Table 1 American Academy of Neurology evidence classification scheme for determining the yield of established diagnostic and screening tests

This is a new classification scheme developed by the Quality Standards Subcommittee (QSS) for studies related to determining the yield of established diagnostic and screening tests or interventions and is appropriate only when the diagnostic accuracy of the test or intervention is known to be good. Additionally, the abnormality potentially identified by the screening intervention should be treatable or should have important prognostic implications. This classification is different from others currently recommended by the QSS that have been published in recent parameters that relate to diagnostic, prognostic, or therapeutic studies.
1 Statistical sample: A complete (consecutive), random, or systematic (e.g., every third patient) sample of the available population with the disease;
2 Population-based: The available population for the study consists of all patients within a defined geographic region;
3 Non-referral-clinic-based: The available population for the study consists of all patients presenting to a primary care setting with the condition;
4 Referral-clinic-based: The available population for the study consists of all patients referred to a tertiary care or specialty setting. These patients may have been selected for more severe or unusual forms of the condition and thus may be less representative;
5 Objective: An outcome measure that is very unlikely to be affected by an observer’s expectations (e.g., determination of death, the presence of a mass on head CT, serum B12 assays).
Class I: A statistical,1 population-based2 sample of patients studied at a uniform point in time (usually early) during the course of the condition. All patients undergo the intervention of interest. The outcome, if not objective,5 is determined in an evaluation that is masked to the patients’ clinical presentations.
Class II: A statistical, non-referral-clinic-based3 sample of patients studied at a uniform point in time (usually early) during the course of the condition. Most (>80%) patients undergo the intervention of interest. The outcome, if not objective,5 is determined in an evaluation that is masked to the patients’ clinical presentations.
Class III: A selected, referral-clinic-based4 sample of patients studied during the course of the condition. Some patients undergo the intervention of interest. The outcome, if not objective,5 is determined in an evaluation by someone other than the treating physician.
Class IV: Expert opinion, case reports, or any study not meeting criteria for class I to III.