To make his case, Barkley asserts that the only means by which scientific validity for EEG biofeedback can be established is by controlled research in general, and by double-blind studies in particular. This is simply not true. Very little scientific knowledge is established by double-blind studies. Such studies are uniquely appropriate for testing drug effectiveness. It is not appropriate for biofeedback, in which both the therapist and the patient must be intelligently engaged for the technique to be optimal.
Analogies are educational therapy and psychotherapy.
The efficacy of these modalities cannot be established double-blind. We have to look at outcomes for a statistically significant sample in order to establish efficacy. The effect of smoking on health was established by means of outcome studies. So was the effect of aspirin on heart attack incidence, and the asbestos link to cancer. The question of whether the use of Prozac entails a higher suicide risk than other means of treating depression will be settled with outcome studies, not double-blind studies.