Americans lost about $49.3 billion in 2006 to criminals who stole their identities, an 11.5 percent decline that may reflect increased vigilance among consumers and businesses, a study released on Thursday shows.

Losses declined from a revised $55.7 billion in 2005, according to the third annual study by Javelin Strategy & Research. They had increased in each of the prior two years.

The average identity theft fraud fell 9 percent to $5,720 from $6,278, while the median — where half were larger and half were smaller — held steady at $750.

“Businesses are doing a better job screening, and consumers are doing better at locking up information and monitoring their accounts,” said James Van Dyke, founder and president of Pleasanton, California-based Javelin, in an interview.

“The dollar amount is dropping,” he added, “but $49 billion is still a lot of money.”