Respondents said other reasons for the tax gap are complexity of the tax law (28 percent), competitive pressures within certain industries (14 percent), and honest errors (1.3 percent).

CPAs believe small businesses and the self-employed are the most responsible for creating the tax gap (48 percent), followed by individuals (15 percent), and large companies (11 percent). Twenty-five percent said "other types of taxpayers" or "don't know."

The underreporting of income is the major component of the gap, said 55 percent of respondents. Other components include the overstatement of deductions (21 percent) and not filing returns (12 percent).

Interestingly, 49 percent of respondents identified the experience of a traumatic event in taxpayers' lives as the reason that taxpayers fail to file returns. One in three said taxpayers are primarily motivated to become compliant because of some recent IRS activity or publicity. One in five believe that a taxpayer remains a non-filer because the taxpayer starts believes that either he is not required to file or thinks he will never be caught.

The Internal Revenue Service earlier this year identified the $300 billion tax gap as its foremost problem. 

Debates and research on how to close the gap continue:

• The AICPA submitted comments to Congress opposing proposals made by the Joint Tax Committee that would expand the self-employment tax base as part of an effort to close the tax gap. "The tax gap is not closed one penny by expanding the tax base and tapping new sources of revenue," the AICPA said.
  
  
• Treasury Secretary Henry Paulson said that aggressive steps to collect taxes on underreported income would create a backlash from law-abiding taxpayers.
  
  
• In a Tax Talk Today Webcast, a panel of tax practitioners and officials discussed the federal government's latest efforts to improve voluntary compliance. Experts identified small-business noncompliance as a major tax-gap culprit.
  
  
• The IRS announced plans to launch a new National Research Program reporting compliance study for individual taxpayers that will provide updated and more accurate audit selection tools and support efforts to reduce the nation's tax gap.