The most important factor is to control for hazard mix. Without a control for this, you don’t have a valid comparison of what comparable employers would pay. There is no other current data series that controls for hazard mix across all 50 states.
Oregon's class mix is actually quite similar to the countrywide mix in the classifications that have the largest weight in the study, so the rankings would change very little if a countrywide mix was used. We have verified this by comparing our findings of relative rates to an independent source of rate comparison data for 27 states that uses countrywide data as a benchmark. The two data series produce very similar results, with the same states shown as higher and lower rates.