The generally accepted definition of autism spectrum disorder is that in DSM-V. This physiological test is compared against ASD diagnoses based on DSM-V, and based on that comparison, the accuracy of the test (for the given sample tested) is calculated.

As more is known about the condition, the diagnostic criteria listed in the DSM could be updated, which would mean that this test would then need to be evaluated again. But that doesn't prevent its current accuracy being measured.