Madden said no final decision had been made as to whether Romney would release his tax returns, but he did not release them during his 1994 run for the U.S. Senate or his 2002 run for governor.
The financial disclosure forms are designed to provide "protection against potential conflicts of interest," said Fred Wertheimer, president of Democracy 21, a nonpartisan group that promotes openness in government.
They are not, however, audited by the government, leaving the possibility of candidates filing incomplete or inaccurate documents.
In any event, the financial disclosure documents provide only a fraction of the information available on tax returns. They do not track charitable donations, gift-giving or stock transactions.
Candidates do not have to reveal the value of their mortgages, or deductions such as medical expenses, which can reveal chronic health conditions or ongoing medical treatments.
Only tax forms would reveal whether a wealthy candidate -- many of the 2008 candidates are multimillionaires -- have used loopholes to duck taxes.
And while candidates do have to describe their sources of income, they do so only in broad categories.
For instance, when Edwards revealed how much he was paid for his year-long stint consulting for the Fortress Investment Group, he can give a rough estimate -- between $50,001 and $100,000, or between $100,001 and $1 million, for example.
Joseph J. Thorndike, a historian and contributing editor for Tax Analysts, a nonpartisan group, acknowledged that privacy concerns may push candidates to keep their tax returns private.
But releasing one's forms, he said, demonstrates that a candidate "shows trust and respect for the office," he said.
In short, Thorndike said, the tax return tells "a lot about your life."
Jennifer Rubin is an independent writer and attorney living in Virginia.