Segars Epidemiology Flashcards
What is incidence?
new cases of a disease
” water from faucet filling a bathtub”
What is Prevalence?
old + new cases
“all the water in the bathtub”
calculate incidence
# new cases of illness divided by # people at risk of illness
always subtract out those not at risk (already have illness or are immune)
calculate prevalence (new + old cases)
total # cases divided by # people in population
calculate absolute risk reduction (ARR)
on test and see the word “absolute”, he wants us to subtract the placebo group% from the exposed/test group%
number of events (good or bad) in treated or control groups, divided by the number of people in that group
ie
group% - placebo group% = |x|
calculate relative risk reduction (RRR)
(ARR) / R placebo/unexposed
calculate number needed to treat (NNT)
1 / ARR in decimal format
ie 1/0.038 (38%) = 27 patients
Calculate Risk Ratio
risk of outcome (exposed)/ risk of outcome (nonexposed)
if ratio number is >1.0 then the event/outcome is what?
test answer should ay something like larger, biggger or more likely to occur in the comparison group
if ratio is <1.0 then the event/outcome is what?
test answer should say something like less, lower, smaller, tinier
interpreting ratios.
ie if RR = 1.53
study group has an increased 53% increased risk
if RR = 8.2
study group is 8 time more likely to occur
anything larger than 2 we start saying blah blah blah times more likely
if hazard ratio HR = 0.73
comparator numerator group has a 27% decreased chance of hazardous outcome
When interpreting Ratios (RR/OR/HR) look for….
1- group comparison orientation (blah vs blah)
2-direction of words (increased, decreased)
3-magnitude 80% (1.8)/ 20% (0.8)
our class will be numerator. other classes denominator
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When looking for confidence interval (CI) both values are on the SAME SIDE of 1.0, it is always statistically……..
significant
