posterior_probability: Posterior probability of disease given prevalence and...

In GWG: Calculation of probabilities for inadequate and excessive gestational weight gain

Description

Computes the posterior probability of disease given prevalence (prior probability) and positive or negative likelihood ratio of a test. Furthermore it is possible to give out the posterior odds.

Usage

posterior_probability(prevalence,lrpos=-1, lrneg=-1 ,posterior_odds=FALSE)

Arguments

prevalence	The prevalence of a disease (=prior_odds).
lrpos	The positive likelihood ratio (only displayed on the output window if a values >= 0 has been entered).
lrneg	The negative likelihood ratio (only displayed on the output window if a values >= 0 has been entered).
posterior_odds	If TRUE the posterior odds will be displayed on the output window. Default is FALSE.

Details

posterior\_odds\_of\_disease = {prior\_odds} * {pos\_likelihood\_ratio}

prior\_odds = \frac{prior\_probability}{1-prior\_probability}

posterior\_probability\_of\_disease = \frac{posterior\_odds}{1+posterior_odds}

Value

posterior_probability_pos	Probability of disease given test is positive
posterior_probability_neg	Probability of no disease given test is negative
posterior_odds_pos	Posterior odds of test positive
posterior_odds_neg	Posterior odds of test negative

References

Petrie A, Sabin C (2005). Medical statistics at a glance (2nd ed). Wiley-Blackwell. Oxford.

Examples

##Prevalence is 0.5 and the positive likelihood ratio is 3:
posterior_probability(0.5, lrpos=3)

#The probability of disease given test is positive is 0.75.


##Prevalence is 0.5 and the negative likelihood ratio is 0.5:
posterior_probability(0.5, lrneg=0.5, posterior_odds=TRUE)

#The probability of no disease is 0.66 given test is negative and the 
#corresponding posterior odds is 0.5.

GWG documentation built on May 2, 2019, 4:43 a.m.