A new report released Tuesday by California-based Integrated Media Measurement (IMMI) shows that 20% of people are passing up the television to watch episodes of their favourite primetime shows online and that the largest portion are white, affluent, well-educated, working women aged 25-44.

‘This is the first study to show there are a significant amount of people watching primetime shows online who are not watching some portion of those shows on television,’ says Amanda Welsh, head of research for IMMI.

The study, which was executed through a research panel built by IMMI mirroring U.S. Census results for fundamental demographics in key markets, also showed that 50% of online viewers watch the programming as it becomes available, seemingly using their computers as an alternative to their TVs. The other half are using the Web as a means of catching episodes that they have missed or giving parts of episodes they have already watched another look.

Data accumulated by the study also indicated that in numerous cases, online viewing of a program was higher than DVR viewing of the same show. IMMI’s review focused on 14 primetime shows across two major American networks between the fall of 2007 and the spring of 2008.

The full report is available here.