Statistics

Question 1

Likelihood ratio (negative)

Answer 1

False negative (1 - sensitivity)
Divided by
True negative (specificity)

Question 2

Likelihood ratio (positive)

Answer 2

True positive (sensitivity)
Divided by
False positive (1 - specificity)

Question 3

Positive predictive value (PPV)

Answer 3

Likelihood that those that tested positive actually have the disease
Also called post-test probability

Disease positive tested positive
Divided by
Total tested positive (true + false positive)

Question 4

Pre-test probability

Answer 4

Prevalence of the disease

All disease positive
Divided by
Total

Question 5

Sensitivity

Answer 5

‘True positive rate’

True positives
Divided by
Total with the disease (true positive + false negative)

Question 6

Specificity

Answer 6

‘True negative rate’

True negatives
Divided by
Total without the disease (true negative + false positive)

Question 7

Probability (risk)

Answer 7

Probability of event
Divided by
Total at risk

Question 8

Publication bias

Answer 8

Unpublished negative trials exaggerate true effect size

Greatest threat to validity

Question 9

Odds ratio (OR)

Answer 9

Probability of event
Divided by
Probability of no event

Case control/cross sectional studies

Question 10

Hazard ratio (HR)

Answer 10

RR averaged over time (duration of study)

Survival analysis

Question 11

Number needed to treat

Answer 11

1
Divided by
Absolute risk reduction

Question 12

Absolute risk reduction

Answer 12

Risk of outcome not on therapy (placebo/alternative therapy)
Minus
Risk of outcome on therapy

Question 13

Relative risk reduction

Answer 13

1 - RR

Expressed as a percentage

Question 14

Relative risk

Answer 14

Probability of outcome on therapy
Divided by
Probability of outcome not on therapy (placebo/alternative therapy)

Expressed as decimal
RCT or cohort study