A new RAND Corporation study, Examining the Impact of Senate Bill 1160 on Utilization Review and Medical Treatment in California Workers’ Compensation, offers the first empirical look at whether a decade-old reform aimed at speeding up early medical care for injured workers actually worked. The report, published July 20, 2026 and sponsored by the California Department of Industrial Relations (DIR), finds that the 2016 law delivered a modest, measurable improvement in one key treatment area — but that utilization review (UR) was rarely the barrier the law was designed to remove in the first place.

Senate Bill 1160, enacted in 2016 and effective for injuries on or after January 1, 2018, exempted certain treatments provided in the first 30 days after a work injury from prospective UR — the process by which claims administrators approve, modify, or deny a treatment recommendation before care is delivered. Under the law, treatment for an accepted, compensable injury that is consistent with the Medical Treatment Utilization Schedule (MTUS) and delivered by a provider in the employer’s medical provider network is automatically authorized during that first month, without needing prospective sign-off. Claims administrators can still review those treatments retrospectively to check MTUS consistency, and a provider found to have a pattern of inconsistent care can be required to go back through prospective UR. The exemption reaches common early-stage treatments such as physical therapy and initial X-rays, but Labor Code section 4610(c), as amended by SB 1160, carved out several categories that remain subject to prospective UR even in the first 30 days, including surgery, pharmaceuticals, imaging other than X-rays, psychological treatment, home health care, and certain injections. All employers remain required to maintain a UR plan consistent with Labor Code section 4610 and its implementing regulations at 8 California Code of Regulations section 9792.6 et seq.

To evaluate the law’s effects, the RAND team — led by Stephanie Rennane and Michael Dworsky — combined four data sources: individual-level treatment-authorization records from two large claims administrators covering Northern and Southern California, statewide Independent Medical Review (IMR) data from DIR, DIR’s own UR audit reports, and medical billing data from the California Workers’ Compensation Information System (WCIS). The study period ran from January 2017 through January 2024, covering a full year before the law’s effective date and six years after. Researchers used interrupted time-series models to test for statistically significant shifts in UR approval rates, receipt of guideline-concordant care, and time to first treatment, before and after the January 1, 2018 implementation date.

The headline finding is that UR approval rates for treatment requested in the first 30 days after injury were already high before the law took effect — consistently above 90% at both claims administrators the researchers studied — and did not change in any statistically meaningful way afterward. That held true across nearly every treatment category the researchers examined, including physical therapy, imaging, surgery, and durable medical equipment. Approval rates for requests submitted later in a claim, by contrast, ran several percentage points lower throughout the study period, and treatment categories that SB 1160 left subject to full prospective review — imaging other than X-rays, injections, and psychiatric or psychological services — consistently showed the lowest approval rates of all, in the 70% to 90% range depending on the data source and category. In other words, the study suggests UR was rarely denying or slowing early, routine care even before SB 1160 removed the requirement to review it in advance. The researchers also found that many claims administrators already ran informal “prior authorization” programs that let common early treatments bypass the formal request-for-authorization process entirely, further reducing the friction SB 1160 was designed to eliminate.

Where the law did leave a measurable mark was physical therapy. Among injured workers with diagnoses for which physical therapy is clinically recommended, the odds of receiving it within 30 days of injury rose 13% after SB 1160 took effect, and the average time to a first physical therapy visit within that window dropped from 13.4 days before the law to 11.9 days after. Guideline-concordant use of braces and other immobilizers also rose modestly, with 8% higher odds of receipt within 30 days, though the timing of that care didn’t measurably speed up. Effects elsewhere were smaller and more mixed: receipt of guideline-concordant X-rays didn’t change significantly, consistent with X-rays already being commonly pre-authorized before the law; guideline-discordant acupuncture — treatment given for diagnoses where it isn’t recommended — actually rose 24% in relative terms after the law, though it remained rare in absolute terms, staying under 3% of cases throughout the study; and MRI use in the first 30 days declined slightly even though MRIs were explicitly excluded from SB 1160’s reduced-review provisions, a pattern the researchers attribute to unrelated trends rather than the law itself. Overall, the study concludes that SB 1160’s clearest, most defensible effect was on physical therapy access, and that the modest size of the effects generally reflects a system in which common early treatment was already flowing fairly freely before the reform.

The report closes with three recommendations for DIR and the Legislature. First, DIR should systematically document the informal prior-authorization programs claims administrators already run, since the report found meaningful, unexplained variation in which treatments different administrators pre-approve without any authorization request at all. Second, because most UR activity and most denials happen well after the first 30 days — and because treatments SB 1160 left fully subject to prospective review, particularly imaging and psychological services, have distinctly lower approval rates — the report suggests the Legislature examine whether reduced-review treatment could be extended further into a claim, or targeted more by treatment type and evidence strength than by a fixed 30-day window. Third, the researchers recommend DIR build out its planned systemwide UR database with standardized diagnosis and procedure codes and consistent claim identifiers, arguing that the absence of any comprehensive, uniform dataset on UR decisions was itself one of the central limitations of this study and remains an obstacle to evaluating future reforms.