| DA.reg {MethComp} | R Documentation |
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.
DA.reg(data,
Transform = NULL,
trans.tol = 1e-6)
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. |
If the input object contains replicate measurements these are taken as separate items in the order they appear in the dataset.
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.
Bendix Carstensen, Steno Diabetes Center, bxc$steno.dk
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.
data( milk ) DA.reg( milk ) data( sbp ) print( DA.reg( sbp ), digits=3 )