Dear morphometricians,
many thanks to all those who either in emails directly to me or to
morphmet contributed to this discussion.
It was very interesting and instructive.
I have a lot of sympathy for Ian's point about what to do when one uses
an ANCOVA to test slopes and finds that it is
These complicated issues aside, there is a simpler reason not to use a
residual from a regression as the basis for further analyses. If two
characters are under natural selection based on some combination -- such as
selection on a ratio between them -- then the current value of character Y
is a
Just as a quick follow up (and clarifications).
I recognize that there are already a number of methods to deal with these
well known issues (McCoy et al. 2006, Klingenberg 1996, Burnaby 1966,
etc..) and they may be better ways still. However, since the "using
residuals from a pooled
Dean and Andrea,
I wanted to follow up on what Dean wrote regarding using residuals from a
pooled within-group regression, and what I think may be important
discussion that follows from it. Considerable research has gone into
investigating this issue, and as Dean points out, most of the time it
Hi Andrea,
It is generally preferable to perform the more complex analysis with size
included as a covariate. Using a sequential approach that first obtains the
shape residuals and then examines patterns using these as data is not
guaranteed to get to the same, or even the correct, place.
