The functions DA2y and y2DA are convenience functions that
convert the estimates of intercept, slope and sd from the regression of
\(D=y_1-y_2\) on \(A=(y_1+y_2)/2\), back and forth
to the resulting intercept, slope and sd in the relationship between
\(y_1\) and \(y_2\), cf. Carstensen (2010), equation 6.
Usage
DA2y(a = 0, b = 0, s = NA)
Value
DA2y returns a 2 by 3 matrix with rownames c("y1|2","y2|1")
and columnnames c("int","slope","sd"), calculated under the
assumption that the differences were formed as D <- y1 - y2.
Arguments
a
Intercept in the linear relation of the differences y1-y2 to
the averages (y1+y2)/2. If a vector of length>1, this is used instead
of a, b and s, and b and s are ignored.
b
Slope in the linear relstion of the differences to the averages.
s
SD from the regression of the differences in the averages. Can be
NA.
DA2y takes the intercept(a), slope(b) and sd(s) from
the relationship (y1-y2)=a+b((y1+y2)/2)+e with sd(e)=s,
and returns a two by 3 matrix with columns "int","slope","sd" and
rows "y1|2","y2|1".
References
B. Carstensen: Comparing methods of measurement: Extending the
LoA by regression. Stat Med, 29:401-410, 2010.