Age and education do affect the vote. Many of 's wins have been fueled by big turnouts from younger voters, who have come out strongly for him. In many states, they also increased their share of the total votes cast.
For example, young voters made up 22 percent of the total vote in Iowa, up from 17 percent in 2004. They were 18 percent of the total in Georgia, up from 11 percent four years ago. Even in Ohio, a primary Obama lost to by ten points, the share of the vote cast by those under 30 rose from 9 percent to 16 percent.
Those are astonishing rises - especially since turnout in the primaries overall has also risen dramatically.
But Pennsylvania seemed to be an exception: the 12 percent of the vote cast by voters under the age of 30 was the same as their share of the Pennsylvania Democratic primary vote back in 1992, which is the last time the state had a meaningful Democratic primary. Obama's support among young Pennsylvania voters (60 percent) was a bit on the low side - it had been as high as 77 percent in Georgia and 76 percent in Virginia. And among white Pennsylvania voters under the age of 30, he did not even win a majority in Pennsylvania - according to the CBS News Exit Poll, 52 percent went for Clinton; 48 percent for Obama.
It's worth examining young voters by race and by education. In Ohio, Obama won 61 percent of the under-30 vote, but his margin over Clinton came almost entirely from young African-American voters. White Ohio voters 18-29 years old divided evenly, with 48 percent for each candidate.
Black voters accounted for a large share of the youth vote in other states, too. Half of the under-30 voters in Georgia were African-American, equal to the black share of the total vote there. In Ohio, they made up more than a third of the youth vote, much larger than their share of the total vote there. In Pennsylvania, the black share of the youth vote amounted to a little less than a third. But that was twice as high as the black percentage of the statewide vote, and much higher than the black share of the vote cast by those 60 and older n Pennsylvania: only about one in ten voters over the age of 60 there was black.
We know something about the role of education for young voters, too. CBS News worked with UWire - the news service for college journalists - to poll a representative sample of more than 2,000 Pennsylvania college students before that primary. Those who said they were registered Democratic voters in the state were overwhelmingly pro-Obama - 71 percent to 29 percent - and for that group, race mattered little. Whites favored Obama over Clinton 69 percent to 31 percent. Pro-Obama students were more enthusiastic than students supporting Clinton: six in ten liked him "a lot" better than Clinton; only 42 percent of Clinton's student supporters said they liked her "a lot" better than Obama.
But student opinion can be very different from the opinions of people who have left college - or perhaps have never gone. There are differences even within age groups depending on education.
In the last few days, reporters have asked Obama and his campaign managers if they thought the campaign might have problems attracting older voters. David Axelrod, Obama's senior political adviser, said: "I think there is a general inclination on the part of the older voters to vote for what is more familiar."
Obama himself told the press on Wednesday: "Our problem has less to do with white working-class voters. In fact the problem is that - to the extent that there is a problem - is that older voters are very loyal to Senator Clinton. And I think part of that is they've got a track record of voting for not just Sen. Clinton but also her husband."
Education is strongly related to social class. Looking at all the primary exit polls (combining exit polls, weighted to total votes, and excluding Florida and Michigan), it appears the "problem" the Obama campaign faces might involve both class and age. Among white voters with a college degree, Obama and Clinton have run almost even so far this year - 49 percent for Obama, 47 percent for Clinton. The results are very different by age within this group - those under 45 have given Obama a lead, and those over 45 have chosen Clinton. This does seem to support Obama's claim that older, better-educated Democratic voters are staying with what they know, keeping on "track."
White voters without a college degree, however, vote differently. This year, they have voted for Clinton over Obama by almost two-to-one - 61 percent to 33 percent. And the age of the voter matters less. Clinton leads decisively with just about all age groups of these voters - as long as they are over 30. She even edged Obama, 48 percent to 47 percent, among non-degreed voters under 30, but over 24 years old. Only the white non-college graduates younger than 25 have favored Obama so far this primary season. They voted for him 59 percent to 38 percent. This is the group that would include most of those pro-Obama undergraduate students.
We don't know exactly how large that group has been in the primaries this year - there is no exit poll question that measures students -- but the data suggest that any "problem" Obama has with older, working class white voters could start with voters a lot younger than we thought.
By Kathy Frankovic