help for fagani

Fagan's bayesian nomogram

fagan #prev #lrp #lrn [, options]

where

#prev is the prior or pretest probability of disease

#lrp is the likelihood ratio of a positive test result

#lrn the likelihood ratio of a negative test result

Description

fagani creates a plot showing the relationship between the prior probability, the LR (combination of sensitivity and specificity), and the posterior probability.

Remarks

It is an immediate command, see help immed.

When Bayes theorem is expressed in terms of log-odds, the posterior log-odds are a linear function of the prior log-odds and the log likelihood ratio.

fagan plots an axis on the left with the prior log-odds, an axis in the middle representing the log likelihood ratio and an axis on the right representing the posterior log-odds.

Lines are drawn from the prior probability on the left through the LRs in the center and extended to the respective posterior probability on the right.

Options

legendopts(#) specify options that affect the plot legend.

ysize() and xsize() specify the height and width of plot respectively.

Example

. fagani 0.5 14.4 0.25

. fagani 0.25 20 0.05, ysize(8) xsize(6)

. fagani 0.45 6.4 0.25, scheme(s2mono)

Author

Ben Adarkwa Dwamena, Division of Nuclear Medicine, Department of Radiology, University of Michigan Medical School, Ann Arbor, Michigan.