# Statistics Flashcards

Likelihood ratio (negative)

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

Likelihood ratio (positive)

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

Positive predictive value (PPV)

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)

Pre-test probability

Prevalence of the disease

All disease positive

Divided by

Total

Sensitivity

‘True positive rate’

True positives

Divided by

Total with the disease (true positive + false negative)

Specificity

‘True negative rate’

True negatives

Divided by

Total without the disease (true negative + false positive)

Probability (risk)

Probability of event

Divided by

Total at risk

Publication bias

Unpublished negative trials exaggerate true effect size

Greatest threat to validity

Odds ratio (OR)

Probability of event

Divided by

Probability of no event

Case control/cross sectional studies

Hazard ratio (HR)

RR averaged over time (duration of study)

Survival analysis

Number needed to treat

1

Divided by

Absolute risk reduction

Absolute risk reduction

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

Minus

Risk of outcome on therapy

Relative risk reduction

1 - RR

Expressed as a percentage

Relative risk

Probability of outcome on therapy

Divided by

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

Expressed as decimal

RCT or cohort study