It’s only the third week of the broadcast season, but based on the performance of new and returning shows CBS and Fox look to be doing the best of the broadcast networks, and the CW is doing fairly well. But ABC and NBC are hurting.

That's according to an analysis of Nielsen ratings for the new season by Magna, the media buying shop.

CBS in particular is seeing many of its returning shows post ratings increases from last season, and an encouraging sign is that its new “The Mentalist” pulled about the same rating in its second week as it had for its premiere.

Going into the season many media people had predicted that ABC and Fox would have a strong fourth quarter while NBC and the CW would struggle. CBS's strong start stands out as the surprise.

“It’s too early to make broad statements but it certainly is a positive indicator if a returning show is starting out as well as it did last year,” says Steve Sternberg, executive vice president of audience analysis at Magna. “It looks like CBS and Fox are in pretty good shape right now.”

Among the returning CBS shows posting ratings increases are “Criminal Minds,” “CSI: Miami,” “CSI: NY,” “NCIS,” the Monday sitcoms “How I Met Your Mother” and “Two and a Half Men” and the newsmagazine “48 Hours Mystery.”

While its “Big Bang Theory” and “Survivor” have posted year-to-year declines, they are minimal, according to Magna.

Giving Fox its strong start are returning shows like the “Simpsons” and other Sunday sitcoms and the drama “Bones.” All have shown improvement over last season, and its new drama, “Fringe,” was up last week over the prior week.

The problem for Fox is that a few of its shows are losing viewers as the season goes on, including its new game show, “Hole in the Wall,” while the sitcom “Do Not Disturb” has been canceled.

By contrast, ABC and NBC are seeing many of their returning shows posting declines, and their new shows are not doing all that well, according to Magna. Notable decliners include ABC’s “Private Practice” and NBC’s “Heroes.”

What's boosting the CW is a solid increase in ratings for the returning “Gossip Girl” and a slight increase for “Supernatural,” while “America’s Next Top Model” and “Smallville” have posted modest declines.

Sternberg points out that the performance of returning shows is more indicative of how each network will do for the full season than the ratings performance for new shows, and that's simply because there are more returning shows.

“Returning shows naturally decline over time, so it’s important to have new shows to freshen the lineup,” says Sternberg. “But a network is going to go up or down in the standings mostly because of returning shows. One new show isn’t going to boost an entire night, outside the occasional blockbuster.”