Equations

Question 1

Sensitivity?

Answer 1

= TP / (TP + FN)

Question 2

Specificity?

Answer 2

= TN / (TN + FP)

Question 3

Positive predictive value?

Answer 3

= TP / (TP + FP)

Question 4

Negative predictive value?

Answer 4

= TN / (TN + FN)

Question 5

Odds ratio (for case control studies)?

Answer 5

= (a/c) / (b/d) = ad / bc

Question 6

Relative risk?

Answer 6

= a/(a + b) / c/(c + d)

Question 7

Attributable risk?

Answer 7

= (a/a + b) - (c/c + d)

Question 8

Number needed to treat?

Answer 8

1/absolute risk reduction

Question 9

Number needed to harm?

Answer 9

1/attributable risk

Question 10

BMI?

Answer 10

= weight in kg/(height in meters)^2

Question 11

Incidence rate?

Answer 11

of NEW cases in a specified time period / population at risk during same time period

Question 12

Prevalence?

Answer 12

of EXISTING cases / population at risk

Question 13

Alternative to calculating prevalence?

Answer 13

Incidence rate x avg dz duration

Question 14

1 - FN?

Answer 14

Sensitivity

Question 15

1 - FP?

Answer 15

Specificity

Question 16

What tests have high FPs and low threshold?

Answer 16

Screening tests

Question 17

What tests have high FNs and high threshold?

Answer 17

Confirmatory tests

Question 18

How do you increase PPV and decrease NPV?

Answer 18

Increasing prevalence and pretest probability

Question 19

Moving the curve to the right?

Answer 19

Increase specificity

Question 20

Moving the curve to the left?

Answer 20

Increase sensitivity

Question 21

Risk?

Answer 21

Exposed with disease / total # of exposed

Question 22

Probability (p)?

Answer 22

The probability of making a type I error (FP) or rejecting the null hypothesis when it is true

Question 23

Power?

Answer 23

(1 - B) = the probability of rejecting the H0 when it is false, or the probability of accepting the H1 when it is true

Question 24

CI = 95%, what is the Z-score

Answer 24

1.96 (2 SD)

Question 25

CI = 99%, what is the Z-score?

Answer 25

2.58 (3 SD)

Question 26

CI?

Answer 26

Mean +/- Z-score (SD / square root of sample size)