Revision 00658171adb5faee19d3c7cc4a08f98e0ec99110 authored by Mark Stevenson on 08 April 2013, 00:00:00 UTC, committed by Gabor Csardi on 08 April 2013, 00:00:00 UTC
1 parent 56f396c
epi.nomogram.Rd
\name{epi.nomogram}
\alias{epi.nomogram}
\title{Post-test probability of disease given sensitivity and specificity of a test}
\description{
Computes the post-test probability of disease given sensitivity and specificity of a test.
}
\usage{
epi.nomogram(se, sp, lr, pre.pos, verbose = FALSE)
}
\arguments{
\item{se}{test sensitivity (0 - 1).}
\item{sp}{test specificity (0 - 1).}
\item{lr}{a vector of length 2 listing the positive and negative likelihood ratio (respectively) of the test. Ignored if \code{se} and \code{sp} are not null.}
\item{pre.pos}{the pre-test probability of the outcome.}
\item{verbose}{logical, indicating whether detailed or summary results are to be returned.}
}
\value{
A list containing the following:
\item{lr}{the likelihood ratio of a positive and negative test.}
\item{prob}{the post-test probability of the outcome given a positive and negative test.}
}
\references{
Hunink M, Glasziou P (2001). Decision Making in Health and Medicine - Integrating Evidence and Values. Cambridge University Press, pp. 128 - 156.
}
\examples{
## EXAMPLE 1
## You are presented with a dog with lethargy, exercise intolerance,
## weight gain and bilaterally symmetric truncal alopecia. You are
## suspicious of hypothyroidism and take a blood sample to measure
## basal serum thyroxine (T4).
## You believe that around 5\% of dogs presented to your clinic with
## a signalment of general debility have hypothyroidism. The serum T4
## has a sensitivity of 0.89 and specificity of 0.85 for diagnosing
## hypothyroidism in the dog. The laboratory reports a serum T4
## concentration of 22.0 nmol/L (reference range 19.0 to 58.0 nmol/L).
## What is the post-test probability that this dog is hypothyroid?
epi.nomogram(se = 0.89, sp = 0.85, lr = NA, pre.pos = 0.05, verbose = FALSE)
## The post-test probability that this dog is hypothyroid is 24\%.
## EXAMPLE 2
## A dog is presented to you with severe pruritis. You suspect sarcoptic
## mange and decide to take a skin scraping (LR+ 9000; LR- 0.1). The scrape
## returns a negative result (no mites are seen). What is the post-test
## probability that your patient has sarcoptic mange? You recall that you
## diagnose around 3 cases of sarcoptic mange per year in a clinic that
## sees approximately 2 -- 3 dogs per week presented with pruritic skin disease.
pre.pos <- 3 / (3 * 52)
epi.nomogram(se = NA, sp = NA, lr = c(9000, 0.1), pre.pos = pre.pos,
verbose = FALSE)
## If the skin scraping is negative the post-test probability that this dog
## has sarcoptic mange is 0.2\%.
}
\keyword{univar}% at least one, from doc/KEYWORDS
\keyword{univar}% __ONLY ONE__ keyword per line
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