The Readership Institute released a study, including 100 US newspaper markets, to tally Reader Behaviour Scores between 2000-2008.

Use of newspaper web sites was measured using a self-reported metric called SUM (Site Usage Measure). Individual online "experiences" with newspaper sites were analyzed. Web newspaper consumption and a newspaper site's social involvement were also studied.

For more details, here is the PDF document.

Source: Readership.org throough IFRA Executive News Service