Found a DOT audit of DPE checkrides while researching something else. Had this paragraph:
To determine the impact of an inspector observing the test, we analyzed information obtained from PTRS reports and supplemental information provided by the FSDOs, such as whether an applicant was on-board when the DPE was tested and the results of the test. At three of the four FSDOs visited, 70 percent of the applicants tested (33 out of 47) passed when inspectors observed the tests. In comparison, the overall pass rate for DPEs at the four FSDOs was 90 percent in FYs 1994 and 1995. This significant difference in pass rates suggests DPE testing procedures may be more stringent when observed by an inspector. In addition, the lower pass rate demonstrated FAA's preferred method of surveillance, observing a DPE administer a test to an actual applicant, was a more effective surveillance method to ensure DPEs certify only qualified pilots.As if we didn't suspect.