Stats/Ethics

Question 1

What variables to use mean for

Answer 1

• Interval (ordered, numerical, where zero means nothing)
• Ratio (ordered, numerical, where zero means something)

Question 2

What variables to use median for

Answer 2

• Ordinal (ordered, named categories)
• Non-normally distributed interval/ratio

Question 3

What variables to use mode for

Answer 3

• Nominal (named categories like gender)

Question 4

Normal distribution has what percentage with 1 SD vs 2 SD

Answer 4

68% with mean +/- 1 SD
95% with mean +/- 2 SD

Question 5

Calculation for standard error of mean

Answer 5

= Sample standard deviation / sq root of sample size

Question 6

Relative risk calculation

Answer 6

• Chance of getting disease with treatment relative to placebo
  (Treated with disease / all treated) / (Placebo with disease / all placebo)

Question 7

Odds ratio calculation

Answer 7

• Number of disease in treated / number of diseased in placebo

Question 8

Number needed to treat calculation

Answer 8

1 / risk difference

Question 9

Absolute risk reduction

Answer 9

Difference in risk between treatment and placebo
= (Diseased placebo / all placebo) / (Diseased treated / all treated)

Question 10

Sensitivity calculation

Answer 10

Given a patient with disease, what’s the chance the test will be positive

• True + / All with disease
• SnOUT - 100% sensitive rules OUT disease
• Good screening tests have high sensitivity
• Higher sensitivity means higher false positive

Question 11

Specificity calculation

Answer 11

Given a healthy patient, what’s the chance test will be negative

• True - / All healthy
• SpIN - 100% specific rules IN disease
• Higher specificity is higher false negative

Question 12

Positive predictive value calculation

Answer 12

True + / All + test

Question 13

Negative predictive value calculation

Answer 13

True - / All - test

Question 14

Likelihood ratio calculations

Answer 14

Chance of a positive (or negative) test result in patient with disease relative to patient without disease

LR + = (True pos / all disease) / (False positive / all healthy)

LR - = (False neg / all disease) / (True neg / all healthy)

Question 15

Receiver operating curve graph ideal test

Answer 15

Sensitivity on y axis
1 - specificity on x axis
Best test is in the top left corner

Question 16

Cohort study design

Answer 16

Follow exposed and non-exposed forward in time to see if they get bad outcome
- Good for rare exposures, can measure prevalence of a disease

Question 17

Case control study design

Answer 17

• Collect cases and controls and look back in time to see if they were exposed
• Good for rare diseases, can’t measure prevalence

Question 18

Which tests to use for means (with 2, before/after and more than 2)

Answer 18

• 2: Student T-tests
• Before/after: paired T tests
• More than 2: ANOVA

Question 19

Which tests to use for medians (with 2, before/after)

Answer 19

• 2: Mann-Whitney-U
• Before/after: Wilcoxon signed

Question 20

Which test to use for time to event

Answer 20

Kaplain Meier

Question 21

Which test to use for proportions

Answer 21

Chi square
- Fischer’s test for small group

Question 22

Which test to use to predict a number or yes/no

Answer 22

Linear regression