Nielsen is rolling out a TV rating service blending traditional television ratings with measures for online TV show viewing, reports Variety. The firm’s Extended Screen service will provide a single rating blending the two measurements, with data collected from meters placed in 7,500 households representing about 20,000 people. Under pressure to do so by network advertisers, Nielsen had launched a service measuring online video and installed meters in those households last month. In what Variety calls a wrinkle in the Extended Screen service, Nielsen is only collecting online data from internet versions of TV shows that have the exact same ads as their original broadcast. The criteria eliminates the most popular online destinations for internet TV including Hulu and the TV networks own web sites. Variety points to cable-provided online video services such as Comcast’s Xfinity and Time Warner’s TV Everywhere as places where some streamed shows retain their full ad load, making them eligible for Nielsen tracking. Nielsen said the first set of Extended Screen data will be available at the end of the year, although the firm will consider it evaluation data until they become part of its national ratings in February 2011. Read more at Variety.