dissenting.
[¶ 17] I respectfully dissent from the Court’s conclusion that the hearing officer erred when adopting the independent medical examiner’s (IME) opinion that Smart suffers 40% permanent impairment because the IME consulted sources outside the American Medical Association, Guides to the Evaluation of Permanent Impairment (4th ed. 1993) (AMA Guides) and in particular the percentages outlined in the second edition of the AMA Guides. In my view, neither the Workers’ Compensation Act nor Board Rules mandate that percentages of permanent mental impairment be calculated by referring only to numeri*762cal percentages set forth within the fourth edition. Evaluators making this medical determination should not be precluded from looking to valid sources outside of the fourth edition for guidance.
[¶ 18] The editors of the fourth edition recognized the inherent limitations on a doctor’s ability to accurately measure permanent impairment that results from mental and behavioral conditions. AMA Guides at 301. Instead of delineating standard percentages for assignment to specific classifications of permanent mental impairment, they directed evaluators to use their best judgment based on clinical impressions when it is essential to make an estimate, stating:
Physicians, of course, must often make judgments based more on clinical impressions than on accurate, objective, analytic empiric evidence. In those circumstances in which it is essential to make an estimate, the ordinal or numeric scale might be of some general use....
Eventually, research may disclose direct relationships between medical findings and percentages of mental impairment. Until that time, the medical profession must refine its concepts of mental impairment, improve its ability to measure limitations, and continue to make clinical judgments.
Id.
[¶ 19] Moreover, the fourth edition of the AMA Guides defines impairment as “an alteration of an individual’s health status,” and directs that impairment be assessed by medical means because it is a medical issue. Id. at 1. Doctors who use their best clinical judgment will consult a variety of sources to medically assess permanent mental impairment. Therefore, when arriving at a numerical percentage, it does not violate the Board’s admonition to use the fourth edition when a doctor seeks guidance from other reliable medical sources outside the fourth edition. In fact, the fourth edition encourages this position by referring to other rehable resources such as the Social Security Administration, Listing of Impairments, Mental Disorders, 20 C.F.R. § 404, App. 1 (1985), and the World Health Organization, Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Death: International Classification of Diseases (1978), when classifying mental and behavioral conditions. Id. at 291-302.
[¶ 20] Limiting the evaluator to referencing numerical percentages established within the fourth edition serves no useful purpose and is counter to the rationale of the majority’s opinion here and in Harvey v. H.C. Price Co., 2008 ME 161, 957 A.2d 960. A reasonable evaluator could conclude that the assessment method sanctioned in Harvey and enshrined in this case, in which the IME used the percentages in chapter four of the fourth edition applicable to neurological conditions with mental and behavioral features, is unsound. The IME in this case noted that while impairment from such neurological conditions may be similar to mental and behavioral impairment in presentation, such impairment may also be very different “in etiology, treatment and prognosis.” Accordingly, she reasonably declined to apply the percentages in chapter four of the fourth edition and looked instead to other sources containing numerical percentages intended to apply to mental and behavioral conditions.
[¶ 21] It is consistent with the fourth edition for evaluators to use sound medical judgment, and sound medical judgment is based on the reservoir of knowledge, skill and wisdom each doctor has retained from her particular training, education and ex-*763perienee. The IME’s opinion that Smart suffers 40% permanent impairment as a result of his mental stress injury is not incompatible with the fourth edition of the AMA Guides, and the hearing officer’s decision to adopt that opinion should be affirmed.