Important Formulas

Question 1

How to calculate percent likelihood when “either” or “or” is used?

Answer 1

Add the percents -> additive rule

Question 2

How to calculate percent likelihood when “all” or “and” is used?

Answer 2

Multiply the percents -> multiplicative rule

Question 3

How to calculate if tests are in normal range?

Answer 3

(.95) ^ # of normal tests predicated * 100

Question 4

How to calculate how many standard deviations is a value from the mean?

Answer 4

1. Find the mean
2. Figure out how many standard deviations the provided numbers are
3. Calculate!

Question 5

How to calculate standard error of mean (SEM)?

Answer 5

SEM = standard deviation/ squareroot(number in sample)

Question 6

What is the traditional alpha value?

Answer 6

.05

Question 7

How to calculate standard deviation?

Answer 7

Square root of variance

Question 8

How to calculate sensitivity?

Answer 8

TP/TP + FN

Question 9

How to calculate specificity?

Answer 9

TN/TN + FP

Question 10

How to calculate PPV (positive predictive value)?

Answer 10

TP/ FP+TP

Question 11

How to calculate NPV (negative predictive value)?

Answer 11

TN/ FN+TN

Question 12

Increasing raise cutoff will cause…

Answer 12

Sensitivity and NPV to decrease
Specificity and PPV to increase

Question 13

Decreasing raise cutoff will cause…

Answer 13

Specificity and PPV to decrease
Sensitivity and NPV to increase

Question 14

If we increase incidence + prevalence…

Answer 14

PPV will increase, NPV will decrease
Sensitivity + specificity do not change

Question 15

If we decrease incidence + prevalence…

Answer 15

PPV will decrease, NPV will increase

Question 16

Relative risk

Answer 16

Incidence of disease in exposed group/incidence of disease in unexposed group

Question 17

If RR = 1.0…

Answer 17

No association

Question 18

If RR > 1.0…

Answer 18

Positive association

Question 19

If RR < 1.0…

Answer 19

Negative association

Question 20

How to calculate absolute risk

Answer 20

of cases in risk group/total in risk group

Question 21

Odds ratio

Answer 21

Odds of exposure among those with disease/odds of exposure among those without disease

Question 22

If OR > 1.0

Answer 22

Risk factor is more likely!

Question 23

If OR < 1.0

Answer 23

Risk factor is less likely

Question 24

How to calculate attributable risk?

Answer 24

Absolute risk of exposure - absolute risk without exposure

Question 25

How to determine number needed to harm?

Answer 25

1/attributable risk

Question 26

How to calculate number needed to treat?

Answer 26

1/incidence