Equations! Flashcards
Number needed to treat
NNT = 1/ARR (remember to round answer up to whole number)
Absolute risk reduction
ARR = CER-EER
Risk ratio
RR = EER/CER
Control event rate
CER = outcome in controls/total number of controls
Experimental event rate
EER = outcome in cases/total number of cases
Relative risk ratio
RRR = CER-EER/CER
Positive predictive value
PPV = true positive/all positives
Negative predictive value
NPV = true negative/all negatives
Sensitivity
True positive/true positive + false negative
Specificity
True negative/false positive + true negative
Positive likelihood ratio
LR+ = sensitivity/1-specificty
Negative likelihood ratio
LR- = 1-sensitivity/specifity
Interquartile range
IQR = median of upper 1/2 - median of lower 1/2
Standard error of the mean
SEM = standard deviation/Sq root of no. of patients
Odds ratio
OR = (a/c) / (b/d)
Prevalence = incidence x duration. True or False?
True
Standard deviation
Sq root of variance
Post test odds
LR X pretest odds
Pretest odds = prevalence
False positive rate
1-specificity
Population attributable risk
attributable risk x proportion of population exposed
CIs for NNT (upper CI)
1/lower limit ARR CI
CIs for NNT (lower CI)
1/higher limit for ARR CI
Post test probability
Posttest odds / (Posttest odds + 1)
Pretest odds
Pretest probability / (1 - Pretest probability)
