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Cell Phone Only Households by State


There has been a lot of discussion of the Pew Report released earlier this week that shows that including cell-phone only respondents does appear to make a 2-3% difference in the presidential preference polling (see Mark's post). What's most intriguing to me is how this would play out at the state level. Indeed, it seems very unlikely that every state has the same percentage of cell phone only households. Thus, in states with fewer cell-phone only users, the effect of excluding such respondents may have less of an effect on the poll results. On the other hand, states where there are more cell-phone only households may have polling that is further off the mark.

I was hoping to be able to easily find some survey data with enough respondents to get a sense of the prevalence of cell-phone only households in each state. Unfortunately, the 2007 CDC data that is often cited provides more than enough national interviews to accomplish this task, but the dataset hides the state of the respondent, only allowing users to place respondents in a particular Census Region. Nevertheless, we can learn a little about geographical variance from this data. Specifically, families in the South and Midwest are more likely to have cell phones only compared to states in the West and Northeast. Based on this data, we should expect polling from southern and midwestern states to be more prone to error from the cell-phone only problem than polling in other regions.

cell_region.PNG

Another source of data that may be of some use in answering this question is the 2006 Cooperative Congressional Election Study. (In the interests of disclosure, I should say that I am involved in the 2008 version of this study, though I had no role in the 2006 version.) This was a large (approximately 30,000 respondents) internet survey conducted by YouGov/Polimetrix using a matched random sample design. Because this is an internet survey, it probably isn't as ideal for addressing this question as the CDC survey would be. However, the sample was stratified to assure that there would be a large enough sample from each state and since the state of the respondent is available for this data (and isn't for the CDC data), it is the one decent way I've found of breaking out cell-phone only figures by state.

In this survey, 10.6% of respondents indicated that they only had a cell-phone (this is smaller than the percentage cited in the CDC survey, though the CDC survey was conducted a year later). Most interesting is the variation across states. The map below shows this variance.

cellonly_states.PNG

Some of the swing states that stand out as having higher than average cell-phone only users are Montana (21%), Oregon (17%), Virginia (15.7%), Wisconsin (15.3%) and Minnesota (15.1%). (Keep in mind that these figures are from two years ago). If this survey is providing reasonably accurate figures on cell-phone only users, then it may be the case that polling of these states would be particularly prone to under-stating support for Obama. It may also explain why the polling in some of these states (for example, Virginia) has been so erratic.

Of course, these data may be problematic and should be taken with some caution. If anyone has ideas about other sources that could be used to compile state-by-state measures of cell-phone only households, please let me know. If excluding cell-phone only respondents does matter, then it would be nice to have a strong sense of where it will matter most.

 

Comments
s.b.:

If your hypothesis is correct with regards to swing state polls you could easily see if pollsters who survey cell phones are reporting the higher numbers for Obama, as the assumption is that it increases his support. I do not necessarily share this conclusion, but you seem to. It would be relatively easy for you to compile the data on these polls. Supporting your hypothesis would get a lot more respect from me than just making assumptions.

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Clint Cooper:

This is very good stuff. Thank you for posting it. I will be interested to see if MS, MT, and ND turn out a little different than expected for Obama on election day. Or even Virginia, for that matter.

WI, OR, MS, VA, and MT were all states where Obama greatly outperformed his pre-election poll numbers during the primary, and they are all states with a high percentage of cell-phone-only users.

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Mark:

Recall that Obama outperformed his average primary polling margin by 7.2 in the South, 3.1 in the Midwest, 1.1 in the West and -1.8 in the Northeast. This ordering is exactly mirrored by the ordering of incidence of cell phone only users by region. Could there be a correlation here?

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judas_priest:

sb:

That compasrison has already been done. Nate Silver at fivethirtyeight.com compared pollster that were land-line only to those who include cell phones. On average the land-line only firms showed Obama 2.3% lower than those pollsters whose sampled included cell-phones.

Because we cannot be sure that there are not other differences between the two groups of pollsters we cannot be sure that entire gap is due to the cell-phone issue, but it is suggestive. The difference wss statistically significant at the 95% confidence level.

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zelduh:

Query:

What about people (like me) who use Skype (or Vonage or T-Mobile VOIP)? Are we counted in the LANDLINE or Cell phone category?

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independent voter:

I would say that the cell phone polling problems are overrated as both cell and landlines are polled. Ther are also many people that use internet phone-what classification do they fall under? In my opinion, the online politcal blogs are also skewed in favor of younger voters as the are the most frequent users. Does this mean they are also not a fair opinion of the population in general?

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W David:

Internet phones are classified as land-line phones. Cellphones are unlisted numbers, so many of the pollsters and campaigns don't have access to their numbers. That is one of the reasons why the Obama campaign cleverly asked people to sign up for a text message of the announcement of his VP choice. That gave the campaign access to the hundreds of thousands of cellphone users. Also, a disproportionate amount of African Americans don't have landlines at all (as well as cellphones). Though we know that Obama will probably get over 90 percent of the African American vote, it's harder to figure out the level of voter turn-out if you can't get an accurate measure of African American registered voters and likely voters.

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tanygeo:

i like this particular article. it gives me an additional input on the information around the world thanks a lot and keep going with posting such information.
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mobile phone

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