WASHINGTON (AP) — An analysis of state and federal data suggests that cellphone use by drivers involved in fatal crashes is seriously underreported.

The National Safety Council, an advocacy group, said the underreporting makes the distracted-driving problem appear less significant than it actually is, and impedes efforts to win passage of tougher laws.

The council reviewed 180 fatal crashes from 2009 to 2011 in which there was strong evidence the driver had been using a cellphone. But only half the 2011 crashes were coded in the National Highway Traffic Safety Administration's accident database as involving cellphone use. In 2009, 8 percent of the crashes examined were coded as involving cellphones. In 2010 the figure was 35 percent.

The study was paid for in part by Nationwide Mutual Insurance Company.