Among 395 likely Democratic caucus goers, Sen. Barack Obama leads Sen. Hillary Clinton by a statistically insignificant margin (35% to 29%) in a national primary; former Sen. John Edwards receives 18% and Gov. Bill Richardson 12%.
Among 275 likely Republican caucus goers former Gov. Mike Huckabee leads former Gov. Mitt Romney (39% to 17%); Sen. Fred Thompson receives 10%, former Mayor Rudy Giuliani 9%, Rep. Ron Paul 8% and Sen. John McCain 6%.
All other candidates receive less than five percent.
From the Newsweek release: "Likely Republican caucus-goers are 16% of all Iowa adults 18+ (weighted cases). Likely Democratic caucus-goers are 24% of all Iowa adults 18+ (weighted cases)."
Compare to comparable statistics for the October Des Moines Register poll (12% and 10% respectively) as well as the actual turnout for the 2004 Democratic caucuses (5.5%) and the Republican caucuses in 2000 (3.9%) and 1988 (5.3%).
Update: Several commenters question whether the six-point Obama lead could possibly be statistically "insignificant." I used that word above to paraphrase the conclusion from the Newsweek article:
While the Illinois senator's lead among Democratic caucus-goers in this poll is not large enough to be statistically significant, things seem to be trending his way, Hugick said.
Hugick's calculation is correct. For this sample of 395 likely caucus goers, a six point margin is not large enough to be "statistically significant" assuming the commonly accepted 95% level of confidence. Remember, the margin of sampling error (+/- 6% in this case) applies to the percentage for each candidate separately, not to the margin between candidates.
While the Obama lead is not "significant" at a 95% level of confidence, it would be significant if we were willing to relax our level of confidence to about 85%. See Gary Langer's column from earlier this week for more detail on this issue.