BA.est {MethComp}R Documentation

Bias and variance components for a Bland-Altman plot.

Description

A variance component model is fitted to method comparison data with replicate measurements in each method by item stratum. The purpose is to simplify the construction of a correct Bland-Altman-plot.

Usage

  BA.est( data, linked=TRUE, exch=!linked )
  

Arguments

data A data frame representing method comparison data with replicate measurements, i.e. with variables meth, item, repl and y.
linked Are the replicated linked within item across methods?
exch Are the replicated echangeable within (item,methods)? This is just for convenience.

Details

The model fitted is:

y=alpha_m + mu_i + c_mi + a_ir + e_ir, var(c_mi)=tau_m^2, var(a_ir)=nu^2, var(e_mir)=sigma_m^2

We can only fit separate variances for the tau's if more than two methods are compared (i.e. nM > 2).

NOTE: Currently, the author is too ignorant about the ins and outs of lme to find out how to get different tau's when nM>2. Therefor the estimates in this case are equal i.e. from the model postulated.

Value

A list with two elements:

bias Vector of estimates of alpha_m, the first element is always 0.
variances Vector of variance components, nM tau's, one nu if linked, and nM sigma's.

Author(s)

Bendix Carstensen

References

Carstensen, Simpson & Gurrin: Statistical models for assessing agreement in method comparison studies with replicate measurements, Preprent, Departmet of Biostatistics, University of Copenhagen, 2007, http://www.pubhealth.ku.dk/bs/publikationer/Research_report_07-14.pdf/.

See Also

BA.plot,tab.repl,perm.repl

Examples

data( ox )
BA.est( ox )
BA.est( ox, exch=TRUE )
data( sbp )
BA.est( sbp )
BA.est( sbp, exch=TRUE )

[Package MethComp version 0.1.12 Index]