In the Loop Vol. 24 — Combining Whole Person Impairment Figures

A question we field often in Quality Assurance is why a report's total Whole Person Impairment (WPI) figure doesn't match the sum of its parts. If a claimant has a 7% lumbar spine impairment, an 8% finger amputation, and a 15% lower limb impairment, the arithmetic sum is 30% — yet the specialist may correctly report 27%.

The Combined Values Method

The answer lies in the Combined Values Chart of the AMA Guides to the Evaluation of Permanent Impairment, Fifth Edition. Rather than adding figures, each impairment is combined so that a new impairment applies only to the portion of the person that remains unimpaired. Working the example through the chart — 15% combined with 8%, then combined with 7% — yields 27%.

Why Total WPI Cannot Exceed 100%

This is why total WPI can never exceed 100%: the figures are proportional reflections of overall functional loss, not raw numbers to be added indefinitely. Understanding the method helps practitioners explain a figure to a client, defend a compliant report, and recognise when a rating may be inconsistent with the Guides and warrant review.