NOTE: As a Media Matters commenter pointed out, Olbermann provided the following explanation on the weblog Firedoglake for why he has not been a host or guest during MSNBC's special election coverage:

I'm co-anchoring the election with [Chris] Matthews Tuesday night. And MSNBC has asked me to do whatever I could during these “politics days” -- but a) I have my daily radio commitment, and b) I don't want to diminish Countdown by not being around to write it.

As MSNBC's October 27 press release on the network's Decision 2006: Battleground America noted, starting October 30, MSNBC has been “devoting all of its daytime programming to politics,” with coverage of the midterm elections slated to air “through Election Day ... with MSNBC Election Anchor and 'Hardball' Host Chris Matthews anchoring, along with MSNBC's Keith Olbermann, Joe Scarborough, Tucker Carlson, Norah O'Donnell and others.” But a Media Matters for America review of MSNBC's daytime Battleground America coverage found that while prime-time anchors Matthews, Scarborough, and Carlson have all participated in MSNBC's special midterm election coverage, Olbermann has been absent.

The review found that Matthews, Scarborough, and Carlson have either hosted or contributed to 19 different segments in the special combined, whereas Olbermann has not appeared in any of MSNBC's election coverage, outside of his own program, Countdown. Only during the November 4 edition of Battleground America did MSNBC air a segment featuring Olbermann, but it was a clip from Countdown, not a personal appearance.

Carlson, Matthews, and Scarborough anchor MSNBC's Tucker, at 4 and 6 p.m. ET on weekdays, Hardball with Chris Matthews, at 5 and 7 p.m. ET on weekdays, and Scarborough Country, at 9 p.m. ET on weekdays, respectively. Countdown with Keith Olbermann airs at 8 p.m. ET on weekdays.

Media Matters has documented numerous instances of conservative information in MSNBC's recent election coverage. For instance, the October 24 edition of Decision 2006: Battleground America -- The Homestretch, which appeared to be a preview of MSNBC's special election coverage, was rife with conservative misinformation, Republican talking points, and falsehoods. Since October 30, MSNBC's weeklong Battleground America coverage has been marked by various MSNBC hosts, correspondents, and analysts uncritically reporting smears against Democrats; declaring a Senate race in which the Democrat leads by 13 points “tight,” while declaring a Senate race in which the Republican leads by 12 “all but over;” failing to note falsehoods in Republican campaign advertisements attacking Democrats; failing to challenge conservatives' baseless attacks on Democrats; and attacking Sen. John Kerry (D-MA) over a self-described “botched joke” he made during a California campaign appearance (here, here, and here).