It's more difficult than ever to predict which TV shows will be renewed come spring and which will be canceled.

With ratings down across the board, that measurement tool is no longer a primary factor in network executives' decisions. Now the decision just as often can come down to production cost, DVD sales, streaming volume and whether or not a network owns a stake in a series.

Regardless of Hollywood vagaries, the Post-Gazette's annual Keep or Cancel? poll once again offers viewers an opportunity to weigh in.

One vote per computer will be accepted. Series receiving an inordinate, unbelievable number of votes will be disqualified. If you don't own a computer or more than one person in your household wants to vote, you can write to me -- no phone calls or e-mails accepted -- with your choices, age, gender and ZIP code. One ballot will be cast per envelope received.

Votes will be tallied through April 25, and shortly thereafter the results will be published in a Friday Tuned In column. We'll send the results to each broadcast network president before the week of May 16, when the networks announce their new fall schedules.

If you want to advocate for a specific series in a letter, we've included network addresses, which are always available at www.post-gazette.com/tv under "TV Links" in the gray box on the right side of the page.

Here's where some of the most vulnerable series stand as of early March:

"Better Off Ted" is dead and "Scrubs" is out, too. The network already announced that "Ugly Betty" will come to an end.

Beyond that, much of ABC's schedule is on the bubble.

"FlashForward" and "V" won't return until later this month, but if I had to guess, I think "V" stands a stronger chance of continuing in the 2010-11 TV season.

Viewers seem to have forgotten about "The Forgotten," so it's unlikely to be back. Ditto for "The Deep End."

The network already announced renewals for "The Middle," "Modern Family" and "Cougar Town." "Castle" seems like a shoe-in for renewal given its ratings gains this season.

"Cold Case" barely got renewed for this season and its ratings have fallen further; it's likely to be cold-as-a-corpse come May. "NUMB3RS" is also liable to face the axe.

"Accidentally on Purpose" appears to be a longer shot for renewal than Wednesday night comedies "New Adventures of Old Christine" or "Gary Unmarried," but neither of these is a lock to return either.

Ratings this month for "Rules of Engagement" may determine its fate.

"The Vampire Diaries," "Gossip Girl," "90210," "Supernatural" and "America's Next Top Model" will be back and "Smallville" seems likely to return.

"One Tree Hill" is on the bubble along with "Life Unexpected." A "for rent" sign is sure to appear in the time slot for the new "Melrose Place," which will be condemned for lack of viewer interest.

"The Cleveland Show" and other animated series have already gotten 2010-11 pickups. "Glee" and "House" will be back along with "Bones." "Fringe" is likely to continue.

The big questions are whether "Lie to Me," currently on hiatus, will return, and whether Jack Bauer (Kiefer Sutherland) gets another day on the increasingly unwatchable "24."

With so many holes in its schedule (thank you, "The Jay Leno Show"!), NBC seems best positioned to renew a raft of low-rated series, which could include "Mercy" and "Community." "Trauma," though less likely, could also have a shot. "Chuck," "Law & Order" and "Law & Order: SVU" seem likely to be back.

"Heroes" is also on the bubble and although its cast members think it will return, it does not deserve that favor.

TV columnist Rob Owen's Tuned In+ is featured exclusively on PG+, a members-only web site from the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.