# [R] How to incorporate interaction terms in MRM function of ecodist library?

Hossm_R hossamesapres at gmail.com
Mon Feb 27 20:28:35 CET 2012

```Hi,

I'm interested in incorporating some interaction terms between my
explanatory variables (distance matrices in this case) when I'm using the
function MRM of the package ecodist. The function is doing a multiple
regression on distance matrices. I can get the function to work perfectly on
my explanatory matrices by adding a (+) sign as known. However, when I try
to use the (*) sign or (:) between two terms that I'd like to check the
interaction for, I get same results as with just additive model. Is there
something that I do wrong?
Thanks,

*For example: *

> mrm.S10z_A<- MRM(Adis ~ S10z.st+Distance.st, nperm=100)
> mrm.S10z_A
\$coef
Int          0.553605282 0.06
S10z.st     -0.002587542 0.86
Distance.st  0.028866573 0.07

\$r.squared
R2        pval
0.004180399 0.060000000

\$F.test
F   F.pval
4.634535 0.060000

> mrm.S10z_A<- MRM(Adis ~ S10z.st*Distance.st, nperm=100)
> mrm.S10z_A
\$coef
Int          0.553605282 0.05
S10z.st     -0.002587542 0.80
Distance.st  0.028866573 0.07

\$r.squared
R2        pval
0.004180399 0.050000000

\$F.test
F   F.pval
4.634535 0.050000

> mrm.S10z_A<- MRM(Adis ~ S10z.st:Distance.st, nperm=100)
> mrm.S10z_A
\$coef
Int          0.553605282 0.05
S10z.st     -0.002587542 0.81
Distance.st  0.028866573 0.11

\$r.squared
R2        pval
0.004180399 0.050000000

\$F.test
F   F.pval
4.634535 0.050000

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