Updated to include today's Suffolk poll release: Depending on which age distribution you use for the Suffolk poll, Romney's lead goes from 20.4% (averaged Suffolk) to just 18.2% (Marist) over Ron Paul. Also, Huntsman drops 0.1 (Avg Suffolk), drops 1.6 with Marist and 1.8 with Suffolk (because Huntsman's support is disproportionately with older voters unlike Paul's whose support is disproportionatel with young and middle age voters.)
There is a another article that also looks at the age distribution issue, claiming it favors Romney. What they don't look at, apparently, is more detailed breakdowns (because although the general claims are true, various candidates have other strengths (for example Ron Paul does well in the 45-54 age group). But the article is from National Journal, so name credibility also helps.
I hope to locate exit poll distributions before the polls close, but competing demands for time (I still need to look at undecideds and others who may switch votes... particularly those who switch to Huntsman, before I get back to exit poll analysis. With a 6 hour time zone lag vs. Eastern Standard Time, I guess I won't be getting much sleep tonight. ;-)
According to many folks, pollsters adjust their raw polling data to reflect expected age, sex and geographic demographics. It is not clear how this is done, as I have yet to find a poll that provided this detail (even with polls providing 300 pages of data). If one assumes this is true, I cannot explain why the % of likely voters vs. age groups changes on a daily basis on the highly regarded Suffolk polk as show below:
I also cannot explain why several other major polls vary between each other. The following data is taken from their most recent poll (or in the case of Suffolk, an average of their 9 daily tracking polls).
Nearly all candidates have a different appeal depending on the age of the voter. For some candidates (e.g. Ron Paul) the sensitivity with regard to the age distribution of is quite high (younger voters overwhelmingly prefer him and retirees have some reluctance to choose him). There is even some indication that middle aged voters (45-54, at least within NH) have a strong preference for Ron Paul. Another example is the strong preference of retirees for Newt Gingrich.
Many people talk about debate performance or new commercials as the reason for daily changes in polls as well as the undefined term "momentum". Sometimes one hears or reads (usually a few words or a second or two) about normal random sampling error (inaccurately described as margin of error). But the affect of other deliberate sampling biases like age or voter registration are rarely mentioned. Perhaps this should change.