In the adversarial setting of an independent medical evaluation (IME), claimants may be incentivized to exaggerate the severity of their problems. The AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) describes a protocol for assessing impairment associated with chronic pain, including the Impairment Impact Inventory (I3) that consists of 26 items that assess the burden of illness in three domains: pain intensity, interference with activities of daily living, and emotional distress. A study was performed to establish preliminary norms for the I3 and to compare responses of claimants undergoing IMEs with those of treatment-seeking chronic pain patients: 183 patients completed the I3, including fibromyalgia syndrome patients (FMS group), 35 multidisciplinary pain center patients (PC group), and 72 claimants undergoing IMEs. Patients in the latter two groups had a variety of chronic pain problems (and hypothetically may be more likely to exaggerate their problems). The three groups had similar mean scores on the total I3 and for each of the FMS, PC, and IME groups. Results support the hypothesis that participants, in aggregate, do not exaggerate their pain when they undergo IMEs, although some quite possibly do. These results are a step toward establishing a scientific basis for the impairment rating system described in the AMA Guides from consensus-based rules to an evidence-based system for making decisions about impairment.