Nielsen Media Research warned clients in an electronic mail message delivered June 10 and obtained by Advertising Age that the number of reporting diary households for the period was "lower than anticipated" in the majority of local markets processed to date.
Nielsen said it is investigating the reasons for the poor response rates, but added it "has concluded that the reported data are projectable, and that there is no increase in the bias of the reported audience estimates."
The e-mail stirred up heated responses from the networks and ad agencies that rely on Nielsen data from the November, February and May sweeps to determine ad rates in local markets.
David Poltrack, exec VP-research and planning for CBS-TV, lashed out at Nielsen's diary system, calling it "dysfunctional" and saying it yields "unacceptably low, and declining, cooperation levels, [and is] administered by a part-time staff that's an embarrassment to Nielsen, the TV industry and advertisers."
Mr. Poltrack said that in one market, Miami, "the response rate was only 18%."
Allen Banks, exec VP-North American media director at Saatchi & Saatchi, and chairman of the media policy committee of the American Association of Advertising Agencies, said Nielsen's insistence that the May data "are projectable" is "nonsense."
"The diary system during the sweeps is almost bankrupt, and its results, at best, questionable," Mr. Banks said. "It troubles me greatly. I just hope that enough people in our industry get angry about the situation that some constructive improvement can occur."
The Four A's and Association of National Advertisers have already spoken out against the current sweeps system; among fixes proposed is a plan to increase the number of weeks measured, which would make local stations less likely to rely on programming stunts to artificially boost ratings.
"But any plan such as that is separate from the response rate problem Nielsen has," Mr. Poltrack noted.
He said that in the 26 metered markets where diary data from May have been tabulated to date, the average response rate was 30%, down from 33% last May.
"It's down in 25 of the 26 markets," Mr. Poltrack said.
"Overall, the diaries are a very affordable way to do local measurement," said Jack Loftus, Nielsen's VP-communications, adding, "You can't force people to cooperate."
He conceded that in May Nielsen missed its target cooperation rate by 6%, but he quickly added, "If you look back over the last three years, which is 12 reporting cycles, we actually did better than our target rate in every one but May."
Nick Schiavone, senior VP-research at NBC, said that Nielsen needs to focus itself: "But what is not clear is how many [problems] they can resolve at once."