The research program, IRS insiders say, is seen as an annoying necessity within the agency. When the tax collector began the program in 2001, it sent highly trained enforcement agents to examine close to 15,000 taxpayers each year. The depth of the study frustrated the agents, who were not recovering revenue, and members of Congress, who received complaints from constituents about the invasive nature of the program, according to a former top IRS official who spoke on the condition of anonymity to talk about sensitive internal discussions.