asht (version 1.0.1)

Vpo: Variance for estimated Mann-Whitney parameter under proportional odds.

Description

A function to calculate the variance of the estimated Mann-Whitney parameter under the proportional odds model.

Usage

Vpo(PHI, tf, ny, nx)

Value

the variance of the estimated Mann-Whitney parameter

Arguments

PHI

Mann-Whitney parameter

tf

tie factor

ny

sample size for the y variable

nx

sample size for the x variable

Details

Uses uniroot to find the variance numerically. The approximation using the LAPH method (Lehmann alternative model combined with the proportional hazards model) is much faster and is the default.

Examples

Vpo(.7,.8,5,7)
## Compare to LAPH method
VLAPH<- function(PHI,tf=tiefactor,ny=n.y,nx=n.x){
        tf*(PHI*(1-PHI)/(ny*nx))*
          (1+((ny+nx-2)/2)*
             ((1-PHI)/(2-PHI)+PHI/(1+PHI)))
      }   
VLAPH(.7,.8,5,7)