It's a statistical measure, used to compare how similar two populations are.

Actually, that's a bit of a given. All statistics are about comparing how similar or related two populations are. To help us tell if any differences or relationships truly exist.

The most powerful and commonly used (and arguably easy to understand) statistical comparisons are using a kind of data called 'parametric'. These follow certain rules. That most values will be in the middle of the range, for instance, in what might be shaped a "Bell" curve (Gaussian, for those in the know).

Spearman's rho is a kind of

Much more could be said, but no space here. Read more on answers.com.

Actually, that's a bit of a given. All statistics are about comparing how similar or related two populations are. To help us tell if any differences or relationships truly exist.

The most powerful and commonly used (and arguably easy to understand) statistical comparisons are using a kind of data called 'parametric'. These follow certain rules. That most values will be in the middle of the range, for instance, in what might be shaped a "Bell" curve (Gaussian, for those in the know).

Spearman's rho is a kind of

**non**-parametric way of comparing populations -- where data values don't cluster in the middle of the range or don't occur on an unbroken continuum. Spearman's rho is appropriate if the data from two different populations can be put into order, though - what's called ordinal data. This makes it possible to see whether the data respond together (as one set of values changes, so might the other).Much more could be said, but no space here. Read more on answers.com.