Bounce? What bounce?

This USA Today/CNN/Gallup poll has some interesting data from before and after the Democratic convention. The numbers are still too close to call and within the margin of error, but the movement is surprising.

During the Democratic convention, among likely voters, the number of certain Bush voters increased by 5% while overall Bush voters increased by 3%; Kerry's numbers declined a bit.

[See UPDATE III below. USA Today has pulled the likely voter data from its site!]

Here are the data:

BEFORE CONVENTION (Jul 19-21):

• Kerry/Edwards 49% (43% certain, 6% leaning)
• Bush/Cheney 47% (40% certain, 7% leaning)

AFTER CONVENTION (Jul 30-31):

• Kerry/Edwards 47% (42% certain, 5% leaning)
• Bush/Cheney 50% (45% certain, 5% leaning)

UPDATE I: Others caution against reading too much into these numbers.


UPDATE II: Newsweek's poll gives Kerry a small bounce:

Kerry’s four-point “bounce” is the smallest in the history of the NEWSWEEK poll.

Newsweek blames, in part, the media:

And limited coverage by the three major networks also may have hurt Kerry.

UPDATE III: USA Today has pulled the likely voter numbers from its site as of this posting (10:10 pm EST, Aug. 2, 2004). Left on the site are the less relevant, but more favorable to Kerry, numbers for national adults and for registered voters. Does anyone have an explanation?