The most important news of the last week was something pollsters tracking the races in Iowa and New Hampshire were probably not so thankful for. New Hampshire Secretary of State Bill Gardner officially confirmed that his state will hold its primary on Tuesday, January 8. The parties in Iowa had already confirmed the Thursday, January 3 as the date for their caucuses. This new calendar, several weeks earlier than in past elections, with fewer days than ever (5) than ever, creates two big challenges for pollsters that give us even more reason to be cautious about the results we will see in the final weeks before the Iowa Caucuses and New Hampshire Primary.
The first issue is that both Christmas and New Year's Day fall in the last two weeks before the Iowa Caucuses. Most pollsters prefer to avoid interviewing in this period because so many Americans are traveling, away from home or otherwise unlikely to participate in a survey. As should be obvious, any random sample will be representative of those who participate. If certain kinds of voters are less likely to be home and reachable during the holiday week, and if those voters have different political preferences than those more likely to be reachable, the results of the survey may be skewed.
Two years ago, I blogged on the topic of December surveys, and reported on a nearly thirty year-old analysis that found much lower response rates in December than other months. However, a more recent study based on the massive data available from government sponsored health surveys (Losch, et. al., Public Opinion Quarterly 66: 594-607) found no difference in contact and cooperation rates in December as compared to other months of the year. However, that study applied only to early December: "All December interviews were completed by the end of the second week of the month" (p. 595).
The Iowa/New Hampshire challenge is made worse by the way the weekends bracket each of these events. Pollsters disagree about whether interviews conducted on weekend evenings (Friday and Saturday nights) introduce similar problems (an issue I discussed in June 2005). Christmas Eve falls on a Monday night, so the last weekday evening before the holidays is Thursday December, December 20. The first weekday evening after New Year's is Wednesday, January 2. So that leaves a two-week window of arguably less than optimal polling conditions right before the Iowa Caucuses.
The next issue, as illustrated best by NBC's First Read, is that the time between Iowa and New Hampshire has been reduced to just five days, including weekend. In the past, polls conducted between Iowa and New Hampshire have tracked big swings over the seven days between the two events, changes that often render the pre-Iowa polls as largely meaningless. In 2004, six different organizations conducted rolling-average nightly tracking that required at least three nights of interviewing to get a clear sense of the changed, post-Iowa landscape. Assuming the same method, those same surveys would not report on pure post-Iowa samplings until Sunday or Monday before the primary, and those results would depend heavily on weekend interviewing.
We will have to wait and see whether pollsters alter their methods and field periods in response to the new calendar. However, the already considerable challenge of sampling likely voters for these two early primaries and measuring their late breaking vote preference will be even tougher in 2008.