Applications for tax exemption from advocacy nonprofits had not yet spiked when the Internal Revenue Service began using what it admits was inappropriate scrutiny of conservative groups in 2010.

In fact, applications were declining, data show.

Top IRS officials have been saying that a "significant increase" in applications from advocacy groups seeking tax-exempt status spurred its Cincinnati office in 2010 to filter those requests by using such politically loaded phrases as "Tea Party," "patriots," and "9/12."

Both Steven Miller, the agency's acting commissioner until he stepped down Wednesday, and Lois Lerner, director of the agency's exempt-organization division, have said over the past week that IRS officials started the scrutiny after observing a surge in applications for status as 501(c)(4) "social welfare" groups. Both officials cited an increase from about 1,500 applications in 2010 and to nearly 3,500 in 2012. President Obama ask Mr. Miller to resign on Wednesday.

The scrutiny began, however, in March 2010, before an uptick could have been observed, according to data contained in the audit released Tuesday from the Treasury Department's inspector general for tax administration.