This nationwide data come from a careful statistical analysis by analysts in the Department of Consumer and Business Services in the state of Oregon. "The study is based on methods that put states’ workers’ compensation rates on a comparable basis, using a constant set of risk classifications for each state." States are ranked based on workers' compensation costs after adjustments to make them comparable. The states are ranked from high to low, with one indicating the highest premium rate index per $100 of payroll.
According to the 2016 Oregon Workers’ Compensation Premium Rate Ranking Summary, "Premium rate indices are calculated based on data from 51 jurisdictions, for rates in effect as of Jan. 1, 2016. The 2016 median value is $1.84, which is a drop of less than 1 percent from the $1.85 median of the 2014 study. Oregon’s premium rate index is $1.28 per $100 of payroll, or 69 percent of the national median. National premium rate indices range from a low of $0.89 in North Dakota, to a high of $3.24 in California. There were 21 states that had an index rate that was within plus or minus 10 percent of this benchmark value. In the upper part of the rate distribution, 12 states had index rates higher than 110 percent of the median, while 18 states were below 90 percent of the median. For an interactive map of the state rankings, click here."
Notes from the 2018 Report: "Starting with the 2008 study, when two or more states’ Index Rate values are the same, they are assigned the same ranking. The index rates reflect adjustments for the characteristics of each individual state’s residual market. Rates vary by classification and insurer in each state. Actual cost to an employer can be adjusted by the employer’s experience rating, premium discount, retrospective rating, and dividends."