President Obama’s nominee to be the director of the U.S. Census Bureau, a former director of the Survey Research Center at the University of Michigan named Robert Groves, has not received a vote on his confirmation 40 days after the Senate Committee on Homeland Security and Governmental Affairs unanimously sent his nomination to the floor.

However, Groves’s confirmation by the full Senate has been stalled by at least one anonymous Republican senator. Under Senate rules, a Senator can hold up a nomination without going public or providing an explanation.

It has now been 40 days since Groves’s nomination hearing. One reason for the anonymous hold may be Groves’s support for statistical sampling. This practice is controversial because it involves using expert opinions to calculate the accuracy of figures rather than relying solely on a door-to-door headcount. As Time reported, when Groves was “an associate census director in the 1990s, [he] angered Republicans by supporting a statistical adjustment to compensate for the 1990 undercount.”

However, sampling should be a nonissue because the method was banned for decennial headcounts by the United States Supreme Court, and Groves has sworn not to use it for the 2010 Census.

Groves is one of 61 Obama nominees who are awaiting confirmation by the Senate.