<p>Usage of <a href="http://en.wikipedia.org/wiki/Validity_%28statistics%29" rel="nofollow">'validity'</a> tends mostly to refer to the sense in used in psychometrics, education and other social sciences and often refers to specific tests or instruments to measure some particular thing ("IQ-test validity"). 'Validation' is usually used in a different (though not entirely unrelated) sense relating to the properties of particular statistical models - model-validation, predictive-validation, cross-validation.</p>

<p>While occasionally they're used to talk about the same thing (like when a education researcher talks about <em>validation</em> of an instrument or someone who has just done some model validation talks about model-validity), usually the two are used quite differently.</p>

<p>As such I <em>don't</em> think these should be synonyms. </p>
