There’s lots of information that the networks take into consideration when cancelling or renewing a TV series but the ratings are the biggest factor, particularly the 18-49 demographic. That’s the group that the advertisers want to reach the most so the networks must cater to them.

Viewership is obviously lower during the summer months (here’s the ABC report card for the regular 2011-12 season).

The following chart incorporates final “Summer” season ratings data through Thursday, September 6, 2012.

Original ratings data ©The Nielsen Company. All rights reserved.

Other summer ratings report cards: CBS | The CW | FOX | NBC

A couple of things to remember:
The averages included in these charts are based on the final numbers, not the fast affiliate ratings that are reported the morning after a show airs. These final numbers become available one to three days later (depending on holidays or weekends).

Demo numbers are reported by Nielsen using the 10th decimal place (2.1, for example). In these charts, we’re including the rounded demo average as well as the average in 100ths (2.14, for example) in parenthesis so you can get a better idea of how the number’s been affected by the latest episode’s rating.

The letter grades are relative and are based on the individual network’s overall performance in either the scripted or non-scripted categories. The networks all have very different gauges for success. A hit show on The CW would get quickly cancelled on CBS. Our system for coming up with letter grades isn’t perfect but it should still give you an idea of where the shows stand when compared to others on the same network.

*The letter grades for TV series that run on Friday and Saturday nights are weighted a little differently to compensate for them airing on little-watched nights.

What do you think? How are your favorites doing? Which ones would you like to see cancelled or renewed?