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Welcome to our Ratings Survival Guide, a handy new feature which takes each new fall series on the broadcast networks and tells you the numbers it will need to survive for a second season. In general, a show's success isn't so much where it lands on the weekly ratings chart but rather how it performs in two key categories:

1. How much of its lead-in audience it retains. If a show averages 10 million viewers that's a good thing. But if the show that airs before it is averaging 30 million viewers, that's not a good thing. Why? Because 20 of those 30 million viewers decided to turn off that particular channel when the next show came on.

2. How it performs year-to-year in its time period. A new show is usually in its time period because the network thinks it can do better than it did in that slot last year. In other words, do worse than the show that was canceled after three weeks last fall then you too probably are not long for this world.

As you'll see, together these measurements paint a clear picture on how a particular show is doing. So without further ado, let's begin.

BLEEP MY DAD SAYS (CBS)
(Thursdays at 8:30/7:30c)

If any series can replace "Survivor" on Thursday nights it's "The Big Bang Theory" (14.13 million viewers, 5.22 adults 18-49 rating on Mondays last season). Said move will certainly give newcomer "Dad" a significant platform, although it's unclear what the expectation is in terms of retention rate. "Big Bang" obviously built off its "Two and a Half Men" lead-in while shows like "Rules of Engagement" (83%) and "Worst Week" (62%) previously followed "Men" to varying results. Presumably, "Dad" will have to perform in the 70-75% range or risk cancellation. Still, keep in mind that in the past two years, "Rules's" third season had the lowest retention rate of any comedy that was renewed (the aforementioned 83%).

Here's how CBS has fared on Thursday nights the past two seasons (viewers are in millions, adults 18-49 is the percentage of said viewers in the demographic; all are based on fast national data, using only first-run episodes):

thursdays in 2008-2010	time	viewers (retention)	adults 18-49 (retention)
CSI: Season 9	9:00 PM	17.75 (145.13%)	4.71 (124.27%)
Survivor: Season 17	8:00 PM	12.50 (N/A)	4.03 (N/A)
Survivor: Season 18	8:00 PM	12.10 (N/A)	3.86 (N/A)
Survivor: Season 20	8:00 PM	12.33 (N/A)	3.83 (N/A)
Survivor: Season 19	8:00 PM	12.23 (N/A)	3.74 (N/A)
CSI: Season 10**	9:00 PM	14.88 (127.64%)	3.43 (99.42%)
The Mentalist: Season 2**	10:00 PM	15.15 (103.59%)	3.39 (99.12%)
Eleventh Hour	10:00 PM	11.66 (62.86%)	3.06 (60.24%)
Harper's Island	10:00 PM	8.33 (53.29%)	2.37 (64.05%)

** includes only first-run, in-season airings in the specified time period

COMING TOMORROW: CBS's "Blue Bloods" and FOX's "The Good Guys."