pairwise - interpretation of allometric trajectories

[Mihajlo Milic]

Dear geomorph community,

I am performing the comparison of allometric trajectories between two groups using the "pairwise" function. The results I obtained seem fine, however, I would appreciate some help with the interpretation.

If we had to make a comparison with univariate data, would the differences in trajectories' locations ("dist" test type) be analogous to the differences in intercept values of univariate slopes? Similarly, are the differences in orientation (correlation) of allometric trajectories ("VC" test type) analogous to differences in slope values (b term in linear regression equation)?

All the best,

Mihajlo

[Mike Collyer]

Dear Mihajlo,

For univariate data, the distance option makes sense, but the vector correlation option does not. The distance is actually the absolute difference between slopes. The vector correlation must be one, because the slopes are divergences on the same axis.  Vector correlation is the cosine of the angle between vectors, so if the vectors exist on a single axis, the angle is always zero. This means vector correlation makes no sense with univariate data.

Best,

Mike

Sent from my iPhone

On Feb 18, 2026, at 2:54 AM, Mihajlo Milic <mihajlo....@gmail.com> wrote:



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[Mihajlo Milic]

Dear Mike,

Thank you so much for your clarification.

Best,

Mihajlo

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