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I have heard the term "orthogonal * validation" used recently. It was used in the context of experimental platform testing. What does this mean? I cannot find anything on it in literature or Wikipedia.

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Could you provide a reference to what you heard or elaborate on the context a little? –  whuber Jun 17 '12 at 13:26
I believe it was in the context of microarray platform comparison or analytical tool comparison. –  user1447630 Jun 17 '12 at 18:09
Google searching reveals that "orthogonal validation" in an experimental context can mean different things in different fields. "Orthogonal" is often applied loosely to anything that metaphorically can be thought of as "at right angles." The metaphor extends to statistics (uncorrelated variables are at "right angles" to each other), design of experiments (orthogonal designs and polynomials), and to physical realms with orthogonal arrays of cells (in proteomics) and orthogonal plowing patterns (in agriculture). The technical meanings differ radically, which is why some context is crucial. –  whuber Jun 18 '12 at 14:32

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Basically, it would seem that people use orthogonal as a synonym for independent. So, for orthogonal validation read independent validation The validity of equating orthogonality with independence is discussed here such that "if X and Y are independent then they are Orthogonal" but "the converse is not true".

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That seems to correspond with what I heard. It's not immediately obvious that independence and orthoganality are interchangeable. –  user1447630 Jun 17 '12 at 18:29
The converse is true when the variables are jointly normally distributed. Speaking of variables, it's not totally clear to me what's orthogonal to what in this context but that may just be because I'm not familiar with the application. –  Macro Jun 17 '12 at 18:34
@Macro presumably the different methods of validating some experimental platform are orthogonal? That's how I interpret it anyway. Perhaps OP can confirm. –  user1202664 Jun 17 '12 at 18:37
@user1447630 The answer you checked is wrong. Orthogonality in statistics has nothing to do with orthogonal validation. Check the links out that I gave you for the correct description. A few are abstracts that don't give complete nswers but others do. Also the statistical term orthogonal is not the same as independent. It means that variables are uncorrelated and uncorrelated does not always mean indpendent. –  Michael Chernick Jun 17 '12 at 18:41
@MichaelChernick, then can you solve the mystery and tell us all what it is? I'm still not sure, even after looking at both of the answers here. –  Macro Jun 17 '12 at 18:47

An orthogonal method is an additional method that provides very different selectivity to the primary method. The orthogonal method can be used to evaluate the primary method. For example, two methods can be used to investigate protein aggregation 1) size-exclusion chromatograph or an orthogonal method such as 2) analytical ultracentrifugation. Both methods are independent approaches that can answer a question such as "is my protein aggregated?"

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This "orthogonal" word is rather fashionable part of slang in recent EMA/FDA guidelines. Literary means that something crossed at right angle, so more intuitively understood substitute is "cross-over methodology" i.e. two essentially different methods used to measure the same value ("crossing-point"), so the measurement is reliable. Latin rules again :-)

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