Important Formulas Flashcards
How to calculate percent likelihood when “either” or “or” is used?
Add the percents -> additive rule
How to calculate percent likelihood when “all” or “and” is used?
Multiply the percents -> multiplicative rule
How to calculate if tests are in normal range?
(.95) ^ # of normal tests predicated * 100
How to calculate how many standard deviations is a value from the mean?
- Find the mean
- Figure out how many standard deviations the provided numbers are
- Calculate!
How to calculate standard error of mean (SEM)?
SEM = standard deviation/ squareroot(number in sample)
What is the traditional alpha value?
.05
How to calculate standard deviation?
Square root of variance
How to calculate sensitivity?
TP/TP + FN
How to calculate specificity?
TN/TN + FP
How to calculate PPV (positive predictive value)?
TP/ FP+TP
How to calculate NPV (negative predictive value)?
TN/ FN+TN
Increasing raise cutoff will cause…
Sensitivity and NPV to decrease
Specificity and PPV to increase
Decreasing raise cutoff will cause…
Specificity and PPV to decrease
Sensitivity and NPV to increase
If we increase incidence + prevalence…
PPV will increase, NPV will decrease
Sensitivity + specificity do not change
If we decrease incidence + prevalence…
PPV will decrease, NPV will increase
Relative risk
Incidence of disease in exposed group/incidence of disease in unexposed group
If RR = 1.0…
No association
If RR > 1.0…
Positive association
If RR < 1.0…
Negative association
How to calculate absolute risk
of cases in risk group/total in risk group
Odds ratio
Odds of exposure among those with disease/odds of exposure among those without disease
If OR > 1.0
Risk factor is more likely!
If OR < 1.0
Risk factor is less likely
How to calculate attributable risk?
Absolute risk of exposure - absolute risk without exposure
How to determine number needed to harm?
1/attributable risk
How to calculate number needed to treat?
1/incidence
