The poll that Kos is discussing is their “State of the Nation” poll — they needed a poll that happened every week to do the type of statistical analysis needed to catch R2000.
I hate to say this, but I recommend that freepers go through the Politico story (which is just some stupid politico “story” quoting the middle of the Markos explanation). You go to DailyKos, unfortunately, and then you have to link through to the report on the poll.
But when you do, it’s an interesting discussion of how you can tell if a poll isn’t really random samples.
I don’t give Kos credit — they have no choice but to distance themselves, as they were called out by others who did the research, and the story is pretty iron-clad.
http://www.fivethirtyeight.com/ did the research that KOS relied on I believe, to throw out Research 2k. Fivethirtyeight have some integrity and seem pretty professional