Equations Flashcards
Sensitivity?
= TP / (TP + FN)
Specificity?
= TN / (TN + FP)
Positive predictive value?
= TP / (TP + FP)
Negative predictive value?
= TN / (TN + FN)
Odds ratio (for case control studies)?
= (a/c) / (b/d) = ad / bc
Relative risk?
= a/(a + b) / c/(c + d)
Attributable risk?
= (a/a + b) - (c/c + d)
Number needed to treat?
1/absolute risk reduction
Number needed to harm?
1/attributable risk
BMI?
= weight in kg/(height in meters)^2
Incidence rate?
of NEW cases in a specified time period / population at risk during same time period
Prevalence?
of EXISTING cases / population at risk
Alternative to calculating prevalence?
Incidence rate x avg dz duration
1 - FN?
Sensitivity
1 - FP?
Specificity
What tests have high FPs and low threshold?
Screening tests
What tests have high FNs and high threshold?
Confirmatory tests
How do you increase PPV and decrease NPV?
Increasing prevalence and pretest probability
Moving the curve to the right?
Increase specificity
Moving the curve to the left?
Increase sensitivity
Risk?
Exposed with disease / total # of exposed
Probability (p)?
The probability of making a type I error (FP) or rejecting the null hypothesis when it is true
Power?
(1 - B) = the probability of rejecting the H0 when it is false, or the probability of accepting the H1 when it is true
CI = 95%, what is the Z-score
1.96 (2 SD)
CI = 99%, what is the Z-score?
2.58 (3 SD)
CI?
Mean +/- Z-score (SD / square root of sample size)
