LOS ANGELES - A study from researchers at two elite universities attacking the notion that Internet file sharing is to be blamed for declining music sales has prompted the industry's trade association to issue a six-page response rebutting the study.

The Recording Industry Association of America issued its lengthy statement in response to a study released Monday called "The Effect of File Sharing on Record Sales: An Empirical Analysis," which was written by researchers at Harvard University and the University of North Carolina.

The study was heralded by those who share music files over the Internet as proof that their behavior should not be criminalized, and many Web sites friendly to peer-to-peer networks posted highlights of the study.

"While downloads occur on a vast scale, most users are likely individuals who would not have bought the album even in the absence of file sharing," the study asserts.

The 51-page study relies heavily on complicated mathematical formulas to conclude that file swapping has had an effect on music sales that is "statistically indistinguishable from zero."

The authors of the study - Felix Oberholzer, an associate professor at Harvard Business School, and Koleman Strumpf, an associate professor at UNC - said they tracked music downloads over a 17-week period in 2002 and compared them with sales patterns of 500 music albums (comprising CDs and cassettes) in order to conduct their research.

Even so, they got it wrong, the RIAA said Tuesday.

Their model, the RIAA wrote, "has no allowance for what people would have done if file sharing were not an available alternative."

The RIAA letter also calls Strumpf and Oberholzer's analysis "incomprehensible to the layman" and "inconsistent with virtually every other study done by academics and research analysts."

The RIAA backs its claim by citing more than a half-dozen competing studies.

According to the RIAA, the music industry has shrunk 31 percent since 1999 in terms of units shipped in all formats, and the trade association has maintained that the dramatic change is attributable to the illegal sharing of music online.