Why does Mathematica not return "True" for Correlation function equality expression?

Question

I wish to check the invariance property of correlation. As described in this wiki section Wiki - Mathematical Properties of Correlation. A quote from the Wiki page I wish to test is below.

That is, we may transform X to a + bX and transform Y to c + dY, where a, b, c, and d are constants with b, d > 0, without changing the correlation coefficient.

Correlation[{a + b *x1, a + b*x2}, {c + d*y1,c+ d* y2}] ==Correlation[{x1, x2}, {y1, y2}]
Refine[%, {{a, b,c, d, x1, x2, y1, y2} \[Element] Reals, {b, d} > 0}] 

From the output, I believe I can see that these are in fact equal if I factor and cancel b and d. However, I would have hoped that Mathematica would have simply returned the result "True".

Why did Mathematica not return "True"?

Answer 1

Correlation[{a + b x1, a + b x2}, {c + d y1, c + d y2}]==Correlation[{x1, x2}, {y1, y2}]

FullSimplify gives the expected result:

Assuming[Variables[%] ∈ Reals && And @@ Thread[{b, d} > 0], FullSimplify @ %]

True