Workers’ Compensation · Primary-source case analysis

Escobedo: Apportionment Requires Reasoned Substantial Medical Evidence

By Aneeta Mishra and Timothy Chan

Published April 14, 2026 · Updated October 18, 2026

Decision: Escobedo v. Marshalls, No. GRO 0029816 (WCAB Apr. 19, 2005) (en banc).

A doctor’s percentage must be explained, but a supported percentage need not be rejected merely because the worker had no earlier symptoms. In Escobedo, the WCAB affirmed a 27-percent permanent-disability award after accepting a physician’s reasoned allocation of half the disability to preexisting knee arthritis. The en banc decision distinguishes a condition that exists from one that actually causes permanent disability. Escobedo, slip opinion, pages 1–5, 20–22.

Causation of disability

The Board distinguished causation of the industrial injury from causation of permanent disability. Section 4663 asks what approximate percentage of the permanent disability was directly caused by the industrial injury and what percentage was caused by other factors.

Factors beyond prior awards

Other factors can include pathology, asymptomatic prior conditions, and prophylactic work restrictions that would not necessarily have supported apportionment under earlier law. The key is whether substantial medical evidence establishes that the factor actually caused permanent disability.

What substantial evidence requires

A physician must use reasonable medical probability, pertinent facts, an adequate examination and history, and reasoning that connects those facts to the approximate percentages selected. A bare conclusion is not enough. Here, the evaluator connected the MRI and x-ray arthritis findings, the injury mechanism and the timing of symptoms in both knees to his allocation. The Board found his explanation substantial; it did not announce that arthritis always supplies a 50-percent reduction. Escobedo, slip opinion, pages 20–22.

Burdens and adjudication

The applicant bears the burden of proving overall permanent disability and its industrial share; the defendant bears the burden of proving the share caused by other factors. A supplemental report or deposition can test the reasoning. Even a report written before the 2004 reform could be used if it actually met the new standard; its date alone did not make it sufficient or insufficient. Escobedo, slip opinion, pages 9–11, 22. This page describes the 2005 holding, not every later statutory exception to apportionment.

Key takeaways

• Apportionment concerns causation of permanent disability, not simply causation of injury.
• An “other factor” must actually contribute to disability.
• Approximate percentages require a reasoned medical explanation.
• The WCAB must reject speculative or conclusory allocations.