1. Labor Code 4663 Apportionment states that:
   • Apportionment of permanent disability shall be based on causation.
   • Any physician who prepares a report addressing the issue of permanent disability due to a claimed industrial injury shall in that report address the issue of causation of the permanent disability.
   • In order for a physician's report to be considered complete On the issue of permanent disability, the report must include an apportionment determination ...
   • An employee who claims an industrial injury shall, upon request, disclose all previous disabilities or physical impairments.
2. Certain injuries or illnesses are not subject to Apportionment
   • Subdivisions (a), (b), and (c) shall not apply to injuries or illnesses covered under Sections 3212, 3212.1, 3212.2, 3212.3, 3212.4, 3212.5, 3212.6, 3212.7, 3212.8, 3212.85, 3212.9, 3212.10, 3212.11, 3212.12, 3213, and 3213.2.
   • Note: This is the "anti-attribution" clause, meaning apportionment per LC 4663 (a), (b) & (c) doesn't apply to injuries/illnesses covered by these sections.
   • The statutes cited in LC 4663(e) hold that certain injuries & conditions (including hernia, heart trouble, pneumonia, cancer, TB, MRSA, blood-borne infectious diseases, biochemical substances, meningitis, skin cancer, Lyme disease, and lower back impairment) that occur to certain classes of employees (i.e., firefighters, prison guards, CHP, law enforcement officers, etc.) are presumed industrial.
   • LC 4663(e) makes them not subject to apportionment.
3. Things the doctor should Address or Include when Apportioning
   • An explanation of the nature of the disease process or condition to which apportionment is applied;
   • An explanation of how and why it is causing permanent disability at the time of the evaluation;
   • An explanation of how and why it is responsible for the percentage of disability to which apportionment is applied; and
   • An explanation of the causal connection between that to which apportionment is applied and the industrial injury.
   • Any explanation of the "why" (rationale) must be internally consistent.
   • Avoid using words like "fair" when percentages are selected (use "reasonably medically probable").
   • Understand the difference between risk factors for development of a condition or injury (as a causative factor of injury) and apportionment of disability.
   • If the doctor is unable to include an apportionment determination, they must explain why. This will require consultation with other physicians or referral to another physician from whom the IW is authorized to seek treatment or evaluation.
   • Understand the concepts in the Benson case and provide detailed explanation.
   • Be aware of situations in which Benson may be a factor (i.e., more than one injury claim, prior injuries with or w/o adjudicated levels of disability/impairment, etc.).
   • Under Benson, the doctor must provide a detailed discussion as to what is the actual disability/ impairment attributable to each separate injury and state the reasons for their opinions.
   • If the doctor is unable to separate the disability or impairment attributable to each separate injury, they must state why and provide a well-reasoned discussion of overall disability/impairment that meets all criteria for substantial medical evidence
   • All opinions on apportionment should be couched in terms of reasonable medical probabilities and be based upon knowledge, expertise and/or experience