An in-depth study into music libraries held by both illegal file-sharers and non-sharing peers has found that those who download copyrighted material for free are also likely to buy more content online.

It has long been argued by organisations such as the Recording Industry Association of America (RIAA) that illegal file-sharing deprives artists and the entire supply chain of revenues amounting to billions of dollars.

"While downloading one song may not feel that serious a crime, the accumulative impact of millions of songs downloaded illegally – and without any compensation to all the people who helped to create that song and bring it to fans – is devastating,"  RIAA says.

The association also claims that the illegal file-sharing network is responsible for 70,000 lost jobs and $2 billion in lost wages to American workers.

However, a study by the American Assembly, a public policy forum affiliated with Columbia University in the US, shows that those amassing large music libraries by obtaining that material in breach of copyright are also buying around 30 per cent more music legally than conventional consumers.

In addition, in the US at least, the study found that almost as much content was ripped from CDs owned by friends and family as was illegally downloaded online.

The "Copy Culture in the US and Germany" poll was made by calling thousands of North American and German citizens and interviewing them about their music collections.

"US P2P users have larger collections than non-P2P users (roughly 37 per cent more)," said the American Assembly's Joe Karaganis. "And predictably, most of the difference comes from higher levels of ‘downloading for free’ and ‘copying from friends/family'.

"But some of it also comes from significantly higher legal purchases of digital music than their non-P2P using peers – around 30 per cent higher among US P2P users. Our data is quite clear on this point and lines up with numerous other studies: The biggest music pirates are also the biggest spenders on recorded music."

The full report is expected to be published soon.