Frequent Pollster.com readers will know that the Cell Phone Only (CPO) population is a subject I blogged on frequently during the campaign. One of the reasons for this interest is because there is still a lot we don't know about CPOs at this point (I like a good mystery). In this post, I want to present a little analysis that demonstrates just how much we still have to learn about CPOs.
CPOs wouldn't be nearly as fascinating if their distinctiveness could be easily explained by their age or other basic demographic or political factors. One view is that CPOs are just younger, more urban, and more mobile and that once you account for these factors, CPOs behave pretty much just like their landline counterparts. Last year, however, a Pew report suggested that the differences might not be that simple when they discovered that weighting alone might not be enough to account for CPOs.
To explain why this is the case, I used some of the data Pew relied on to publish that report (in this case, Pew's June 2008 Voter Attitudes Survey). In this survey, Pew interviewed respondents both on landline phones and on cell phones (see more on the methodology here). What I wanted to know was whether CPOs are really that different from landline users once you account for demographic and political factors?
To answer this question, I estimated a multivariate statistical model that would allow me to take into account any demographic or political information that the Pew survey collected that I could imagine would explain the difference between CPOs and the rest of the public. I controlled for age, gender, education, ethnicity, race, income, home ownership, marital status, and whether the respondent lived in an urban area. In addition to these demographic factors, I also accounted for the partisan affiliation of the respondent. If these factors explained the difference between CPOs and landline respondents, then we wouldn't expect to find any measurable difference between these groups once we've controlled for them.If you enjoy reading output from statistical models, you can get that information . However, the key information is presented in the chart below. The chart shows the probability of a landline or CPO respondent registering a vote preference for Obama, McCain, or neither candidate after controlling for the demographic and political factors.
This chart indicates that even after controlling for all of the demographic and political factors listed above, CPOs still had distinctive vote preferences relative to those with landlines in their homes. While landline respondents were 49% likely to prefer Obama in June, CPOs were 65% likely to do so. These differences can't be explained as a result of CPOs being younger, or because they were single, or because they lived in urban areas, or even because they were more likely to be Democrats. Essentially, if you had two people who were the same on all of the factors mentioned above, the one without a landline would still be more likely to support Obama than the one with a landline.
If it isn't age, income, education, or even mobility, then what makes CPOs distinctive from those with landlines? Is it something more inherent about embracing a CPO lifestyle? Perhaps it is an outlook on life that makes CPOs more willing to cast off traditions and venture into something new? Perhaps a higher tolerance for taking risks and embracing change? Or something else entirely? We still don't have a good handle on what makes CPOs so distinctive, which is why this makes for such a great mystery.
(Note: I'm using this Pew data to examine another reason why CPOs may cause pollsters so much trouble--because it may be more difficult to pin down whether they are actually going to vote. I'll present some analysis on that topic in my next post.)