[R] Checking for orthogonal contrasts

[S Ellison]

A common point made in discussion of contrasts, type I, II, III SS etc
is that for sensible comparisons one should use contrasts that are 
'orthogonal in the row-basis of the model matrix' (to quote from
http://finzi.psych.upenn.edu/R/Rhelp02/archive/111550.html)

Question: How would one check, in R, that this is so for a particular
fitted linear model object?

Steve Ellison



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