The probe by the House Oversight and Government Reform Committee follows on from the launch of an inquiry by the Federal Communications Commission (FCC) last month.

Committee chairman Congressman Edolphus Towns has written to acting FCC chairman Michael Copps asking for an update on the status of the inquiry and how the commission plans to proceed.

Towns told Copps: “I remain deeply concerned that without deliberate and timely investigations into this matter the increased use of PPM will further threaten the financial viability of minority targeted radio stations.”

Broadcasters targeting ethnic minorities claim that the PPM system, which is being rolled out to replace the old diary-based method in major US radio markets, is undercounting their audiences because black and Hispanic listeners are not properly represented in the sample.

Arbitron has insisted that its system is reliable, arguing that differences between listening figures from the diary and PPM systems are due to the fact that PPM measures actual listening, while a diary-based system can only measure recall and loyalty.

However, the firm has previously acknowledged difficulties in recruiting ethnic minority panelists and ensuring they regularly carry their PPM device and, under pressure from clients, it has implemented a range of quality assurance improvements.

In his letter to Copps, Towns also notes the efforts made “to correct Arbitron’s methodological flaws in the implementation of PPM embodied in settlement agreements between the company and the states of New York, New Jersey, and Maryland”.

He concludes: “This is a very important issue with potentially far-reaching implications for the future of radio broadcasting, including the viability of minority-serving radio stations.”

Arbitron has issued a statement in response to Towns’ letter, welcoming “any opportunity to discuss the importance of electronic measurement, the effectiveness of the PPM technology, the value of the data it produces and our disciplined approach to the deployment of the service”.

CEO Michael Skarzynski said: “Arbitron looks forward to sharing with the Committee our expertise and insights based on our long history and extensive experience in gathering, distributing and supporting the currency that is used throughout the radio industry by broadcasters, advertisers and agencies.”