Statutory Framework
California permanent disability ratings are governed by Labor Code sections 4660-4664. The calculation converts medical impairment assessments into disability percentages that determine benefit amounts.
Key Components
Whole Person Impairment (WPI)
Physicians assess impairment using the AMA Guides to the Evaluation of Permanent Impairment (5th Edition for most California cases). The WPI represents the percentage of whole body function lost due to the injury.
Occupational Adjustments
The WPI is adjusted based on occupational factors:
Occupation Group. Jobs are classified into groups (A through L) based on physical demands. Higher-demand occupations receive larger adjustments.
Variant. Within each occupation group, specific job variants may apply additional adjustments.
Age Adjustment
The injured worker's age at the time of injury affects the rating. Older workers generally receive higher adjustments, reflecting reduced adaptability.
Future Earning Capacity (FEC)
For injuries after January 1, 2013, the FEC adjustment modifies ratings based on projected impact on earning capacity. This is calculated using a formula that considers the nature of the disability and occupation.
Combining Multiple Impairments
When an injury involves multiple body parts, the Combined Values Chart (CVC) is used. This chart uses a specific formula to combine individual ratings:
A + B(1-A) = Combined Value
For example, a 20% rating combined with a 15% rating yields approximately 32%, not 35%.
The PDRS
The Permanent Disability Rating Schedule (PDRS) provides the lookup tables and adjustment factors. The current schedule (2005 PDRS) applies to most cases, with modifications for post-2013 injuries.
Apportionment
Labor Code section 4663 requires apportionment of disability to causation. If pre-existing conditions contributed to the current impairment, the rating may be reduced accordingly.
Calculation Tools
Manual PD calculations require cross-referencing multiple tables and applying several formulas. The Glass Box PD calculator automates this process, showing each step:
6. Display final rating with full documentation
Accuracy Verification
Calculation outputs should be verified against the statutory framework. The Glass Box calculator displays all intermediate values, allowing step-by-step verification against the PDRS tables.