Elliptical joint confidence region for relative positive and negative predictive value

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)

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.

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.

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)
#>      y2   0   1
#> d y1           
#> 0 0     155  22
#>   1      53  31
#> 1 0      32  22
#>   1      78 319
paired.layout <- tab.paired(d=d, y1=y1, y2=y2, data=Paired1)
paired.layout 
#> Two binary diagnostic tests (paired design)
#> 
#> Test1: 'y1'
#> Test2: 'y2'
#> 
#> Diseased:
#>            Test1 pos. Test1 neg. Total
#> Test2 pos.        319         22   341
#> Test2 neg.         78         32   110
#> Total             397         54   451
#> 
#> Non-diseased:
#>            Test1 pos. Test1 neg. Total
#> Test2 pos.         31         22    53
#> Test2 neg.         53        155   208
#> Total              84        177   261
#> 
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)
}