Record sales in the US have fallen because of people using the internet to download albums, a study suggests.
The students' spending habits fell when they could download albums
The report, for the country's National Bureau of Economic Research, studied the habits of 412 students.
It said the US music industry lost one fifth of a sale for each album downloaded from the internet.
The study contradicts a previous report, conducted in 2002, which said swapping songs online had no negative effect on music sales.
That report, by Harvard and North Carolina universities, said high levels of file-swapping had an effect that was "indistinguishable from zero".
Other research quoted by the IFPI global music industry body has estimated some 15% of users who download music illegally go on to spend more on music.
But the IFPI added that for every one person who uses file-sharing networks to sample music, a further two will cut back on their purchasing, or stop buying music altogether.
The report, Piracy on the High Cs, was compiled by University of Pennsylvania professors Rafael Rob and Joel Waldfogel.
It asked the students about the albums they bought and those they downloaded without paying.
The Red Hot Chili Peppers' albums were highly valued by the students
The students obtained 1,209 albums when downloading was available.
They purchased 617, while a further 592 were downloaded.
But if downloading was not available, the 617 albums would still be purchased, along with a further 154 which would have been downloaded.
It also said each student's spending on music declined from $126 to $100 when downloading was taken into account.
The report asked the students to put a value on the music they had bought or downloaded over time.
Nearly a third of the sample who had albums by the Red Hot Chili Peppers said it grew more valuable to them as time went on.
But over 80% of Britney Spears album owners said they had grown tired of her records.
Albums bought legitimately were valued more than downloaded music, the study said.