and specificity
changing the cutoff for screening
if higher: more FNs, fewer FPs (if higher, you miss more people)
if lower: fewer FPs, more FPs (if lower, you catch more people that are not sick)
PPV
probability of having disease given positive test
true positive / all people with positive test
higher prevelance = higher PPV
high sensitivity = low PPV, bc more FPs
NPV
probability of not having disease given negative test
true negatives / all negatives
lower prevalence = higher PPV
high sensitivity = high NPV, bc fewer FNs
attributable risk
cases attributable to one risk factor = the amount by which the incidence of a test will decrease if the RF is removed
incidence rate in population - incident rate in smokers = attributable risk due to smoking
relative risk
compares disease risk in those exposed to a certain factor with the disease risk in people who have not been exposed to the factor
in prospective or experimental studies (not retrospective) cannot be calculated otherwise
significant if NOT 1
- 5 x more likely to develop disease if exposed to factor in question
- 5x less likely to develop disease if exposed == protective factor
OR
estimates RR in retrospective studies (case control)
skewed distribution
meaning not normal distribution
positive skew: lots of high values, tail of the curve is on the right. mean>median>mode
neg skew: lots of low values, tail on left. mean
test reliability
=precision
=reproducibility and consistency of test
= random error reducers reliabilitly and precision
test validity
=accuracy
=trueness of measurement, does it measure what it claims to measure
=systematic error reduces validity and accuracy
define correlation coefficicent
what degree are two variables related
-1 to +1
more strong = absolute value away from 0
if positive = positive correlation
if negative = negative correlation
confidence interval
95% certainty that the mean is within this range
1sd - 68
2sd - 95
3sd - 99.7
experimental studies prospective retrospective case series prevalence surveys
order of relevance from best to lowest
experimental studies
well matched controls
sometimes ethical c/f is why we can’t do it
prospective studies
cohort or observation
dividing groups based on presence of RF and following to determine the outcome
can determine incidnece + RR
retrospective studies
choose population samples after the RF
only OR, no incdence + RR
less expensive, better for rare disease
case series study
describes presentation of disease, good for rare disease
prevalence survey
cross-sectional
prevalence of disease and risk factor
could suggest a cause of disease
incidence versus prevalence
incidence= #new cases of disease in a unit of time incidence = absolute risk of developing a condition
prevalence = total number of all cases at a point in time
what happens to incidence and prevalence if disease can be treated to the point where only people can be kept along longer w/o being cured, what happens?
incidence = nothing prevalence = goes up
short term diseases = incidence>prevalence
long term = prevalence>incidence
nominal = no numeric value (day of week)
ordinal = ranking
continuous data
nominal/ordinal data = use chi square
t-test/anova = continueous data
pvalue
if p<0.05, then less than 5% chance that the data were obtained by random error or chance
