There’s lots of data that the networks look at when deciding whether to renew or cancel a TV series but the ratings are the main ingredient. (Wonder if your favorite’s already been renewed or cancelled? Visit our NBC 2011-12 show page.

Which NBC shows are in danger of being cancelled or are hits? By looking at the chart below, you can see their current season ranking, ratings averages to date, and their letter grade in the all-important 18-49 demographic.

These charts incorporate final ratings data through Friday, June 1, 2012.

Summer 2012 ratings report card.

Original ratings data ©The Nielsen Company. All Rights Reserved.

A couple of notes about these charts:
The averages included in this chart are based on the final numbers, not the fast affiliate ratings that are typically reported the next morning. The final numbers become available about a day after the broadcasts or in some cases several days later. The charts will be updated as the new data becomes available.

Keep in mind that the demo numbers (not total viewers) are what’s most important to advertisers. Therefore, that’s how the networks measure success. Advertisers pay more for ad time on a show that has a higher demo rating versus one with a lot more overall viewers.

Demo numbers are reported by Nielsen using the 10ths decimal place (2.4, for example). We used to report averages that way but it ends up being hard to see any movement week to week. It can also be a little misleading since a show with a 2.35 average and a show with a 2.44 average will both round to a 2.4 rating.

In these charts, we’re including the demo average rounded to the 10th (2.4) as well as the 100th place (2.41) in parenthesis so you can get a better idea of how the average has been affected by the latest episode’s demo rating.

The letter grades are relative (kind of like grading on a curve) and are based on the individual network’s demo performance (either scripted or non-scripted). All of the networks have very different gauges for success right now. (A successful show for 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 different shows stand.

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

What do you think? Are surprised by any of the ratings? Are any of your favorite shows in danger of being cancelled? Which should be doing better?