You can cite the No Free Lunch Theorem if you want, but you could also just cite the Modus Ponens (also known as the Law of Detachment, the basis of deductive reasoning), which is the root of the No Free Lunch Theorem.
The No Free Lunch Theorem encompass a more specific idea: the fact that there's no algorithm that can fit all purposes. In other words, the No Free Lunch Theorem is basically saying that there's no algorithmic magic bullet. This roots on the Modus Ponens, because for an algorithm or a statistical test to give the correct result, you need to satisfy the premisses.
Just like in all mathematical theorems, if you violate the premisses, then the statistical test is just empty of sense, and you cannot derive any truth from it. So if you want to explain your data using your test, you must assume that the required premisses are met, if they're not (and you know that), then your test is dead wrong.
That's because scientific reasoning is based on deduction: basically, your test/law/theorem is an implication rule, which says that if you have the premisse A
then you can conclude B
: A=>B
, but if you don't have A
, then you can either have B
or not B
, and both cases are true, that's one of the basic tenets of logical inference/deduction (the Modus Ponens rule). In other words, if you violate the premisses, the result doesn't matter, and you cannot deduce anything.
Remember the binary table of implication:
A B A=>B
F F T
F T T
T F F
T T T
So in your case, to simplify, you have Dependent_Variables => ANOVA_correct
. Now, if you use independent variables, thus Dependent_Variables
is False
, then the implication will be true, since the Dependent_Variables
assumption is violated.
Of course this is simplistic, and in practice your ANOVA test may still return useful results because there is almost always some degree of independence between dependent variables, but this gives you the idea why you just can't rely on the test without fulfilling the assumptions.
However, you can also use tests which premisses are not satisfied by the original by reducing your problem: by explicitly relaxing the independency constraint, your result may still be meaningful, althrough not guaranteed (because then your results apply to the reduced problem, not the full problem, so you cannot translate every results except if you can prove that the additional constraints of the new problem do not impact your test and thus your results).
In practice, this is often used to model practical data, by using Naive Bayes for example, by modelling dependent (instead of independent) variables using a model that assume independent variables, and surprisingly it works often very well, and sometimes better than models accounting for dependencies. You can also be interested by this question about how to use ANOVA when the data doesn't exactly meet all expectations.
To summary: if you intend to work on practical data and your goal is not to prove any scientific result but to make a system that just works (ie, a web service or whatever practical application), the independency assumption (and maybe other assumptions) can be relaxed, but if you're trying to deduce/prove some general truth, then you should always use tests which you can mathematically guarantee (or at least safely and provably assume) that you satisfy all premisses.