Dear Callie,
I am not sure I fully understand your question. Perhaps you could provide details as to how your 20 projectile points are transformed into data, how the pairwise rotation of two configurations was applied to your 20 projectile points, and what is the aim of the test.

Now, let's assume for the sake of argument that you have converted your projectile points into data as a set of n 2D landmarks (in the case of circle you would have used the same amount of points to form a circle). Let's also assume that you have used as starting point for your PROTEST two of these configuration of landmarks (i.e., the matrix with n rows and 2 columns containing the x,y coordinates of each landmark; one matrix for one projectile point, the other for another projectile point).

If the above were true and based on the way the procedure works (in my case, I'm referring to the description in Peres-Neto & Jackson 2001 - Oecologia), I think a reasonable expectation, for two quite similar shapes, would be: - that after Procrustes superimposition, the x,y coordinates of corresponding points/landmarks would be extremely similar, giving a very low "Procrustes sum of squares (m12)" - that randomly exchanging the order of the points in one of the two configurations would basically never give you a "Procrustes sum of squares (m12)" as small (because, in lay terms, if in one of the two landmark configurations you exchange the position of two or more of the landmarks, the two shapes will not match as precisely as your original configuration)

Blake has given you a potential explanation of why a specific value, perhaps my hypothetical scenario (if it applies) can give you a hint on why that is always the same.

If the hypothetical scenario above were correct, I would see no special issue with the value being always the same (and extremely low). In that case, however, there might be an issue with the practical utility of performing the test in the first place.

I hope this helps,
Carmelo




Il 16/01/2018 7:51 PM, Callie Diduck ha scritto:

Hi,

I am wondering if any one can help me. I have been running a Procrustes Rotation of Two Configurations and PROTEST using the vegan package in R. The Procrustes seem to be working but I am having an issue with the results of the PROTEST and the correlation values.

I am getting identical p values every time I run the script. I have a sample size of 20 projectile points and every time I run the statistics my p value is equal to 0.00009999. I ran a test and I compared a circle to one of my projectile points and I still got a p value of 0.00009999.

Here are the results for the test of the projectile point compared to a circle:


Procrustes sum of squares:

1.817e+04

Call:

protest(X = p730, Y = pTest, permutations = 10000)

Procrustes Sum of Squares (m12 squared):        0.06296

Correlation in a symmetric Procrustes rotation: 0.968

Significance:  9.999e-05

Permutation: free

Number of permutations: 10000


If anyone has any idea of why this could be happening or how to fix it that would be greatly appreciated.

Thanks

Callie Diduck

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