God knows what got in the daily tracking polls today, because they’re all out of sorts.

Daily tracking polls update, 10/8: click to enlarge

Yesterday, the Diageo/Hotline poll suddenly had Obama’s lead drop by four points, from +6 to +2. That’s an unusually steep drop for a tracking poll. It was the biggest day-on-day change in any of the daily tracking polls since 7 September, over a month ago. It was all the stranger because none of the other tracking polls showed something similar: Obama’s lead dropped by one in the R2000/Kos poll, increased by a point in the Gallup poll, and was unchanged in Rasmussen’s.

Today, the weirdness continues. The Hotline poll has Obama’s lead down another point to +1. Rasmussen has his lead dropping by two points as well, from +8 to +6. But Gallup has it storming ever upward, today from +9 to +11; it has Obama at 52% of the vote. That result, as Gallup’s Jeff Jones points out, is “the best for Obama during the campaign, both in terms of his share of the vote and the size of his lead over McCain.”

So which is it? Is Obama up by 11%, 6% or 1%? That’s quite the difference. And is he moving up or down?

Well, on that count the balance doesn’t look as good as it has these past few weeks: the R2000/Kos poll also has his lead down a point, if still at a lofty ten points. That means his average lead in the four daily tracking polls has dropped from 8.5% to 7.0% in two days, when it hadn’t dropped by as much as a single point, even momentarily, at any point in the past month.

Do we reach for the panic button? Or even wonder what must have happened, exactly, in between Sunday and Tuesday? (Last night’s debate took place after all or the lion’s share of polling for today’s polls was done.)

Maybe not. The two-point Rasmussen drop is, Rasmussen’s own update underlines, nothing particularly significant:

The [..] Tracking Poll for Wednesday shows Barack Obama attracting 51% of the vote while John McCain earns 45%. For the past thirteen days, Obama’s support has ranged from 50% to 52% while McCain has been at 44% of 45% every day

Not so scary. So that really just leaves the Hotline poll. Versus the Gallup poll. Those polls, eh? With differences so big, can they be said to have any meaning at all?

Well, let’s not give up all too fast. For a week until yesterday, Rasmussen, Gallup and Diageo/Hotline were almost in exact agreement, showing Obama leads that were within at most two points from each other every day. For the nine days before that, none of them ever showed an Obama lead of more than four points more or less than any of the others. (The Research 2000/Kos poll is another matter – you have to subtract about three points from Obama’s lead in that one to get it in line with the other polls.)

So yes, obviously they are all out of whack today. And it’s easy to point and wonder, on a day like this, about just how random these poll numbers all seem to be, as Ezra Kleins briefly does with some wit. But on a day to day basis, those three tracking polls have shown pretty reliable trends, roughly consistent with each other. In fact, we have not seen the numbers for these three polls diverge this much at any time in the past month and a half. So it might be a tad unfair to pounce on today’s numbers and use them as a showcase about the unreliability of polls.

Presumably, one or two of them must have stumbled upon an unrepresentative sample for the day. Best to check them again in three days’ time, when they’re most likely back in tune with each other.

Then we’ll also know more about what, if any, effect last night’s debate has had. Obviously we can’t well use today’s numbers as basis for such a comparison, but we could use the ones from the day before yesterday and see how things will have evolved from there.

In the meantime, we’re just left to wonder: who’s got the unrepresentative sample? Gallup or Hotline? The state-level polls, per Nate Silver, are looking very good for Obama, in any case – check out those Pennsylvania and Wisconsin polls!