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November 14, 2004

Lessons: Mobile Phones

In today’s Washington Post, Richard Morin provides an important epilogue on the issue of mobile-phone-only voters. As I wrote before the election, some said that polls were missing a hidden Kerry vote among young people who had switched off their home phone service in favor of cell phones. While we had data on the percentage of adults with mobile phones only, we could only guess as to what share they would be of voters and what their preferences would be in the Presidential race. Now, Morin shares some important exit poll data that went unreported on election night:

Buried in the [exit poll] data is the answer to a critical question raised during the campaign about traditional telephone surveys…The exit pollsters cast new light on the issue by asking people leaving the voting booths about their phone service and use.

The good news for pollsters is that only 7 percent of all voters in 2004 were using cell phones as their sole service. The bad news is that this figure swelled to nearly 20 percent among voters between the ages of 18 and 29 years old.

Uh-oh. Not only are there lots of young people without household phone service, but these cell-phone-only voters voted 56 percent to 41 percent for Kerry, meaning missing them in telephone polls could produce polls that underestimated the Kerry vote [emphasis added].

Morin concluded with a point that some may find confusing:

But, happily, one other fact may have saved pollsters, at least during this campaign. Young people with cells were not much more likely to back Kerry than those in homes with traditional phone service only or those who had both cell and traditional service. So missing them wouldn't dramatically skew the results.

Why is that? Most national polls adjust or “weight” their data by age so that the percentage of each age group among all adults on the survey matches what the U.S. Census says it should be nationwide. Surveys will typically under-represent younger people, partly because they are more likely to lack home phone service.  So the weighting procedure essentially replaces one type of 18-to-29 year old (those without home phone service) with another (those who do have home phone service). Morin’s point is that both types of younger voters preferred Kerry by roughly the same margins, so weighting the data by age helped reduce the “skew” in the results.

But not so fast. What about all the other questions on the exit poll? Were cell-phone-only 18-to-29 year olds similar in other respects as well?

More important, what about the cell-phone-only voters over the age of 29? If 20% of 18-to-29 year olds had only cell phones, and 17% of all voters on the exit polls were age 18-to-29, then roughly half of the 7% without cell phones were under 30 (20% * 17% = 3.4%). What about the rest? Were cell-phone-only voters over 30 just like all other voters over 30?

And what happens when the 7% grows to 20%? Morin is right that cell-phone-only voters failed to “dramatically skew” surveys this year but, as I wrote a month ago, “things could be very different next time.”

Related Entries - Mobile phones, Sampling Issues

Posted by Mark Blumenthal on November 14, 2004 at 09:15 AM in Mobile phones, Sampling Issues | Permalink


Mark, do you have a copy of the NEP Exit Poll questionnaire? I note you have the information about the cell phone question. Surely someone has a copy of the document on line somewhere.

Your insight is always appreciated.... esp

Posted by: esp | Nov 14, 2004 3:03:29 PM

RE: Young people and cell phones

More likely, as they age, young people will acquire land lines to go with their cells, as they acquire homes and families. If this is so, things will not change much.

Posted by: Mike | Nov 16, 2004 2:07:09 PM

First, let me that Mr. Blumenthal for his excellent blog. I hope he will keep up the good work. But I must take issue with the two choices he posits as follows:
i) "a slightly higher number of Bush voters than Kerry voters declined to be interviewed;" or
ii) "a massive secret conspiracy somehow shifted roughly 2% of the vote from Kerry to Bush in every battleground state, a conspiracy that fooled everyone but the exit pollsters - and then only for a few hours - after which they deliberately suppressed evidence of the fraud and damaged their own reputations by blaming the discrepancies on weaknesses in their data."

This is a false choice. Correct me if I am wrong, but the exit pollsters never intended their polls be used to detect fraud. It is basic to their method that the vote count is considered right. Therefore, they assume, if the vote count and the exit polls differ, the polls must be adjusted. The fact that this adjustment is done is not a secret and it does not indicate that the pollsters know about fraud and are deliberately choosing to suppers it.

I frankly don't know enough to say whether a massive conspiracy is the only way that the vote count could have been shifted 2% in a number of states. That's what many people like myself would like to get someone to explain.

We wonder this for many reasons. Chief among the reasons is that there is no paper trail. That is not a conspiracy, but it is quite deliberate. Also, perhaps the votes are tabulated on desktop machines that can be remotely accessed, which could lead to more "adjustments." (I don't know this for a fact, but I have heard this.) And we know there are partisan election officials with a troubling track record involved. And now we have this weird exit poll business, including deliberate secrecy on the part of NEP about final results and how the adjusting is done.

I could go on and on, but let me just finish with this one reason people like myself remain curious. Apparently reasonable people cannot ask questions about this issue without being accused of promulgating wild allegations that professional pollsters have "deliberately suppressed evidence of ... fraud" and without the "conspiracy" label being thrown around. That too, makes me wonder what in the world is going on?

Posted by: Anthony England | Nov 17, 2004 11:18:42 PM

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