Apportionment — industrial versus other causes

What the Appeals Board did with this

Newest released decisions that turned on this issue. Each quotes the passage it turned on and links to the official PDF. Litigated tail — not a win rate, not a settlement value.

• ADJ11349173 · 2026-06-26 · Riverside District OfficeApportionmentdefendant prevailed

  Determinative passage · p.6Here, while the WCJ relied upon the submitted medical reporting from the AME/PQMEs for her findings on permanent disability, she found that the reports of Drs. Gupta and Wood are not substantial evidence on the issue of apportionment.

  The WCJ and WCAB found that the opinions of Drs. Gupta and Wood on apportionment lacked substantial medical evidence and reasoning, thus defendant did not meet its burden of proof on apportionment.

  Official decision · page 6 →
• ADJ19328573 · 2026-06-26 · Sacramento District OfficeApportionmentapplicant prevailed

  Determinative passage · p.13(Exhibit CC, Sean Robinson, M.D., March 4, 2025, PDF p. 64, emphasis added.) The statements provided do not explain how the identified factors caused applicant's

  The Appeals Board found that the medical opinion on apportionment by Dr. Sean Robinson was not substantial evidence due to lack of adequate explanation and reliance on speculation, thus rejecting apportionment and awarding permanent disability without apportionment.

  Official decision · page 13 →
• ADJ9518215 · 2026-06-02 · Van Nuys District OfficeApportionmentapplicant prevailed

  Determinative passage · p.1Defendant seeks reconsideration of the Findings and Award (F&A) dated February 18, 2026, wherein the workers' compensation arbitrator (WCA) found, in relevant part, that while employed on March 4, 2014 by defendant as a custodian, applicant sustained injury arising out of and occurring in the course of employment (AOE/COE) to the lumbar spine, cervical spine, bilateral shoulders, headaches, vertigo and dizziness, internal, heart, sleep, fibromyalgia, and sexual dysfunction resulting in 100% permanent disability without apportionment.

  The WCAB found that the applicant sustained injury arising out of and in the course of employment and is 100% permanently disabled without apportionment, relying on substantial evidence including medical and vocational expert reports. Defendant's challenge to apportionment based on Dr. Levine's findings and sub rosa video footage was rejected as the evidence supported the applicant's total disability without apportionment.

  Official decision · page 1 →
• ADJ15615310 · 2026-06-01 · Santa Ana District OfficeApportionmentapplicant prevailed

  Determinative passage · p.15Dr. Mack's apportionment opinion fails to satisfy the requirements as set forth in Escobedo6. His analysis relies primarily on the timing of Applicant's employment and the existence of pre-existing conditions, without explaining "how and why" those conditions are causing permanent disability at the time of the evaluation. As explained in Escobedo, a medical opinion on apportionment must do more than state percentages. It must explain the causal relationship between the industrial injury and the permanent disability and separately explain how and why nonindustrial factors are responsible for a portion of that disability. Dr. Mack's reports do not provide this required analysis. The deficiency is also apparent with respect to the cubital tunnel syndrome. While Dr. Mack relates this condition to the elbow pathology, he does not explain why 50% of the resulting disability is attributable to nonindustrial factors or identify what those factors are. A mere medical relationship between conditions does not establish apportionment. Because Defendant bears the burden of proof on apportionment, and because the medical evidence offered does not constitute substantial evidence, the Court is not permitted to rely upon it. Accordingly, an unapportioned award is warranted.

  The Appeals Board found Dr. Mack's apportionment opinion was not substantial evidence as it lacked required detailed explanation and reasoning, thus denying apportionment and awarding an unapportioned permanent disability.

  Official decision · page 15 →
• ADJ14680333 · 2026-05-29 · Pomona District OfficeApportionmentdefendant prevailed

  Determinative passage · p.12Based on the record before us, we discern no reason to disturb our prior Decision and will therefore deny defendant's Petition.

  The Board found that the medical opinions on apportionment lacked substantial evidence because they failed to provide adequate medical reasoning connecting the impairment to other factors, thus denying defendant's petition for reconsideration on apportionment.

  Official decision · page 12 →
• ADJ16112682 · 2026-05-19 · Oakland District OfficeApportionmentapplicant prevailed

  Determinative passage · p.3The WCJ's opinion found that apportionment was not appropriately addressed per the standards outlined in Escobedo v. Marshalls (2005) 70 Cal.Comp.Cases 604, 611 (en banc) because the physician did not clearly outline the pre-existing conditions nor did he adequately address with particularity how those conditions caused the current impairment. He accepted the QME's opinion that the impairment to the right and left shoulder should be added instead of combined. The WCJ also found that the correct occupational code is 330 based on the job description provided (Defendant's Exhibit A.)

  The WCJ found that the QME Dr. Hughes did not adequately explain the apportionment of pre-existing conditions to the current impairment as required by Escobedo, and thus rejected the apportionment and rated permanent disability at 76% without apportionment based on Dr. Reiter's opinion.

  Official decision · page 3 →
• ADJ22325507 · 2026-05-11 · Los Angeles District OfficeApportionmentdefendant prevailed

  Determinative passage · p.3II. In addition to the reasons stated by the WCA, we note the following observations. The WCA, in significant part, based the opinion in this matter upon the recent panel decision of Canto Shadoan v. City of San Diego. (91 Cal.Comp.Cases 352, 2025 Cal.Work.Comp. P.D. LEXIX 435 (writ den.).). On April 29, 2026, the Fourth District Court of Appeal denied review in Canto Shadoan with an unpublished opinion expressing agreement with the logic of the case. The WCA did not find apportionment based upon causation in this matter. Both of applicant's disabilities were rated using the exact same method contained in the AMA Guides, which was range of motion. Both AMEs in both cases found that applicant's impairment was 100% industrial in accordance with section 4663(e). Both disability awards are based upon a finding of 100% industrial causation.

  The WCAB found that apportionment under section 4664 by the subtraction method is allowed despite the anti-attribution clause of section 4663(e) because the prior award overlaps the present award and both use the same AMA Guides rating method.

  Official decision · page 3 →
• ADJ12317646 · 2026-05-04 · Lodi District OfficeApportionmentapplicant prevailed

  Determinative passage · p.7nonindustrial apportionment of impairment for the lumbar spine, bilateral hips, heart, and hernia for the cumulative injury claim ending on May 10, 2019 and that the opinions of Drs. Amster and Schmitz on the issue of apportionment are not written in accordance with the requirements outlined in Escobedo and Gatten given their lack of specificity, lack of reasoning, and lack of supporting evidence.

  The Appeals Board found that defendant did not meet the burden of proving nonindustrial apportionment with substantial medical evidence, as the opinions of Drs. Amster and Schmitz lacked specificity, reasoning, and supporting evidence as required by Escobedo and Gatten.

  Official decision · page 7 →