# Can I test for correlation between variables before standardize them?

What I want to do is to construct GLMM’s to evaluate resource selection, and I have a set of variables (some representing distances and others representing % of land cover).

Can I test for correlation between variables before standardize them? I am not quite sure what should I do first.

Can I test for correlation between variables before standardize them? I am not quite sure what should I do first.

Correlation will be the same regardless whether you calculate it before or after standardization. To see this, it is enough to know that correlation is invariant to scale. Take $b \in \mathbb{R}$ and $a>0$, then

The first equality is a definition.
The second uses the property that covariance as well as variance are invariant to location shifts.
The third uses the properties of covariance and variance with respect to multiplication by a constant.
The fourth uses the fact that $a>0$.
The fifth just cancels out the multipliers.
The sixth is again a definition.

This covers standardization, which is subtracting the mean and dividing by the standard deviation (a positive number).