Gallup Guru Frank Newport followed up on the discussion here
and elsewhere about "possible differences between broad samples of voters and
likely voters" when Gallup
asks about the 2008 party nomination contests on national surveys. His conclusion:
[O]ur analysis suggests at this point there is
little difference at the national level in candidate preferences even when we
analyze smaller groups of more hard-core voters. For our latest national poll,
we narrowed the sample down to those Democrats who said they were "extremely
likely" to vote in the Democratic primary in their state next year. No
difference. Hillary Clinton heads by 20 points over Obama. We also looked at
"pure Democrats" -- excluding those independents who lean Democratic. Hillary
does even better among her party faithful, beating Obama by 30 points.[snip]
What about likely voters on the
Republican side? Fred Thompson picks up a little among Republicans who are
extremely likely to vote in the Republican primary, such that Giuliani's lead
is trimmed to 8- points, 32% to 24%. Among hard-core Republicans -- excluding
independents who lean Republican -- Giuliani is ahead of Thompson 30% to 20%.Bottom line: The basic structure of
the national presidential race for both parties appears to be similar
regardless of whether one looks at all voters, or just those voters who are
most likely to actually vote.
A further analysis of the same data
posted this morning by Gallup's Lydia Saad provides
more numbers for the Democrats, plus more information on the subgroups that Newport examined. First,
for the Democrats:
- AllDemocratic identifiers and "leaners" (initially independent adults thatsay they lean to the Democratic Party) - 48% of adults.
- AllDemocratic identifiers and "leaners" that also say they are "extremelylikely" to vote in the Democratic primaries or caucuses" - 27% of adults; 58% of allDemocrats & leaners.
- "PureDemocrats" (excludes independent "leaners") - 30% of adults.
- Pure Democratsthat are registered to vote plus registered Democratic "leaners" that saythey are "extremely likely" to participate in the Democratic primaries orcaucuses - 30% of adults; 63%of all Democrats & leaners.**
The table below shows the full results included in the Saad
report for the first and last groups, plus the Clinton
margins reported in Newport's
Gallup Guru post. As Saad notes, looking at the last group (registered
Democratic identifiers plus "extremely likely" registered leaners):
Clinton still dominates the field, although
by a bit smaller margin than among all Democrats. Support for Clinton remains about the same, at 47%, but
the percentage choosing Obama is slightly higher, at 31%.
One take-away point from these data. How the pollster defines a "likely voter" matters as much as how tightly they screen. Notice that the third and fourth columns above capture slices of Democrats that are the same size (30% of adults) but with very different compositions. Clinton leads Obama by 30 points among "pure Democrats," but remove non-registrants and add back indpendents that are "extremely likely" to vote in a Democratic primary, and Clinton's lead drops to just 16 points.
Also, bear in mind that the actual turnout in all of the 2004 Democratic primaries and caucuses amounted to less than 10% of adults in the United States.
**The definition of the fourth subgroup in the Gallup report is a bit ambiguous.
I emailed Gallup
to request confirmation.