Dear Alyson.

There is no general rule about this; however, my suggestion would be to use log-scaled values. This is because on a log-scale proportional changes in the trait are equal, independent of the magnitude of the trait. That is, a change of 1% in mass of whale is the same as a change in 1% in mass of a mouse. If your analysis includes both mice and whales, then on the original scale mice may appear to be changing very little in mass, while whales change a great deal - even if (relative to their sizes) both groups are changing just as much. On the other hand, if your analysis is of only whales or only mice it will make relatively little difference whether you use log-scaled data or the original values.

I hope this is of some help. All the best, Liam

Liam J. Revell, Associate Professor of Biology
University of Massachusetts Boston

On 7/13/2018 2:07 PM, Alyson Brokaw wrote:
Hello Everyone,

I am working with a comparative dataset using bat morphometrics. As part of
my analysis, I want to estimate the phylogenetic signal of my variables. I
understand how to do this using R. My question is more specifically about
what kind of data I should be using when calculating the estimates.

For the purposes of my other analyses (linear regressions), I have
log-transformed my data to meet assumptions for normality. When estimating
phylogenetic signal, should I use my non-transformed, raw variables or the
transformed variables? I get slightly different outputs if I run both on
the same measure. My intuition is that using the raw values is more
interpretable, but figured I would ask some people with more experience.

Thank you for your time.


Alyson Brokaw
M.S. Candidate: Biology, Humboldt State University
Cornell University '11, Ecology and Evolutionary Biology

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