EBM Tables and Equations Flashcards
Prevalence =
(total #sick)/(total population)
 how many people are sick
 a single time point
 Prevalence can be used to estimate the likelihood of a diagnosis before any “tests”
Cumulative incidence:
(new cases)/(total population at risk at study start)
 how many people are getting sick (NEW CASES)
 incidence is a rate, it happens over a time interval
Incidence equation in steady state:
prevalence / duration
Duration equation in steady state:
prevalence / incidence
Prevalence equation in steady state:
(incidence) X (average duration)
alpha =
 the probability you’ll make a false hit.
 Arbitrarily, p = 0.05
 false hit = type 1 error
 5% of the time, we’ll make an error
beta =
 probability you won’t find a difference when one actually exists (false miss)
 false miss = type 2 error
 probability of missing a reality
power =
1  beta
 power of study to pick up a study when it actually does exist
 Low power is a common reason for type II errors.
2 X 2 tables for hypothesis testing:
(alpha, beta, and power)
2 X 2 tables for hypothesis testing:
(type 1 and 2 errors)
2 X 2 tables for hypothesis testing:
(false hits and false misses)
95% CI equation:
95% CI = mean +/ 1.96(SEM)
 SEM = SD/ √n
Standard error of the mean (SEM) eqaution:
SEM = SD/ √n
 SD = standard deviation
 n = sample size
The three types of prevention:
 Primary: before exposure (PREVENT)
 Secondary: after exposure (SCREEN)
 Tertiary: after disease process occurs (TREAT)
Standard deviation:
+/ 3SD contains –% of observations
99.7%
Standard deviation:
+/ 1SD contains –% of observations
68%
Standard deviation:
+/ 2SD contains –% of observations
95%
The three types of variation:

Overall variation:
 measurement variation + biological variation

Measurement variation:
 instrument variation + observer variation

Biological variation:
 intraindividual and interindividual