It only makes sense that the first commercial in a cluster of TV commercials would get more viewership than the second or third or fourth, as people get up to go to the fridge or the bathroom.

But how much more? For the longest time there was really no way of knowing.

Now there is, and the hunch long held by media buyers is right on. That first commercial tends to get a lot more eyeballs.

This comes out of new data from Magna Global, the giant media buying agency, derived from second-by-second commercial ratings from TiVo, the DVR maker.

Commercials in the A position hold onto significantly more viewers from a program on network TV and cable TV than other commercials in a pod.

Based on programs recorded on a DVR and played back, commercials lose 59 percent of a network TV program’s rating. But commercials in that first slot lose only 49 percent. On the 10 largest cable networks, the overall commercial rating is 42 percent lower than a program rating, but only 29 percent lower for commercials in A position.

This new data, confirming what buyers long suspected, will surely have an impact on how advertisers buy TV ad time and the premiums they're willing to pay. Right now, most commercials are purchased on a rotation basis, meaning advertisers get whatever spot a network gives them within a commercial pod.

But it's not hard to imagine a marketplace in which placement within a pod will be negotiated, with advertisers willing to pay much higher rates for the A position.

Just when that might happen is hard to say.

The existing currency, Nielsen Media Research’s new average-commercial-minute ratings, don’t break out ratings for specific commercials. Also, the new data only reflects viewing in TiVo households, so it can't be applied to the entire TV-viewing universe measured by Nielsen.

But the TiVo data certainly indicates the value of pod placement and is likely to influence negotiations, particularly with DVR penetration now zooming past 20 percent.

“Nielsen can’t measure individual commercial ratings or pod positions,” says Steve Sternberg, executive vice president of audience analysis at Magna. “That’s one reason we need more granular measurement and why we are subscribing to TiVo data, to at least have some indication of what is going on and what might happen as DVR penetration grows.”

Nielsen’s average-commercial-minute ratings were used in upfront negotiations for the first time ever this summer.

TiVo began tracking second-by-second ratings on 20,000 of its DVRs last September. Magna’s parent company, Interpublic, and a handful of other agencies now subscribe to it as complement to the Nielsen data.

For this most recent study, Magna analyzed TiVo data from October through June.

Interesting, while it finds higher viewership for the A position in playback, it found that ads in that position in live viewing don’t do a whole lot better than other commercials within a pod. That's because in live viewing there's no opportunity to fast forward.

In fact, the ratings for all commercials on network TV dip 3 percent from program ratings on this measure, including those in the A position.

On cable TV, when programs are watched live, commercial ratings dip 4 percent below program ratings. Commercials in the A position do better, dipping only 1 percent.

Another finding is that broadcast and cable networks in particular tend to run a lot of promotional spots in the A position--12 percent for broadcast and more than 50 percent for cable.

That may change since the ratings are higher for the A position than other slots within a pod.

“Since promos are not counted in Nielsen’s average-commercial-minute ratings, I would guess that we’ll see more actual ads in A positions on cable networks as a way to improve reported ratings,” says Sternberg.