NCCI Holdings Inc. said Wednesday that it expects the frequency of workers compensation claims to continue declining this year while preliminary results show frequency falling 4% last year.

“While the overall decline is widespread and good news for workers, employers and their insurers, high-cost permanent total (disability) claims have emerged recently as a noticeable exception to this decline,” Boca Raton, Fla.-based NCCI said in a research brief.

The rise in permanent total disability claims appears to be driven primarily by workers age 50 and younger, NCCI said.

While it expects workers comp claims frequency to continue falling during a weak economy, NCCI said it is investigating why that age group’s permanent total disability claims are rising.

The report, “Workers Compensation Claim Frequency Continues its Decline in 2008,” is available at www.ncci.com.