DA.reg {MethComp}R Documentation

Make a regresion of differeneces on averages

Description

For each pair of methods in data, a regression of the differences on the averages between methods is made and a linear relationship between methods with prediction standard deviations is derived.

Usage

  DA.reg(data,
    Transform = NULL,
    trans.tol = 1e-6)
  

Arguments

data A Meth object. May also be a data frame with columns meth, item and y.
Transform A character string, or a list of two functions, each other's inverse. The measurements are transformed by this before analysis. Possibilities are: "exp", "log", "logit", "pctlogit" (transforms percentages by the logit), "sqrt", "sq" (square), "cll" (complementary log-minus-log), "ll" (log-minus-log). For further details see choose.trans.
trans.tol The tolerance used to check whether the supplied transformation and its inverse combine to the identity. Only used if Transform is a list of two functions.

Details

If the input object contains replicate measurements these are taken as separate items in the order they appear in the dataset.

Value

A MethComp object, i.e. a list with three components, Conv, VarComp, and data. Conv is a three-dimensional array, with dimensions To, From (both with levels equal to the methods in data) and an unnamed dimension with levels "alpha", "beta", "sd.pred", "beta=1" and "s.d.=K". Conversting from method l to method k using

y_{k|l}=α+β y_l

with prediction standard deviation σ, just requires the entries [k,l,c("alpha","beta","sd.pred"]. The two last entries are p-values for the hypotheses: 1) β=1 and 2) standard errors are constant over the range. The latter is derived by regressiin the absoulte values of the residuals on the averages.
The VarComp element of the list is NULL, and only present for compatibility with the print method for MethComp objects.
The data element is the input datframe. The mesurements iny are left un-transformed.

Author(s)

Bendix Carstensen, Steno Diabetes Center, bxc$steno.dk

References

B Carstensen: Limits of agreement: How to use the regression of differences on averages. Technical Report 08.6, Department of Biostatistics, University of Copenhagen, http://www.pubhealth.ku.dk/bs/publikationer/Research_report_08-6.pdf, 2008.

Examples

data( milk )
DA.reg( milk )
data( sbp )
print( DA.reg( sbp ), digits=3 )

[Package MethComp version 0.7.1 Index]