Objectives: To examine the association between impairment ratings and earnings losses.
Methods: We conducted a case-control study of 21,663 workers' compensation claimants in California with impairment ratings under the AMA Guides, fifth edition. Earnings losses represented the percent difference between the earnings of cases and controls 3 years after disability onset.
Results: Impairment ratings were strongly associated with earnings losses: losses for ratings of 1, 10, and 20 were 9.0%, 21.9%, and 34.6%, respectively (P < 0.01). Losses differed significantly across body regions. For example, losses were 21.0% for spine impairments compared with 18.4% overall (P = 0.014).
Conclusions: Impairment ratings are accurate predictors of disability severity on average, but their ability to measure disability could be improved with additional information on how the relationship between ratings and earnings loss varies according to patient and injury characteristics.