# Statistics Flashcards

1
Q

Likelihood ratio (negative)

A
```False negative (1 - sensitivity)
Divided by
True negative (specificity)```
2
Q

Likelihood ratio (positive)

A
```True positive (sensitivity)
Divided by
False positive (1 - specificity)```
3
Q

Positive predictive value (PPV)

A

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)

4
Q

Pre-test probability

A

Prevalence of the disease

All disease positive
Divided by
Total

5
Q

Sensitivity

A

‘True positive rate’

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

6
Q

Specificity

A

‘True negative rate’

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

7
Q

Probability (risk)

A

Probability of event
Divided by
Total at risk

8
Q

Publication bias

A

Unpublished negative trials exaggerate true effect size

Greatest threat to validity

9
Q

Odds ratio (OR)

A

Probability of event
Divided by
Probability of no event

Case control/cross sectional studies

10
Q

Hazard ratio (HR)

A

RR averaged over time (duration of study)

Survival analysis

11
Q

Number needed to treat

A

1
Divided by
Absolute risk reduction

12
Q

Absolute risk reduction

A

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

13
Q

Relative risk reduction

A

1 - RR

Expressed as a percentage

14
Q

Relative risk

A

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

Expressed as decimal
RCT or cohort study