WASHINGTON  Of nearly 2.2 million immigrants deported in the decade ended 2007, more than 100,000 were the parents of children who, having been born in the United States, were American citizens, according to a report issued Friday by the Department of Homeland Security.

But the department lacks data that might have addressed questions left unanswered by the report, like the number of American children who were left behind in the United States or, alternatively, exited the country with their deported parents. Nor could the report say in how many instances both parents of such children were deported.

Similarly, said Representative José E. Serrano, Democrat of New York, since no one knows how many children a given deportee had, the number of affected children could be much higher than 108,434, the exact number of deported parents of American citizens.

So “the problem goes deeper than just the numbers you see,” said Mr. Serrano, who requested the study. He called the circumstance “tragic.”