A method for the identification of treatments and preventative agents for brain aging, subjective cognitive impairment (SCI), mild cognitive impairment (MCI), Alzheimer's disease (AD) and other degenerative dementias, the method including (a) the identification of the diagnosis and stage of the subject, (b) the identification of the duration of the stage of the condition and/or disorder, (c) the identification of prognostic markers based upon a formula incorporating the duration of the condition and/or stage, (d) the prospective separation of prognostic subgroups based upon outcome wherein the outcome is defined in these conditions as progression to a subsequent stage or stages, (e) the employment of a putative prognostic marker for an appropriate period of time, based upon the formula incorporating the duration of the condition and/or stage, (f) the application of in vivo, methodology specific techniques, in conjunction with stage specific prognostic subgroups, for the appropriate time period, for the identification, prospectively, of useful markers, (g) the employment of these markers to identify useful therapeutic agents for prevention and treatment.