Sorry to bring registration back into the Registration thread, but I thought an answer in another thread belonged here as well. Mostly, so it can be located next season when someone looks for it.
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86.8% of the 2010 rookies returned to play again in 2011. (37 of 281 did not return)
You need to compare that to the 2011 overall return rate of 91.5% (91.2% if you discount the rookies who did return) to make a valid comparison next year.
There are some historical numbers
here for how long teams last after their rookie year. It needs updating for this year and last.
A description of what the chart means is given by the author
here