Oversight Committee chairman Edolphus Towns said analysis of the MRC documents also revealed Arbitron had made “insufficient effort” to use bilingual interviewers to recruit Spanish-speaking Hispanic sample participants, and that radio ratings are “almost consistently” based on data received from “an unacceptably low percentage” of sample audiences.

“These and other problems translate into a ratings disaster for minority-targeted radio stations,” said the congressman, who is leading an investigation into claims that the PPM system undercounts the audiences of black- and Hispanic-focused radio stations, thus harming their ad revenue.

In response, Arbitron said it was “extremely surprised and disappointed at the analysis and erroneous conclusions reached by the Oversight Committee staff”.

“We respect and support Chairman Towns’ commitment to the health of minority broadcasters and believe that our collaboration with his staff, the MRC, as well as a number of initiatives that we have under way, will help address that challenge,” the company said.

It added: “We look forward to a fact-based dialogue as we clarify some of the erroneous conclusions reached in this current analysis, and will continue to work to resolve these issues.”

So far, the PPM system has received MRC accreditation in only two markets – Houston and Riverside/San Bernardino.

Arbitron has previously acknowledged difficulties in recruiting ethnic minority panellists and ensuring they regularly carry their PPM device, though it has since made “methodological enhancements” to the ratings system designed to address these and other issues.

The firm has also previously stated that differences in listening figures produced by the PPM system and the paper diary method it replaces are due to the fact that PPM measures actual listening, while diaries only measure recall and loyalty.

Congressman Towns and the Oversight Committee kicked off their investigation in June. Towns later joined the House Judiciary Committee in pressing the Government Accountability Office to conduct a probe, though it has yet to respond to those requests. The Federal Communications Commission is also holding an enquiry.