Even as the number of workers compensation claims declines, the number of questionable claims is increasing, according to an analysis by the National Insurance Crime Bureau.

The study examining the 2011-2013 period, found medical loss claims were the largest source of questionable claims.

In 2011, 3,349,925 workers comp claims were found in the Insurance Services Office (ISO) ClaimSearch database, the report said. That number decreased to 3,244,679 in 2012 and is on track to decrease again in 2013 based on the 1,498,725 claims received in the first half of 2013.

But questionable claims are not following the same downward trend. In 2011, 3,474 questionable workers comp claims were referred to NICB. That number increased to 4,460 in 2012 — a 28 percent rise, the report said. Questionable workers comp claims accounted for 3.5 percent of the total 100,201 questionable claims submitted in 2011 and increased to 3.8 percent of the 116,171 total claims in 2012.

Through the first half of 2013, 2,325 questionable workers comp claims have been referred to NICB (3.7 percent of 62,352 total claims), compared with 1,681 through the first half of 2011 and 2,174 through the first half of 2013.

Questionable medical workers comp claims constitute 62 percent of the questionable claims; liability claims were the second most common, 37 percent of the total, the analysis determined.

Most questionable claims in 2013 were from California and Los Angeles was the city with the most questionable claims. California ranked first generating a total of 2,270 questionable workers comp claims, the report said. Illinois was next with 689 and New York was third with 688.

When ranking states per 100,000 residents, Delaware ranked first in 2011, Connecticut ranked first in 2012, and Maine ranked first in the first half of 2013.