Gallup's Frank Newport has posted an update
that responds to questions raised here
and elsewhere about the composition of those asked the Democratic primary vote
question in this week's USA
Today/Gallup poll. The key
There has thus been no change in
this methodology which would account for Obama's gain against Clinton in this latest poll. More
importantly, a careful analysis of the data shows that there has also been no
significant change this year across 9 polls in the percent of the overall
Democratic sample who are Independents leaning Democrat compared to the percent
who are "pure" Democrats...
In other words, there were just as
many independents in the previous samples showing Hillary Clinton with a
healthy lead over Obama as they are in the latest sample showing Clinton and Obama tied. So
an argument that some change in the sample composition (as defined by these
political measures) accounted for the shift in voter preference is not
supported by the data.
also provided me with the data he references above. As Pollster readers might
be interested, I have reproduced it here (omitting results for candidates other
than Clinton and Obama):
data supports his contention. Independents that lean Democratic were 35% of the
subgroup that answered the Democratic primary horse-race question. That is
exactly the same percentage as the Democratic leaner composition I get when I
average all the nine surveys.
Of course a bigger question is whether a national survey on
the Democratic primary contest should include that many independent
identifiers. On this score, Gallup
is not alone. Most of the other national surveys do the same (though some,
include only registered voters).
This is a tough issue to resolve since the notion of a
national "likely Democratic primary voter" is so abstract to begin with. We do
not have a national primary, of course, and the rules for participation and
turnout levels vary so wildly across states that it is next to impossible to
try to use a national survey of this sort to model the entire nation.
However, we might suggest that all national pollsters begin
regularly reporting both their sample composition (% of independent leaners) as
well as the results among pure Democratic identifiers. The more we know, the
more we know.