BAGHDAD — While sophisticated roadside bombs have taken a heavy toll on American troops over the course of the war here, suicide bombings have largely been a hallmark of sectarian warfare. Independent researchers have now tried to quantify their damage, poring through data compiled from death reports to conclude that more than 12,000 Iraqis have been killed in at least 1,000 suicide attacks since the American-led invasion.

The paper is part of a series by the London-based medical journal The Lancet on the health consequences of the attacks on Sept. 11, 2001, which set off wars in Iraq and Afghanistan in which suicide bombings have become common, as they have in Pakistan.

The Lancet published studies in 2004 and 2006 that used samplings of casualties and statistical modeling to arrive at tolls of “excess” deaths (those that would not have happened without the war), which critics said were far too high. The paper released on Friday, however, relied on direct counts of deaths using information compiled by Iraq Body Count, an independent group that culls news reports and hospital and morgue records to try to keep track of civilian deaths.

Iraq’s ability to track the deaths is limited, and its record-keeping remains poor. The medical establishment is so diminished — many educated Iraqis have fled over the years — that the wounded are not always treated at a hospital, and the dead are quickly buried.