I've been tracking the favorability figures for the four candidates based on the numbers reported in the Daily Kos / Research 2000 polls, which have shown a sharp drop-off in favorability for both McCain and Palin over the last week. This seemed to be a clear trend, but when I look at other polls I am simply not seeing similar figures.
To take September 19th as an example, the R2000 poll shows 41% favorable, 46% unfavorable and 13% no opinion for Palin. But on the same date, the Diageo/Hotline poll shows figures of 50% favorable and 35% unfavorable (with presumably 15% undecided). This is a huge difference that cannot be accounted for by normal variations or differences in party ID splits. And while the Diageo/Hotline numbers are down from where they were a couple of weeks ago, they are up from earlier in the week.
The recent CBS / NY Times poll gave Palin 40% favorable and 30% unfavorable, with 15% undecided and 15% "haven't heard enough". The September 18th Pew poll likewise continues to show strong favorables for Palin.
The only reasonable conclusion I can come to is that the favorables numbers in the DK/R2K poll are messed up. This, combined with the obvious problems in their voter splits (too many Democrats, too many women and too many Hispanics, all of which help Obama) lends credence to the view that this poll, despite not being conducted by Daily Kos, is biased towards Obama.