An individual's impairment rating is decided by a series of condition- or injury-specific tests performed by a qualified physician. Impairment ratings may be measured in percentages, degrees or categories, depending on a state's rating system.
Impairment ratings are used to describe an individual's level of disability, as well as predict loss of future income. Impairment ratings are assessed by a patient's personal physician or physician who specializes in worker's compensation cases. Ratings may also be assessed by an independent medical examiner, depending on a state's requirements.
Tests for impairment ratings are noninvasive tests administered on body parts that have been injured and are possibly disabled. Each injured body part is tested separately. Impairment ratings may be assigned to each individual body part or combined into an overall impairment rating, depending on a state's disability program's guidelines.
The majority of states use the American Medical Association's "Guides to the Evaluation of Permanent Impairment" in order to determine a disability rating. Disability ratings vary from state to state, depending on which edition of this book is used by a state to determine impairment ratings, as each edition calculates impairment ratings differently. Several states have established independent guidelines to determine impairment ratings. Some states do not have established guidelines to be followed when determining disability.