Under AMA Guides apportionment is based on?

• A. Causation
• B. Medical report of treating physician
• C. Pre-existing disability
• D. Informal rating

Answer: (A)

Apportionment under the AMA Guides is about causation—the portion of a claimant’s impairment that is caused by the work-related injury versus non-work-related factors (such as a pre-existing condition). Evaluators determine how much impairment stems from the industrial factor and assign that portion to workers’ compensation, while the remainder is attributed to non-industrial factors. For example, if total impairment reflects contributions from both a pre-existing condition and the work injury, the Guides guide you to apportion the impairment according to each factor’s causal contribution. While a treating physician’s opinion and the presence of a pre-existing disability influence the assessment, the fundamental basis for apportionment is the causal relationship between the injury and impairment, not merely a medical report or an informal rating.