DTComPair (version 1.2.6)

ellipse.pv.rpv: Elliptical joint confidence region for relative positive and negative predictive value

Description

Returns a 100(1-alpha)% elliptical joint confidence region for the parameter vector {log(relative positive predictive value), log(relative negative predictive value)}.

Usage

ellipse.pv.rpv(x, alpha = 0.05, npoints = 100, exponentiate = FALSE)

Value

A list containing:

centre

the centre of the ellipse.

ellipse

an npoints x 2 matrix with the x and y coordinates for the ellipsoidal outline. Suitable for plot-ing.

Arguments

x

an object returned by the pv.rpv function.

alpha

significance level alpha used to compute the 100(1-alpha)% region. The default is 0.05, for a 95% region.

npoints

the number of points used in the ellipse. Default is 100.

exponentiate

a logical value indicating whether or not to exponentiate the values for the centre of the ellipse and for the the ellipsoidal outline. Defaults to FALSE.

References

Moskowitz, C.S., and Pepe, M.S. (2006). Comparing the predictive values of diagnostic tests: sample size and analysis for paired study designs. Clin Trials, 3(3):272-9.

See Also

pv.rpv and ellipse::ellipse.

Examples

data(Paired1) # Hypothetical study data
ftable(Paired1)
paired.layout <- tab.paired(d=d, y1=y1, y2=y2, data=Paired1)
paired.layout 
rpv.results <- pv.rpv(paired.layout)
ellipse.data <- ellipse.pv.rpv(rpv.results)
if(interactive()){
  plot(ellipse.data$ellipse, type = "l", ylim = c(-0.4, 0.2), xlim = c(-0.2, 0.2))
  points(ellipse.data$centre[1], ellipse.data$centre[2], col = "red", pch = 19)
  abline(h = 0, v = 0, lty = 3)
}