The media research agency operates strict rules to prevent stations learning the identities of respondents, and will go so far as to delist any station that tries to make contact with panellists.

In a memo issued this week, Arbitron urged stations to let the agency know if any respondent tries to contact them direct via sites like Twitter or Facebook. Clients were also told to remind staff that rules on communicating with panellists, or attempting to communicate with them, apply to social media in the same way that they do to on-air comments.

Nielsen has similar rules in place to protect its TV ratings. Last year it slapped the wrists of talk show queen Oprah Winfrey when she tweeted her nine million followers to ask them to tune in to her new show “especially if you have a Nielsen box”. Winfrey later removed the tweet and apologised.