Advertising agencies are asking Nielsen Media Research to drop VCR recordings from the average commercial ratings it plans to calculate next season.

All shows recorded by VCRs have been included in program ratings because Nielsen has been unable to come up with a way to accurately measure VCR playback. Since some shows recorded are never watched, and many of the commercials in those shows are fast-forwarded, including them in the ratings has long angered ad buyers. In the recent upfront, ad buyers excluded from their negotiations with the networks shows watched on a delayed basis on digital video recorders.

In a letter sent Thursday to Nielsen President Susan Whiting, the American Association of Advertising Agencies said “The network argument that since Nielsen can’t measure VCR playback, it is equally unfair to remove recording from the ratings as leaving it in … no longer holds up” when talking about commercial measurement. The group said it would not be helpful “for a commercial minute [data] tape to be released containing VCR recording, unless playback can be accurately measured by you.”

David Poltrack, chief research officer at CBS Corp., said the network agreed that measurement should be based on VCR playback, but since that can’t be measured, recording should be included in the ratings because most of it is played back.

VCR usage is declining, Mr. Poltrack said. In prime time, it accounted for 4.6 percent of viewing in May, down from 5.2 percent in May 2001. VCR penetration was 90 percent in 2003 and has dropped to 83 percent currently.

“With all the measurement challenges that we have, we don’t think it’s in the best interest of the industry to spend a significant amount of money to measure something that’s going away,” he said.

The Four As letter also expressed concern about the way commercial minutes are defined, how commercial minutes on cable are calculated and on whether Nielsen’s Monitor-Plus service, which contributes data to the commercial ratings, should require accreditation from the Media Research Council.

Nielsen had no comment yet because it had only just recently received the letter, a spokesperson said.