Cell-Phone-Only Voters in the 2008 Exit Poll

Michael Mokrzycki, Associated PressScott Keeter, Pew Research Center

Courtney Kennedy, University of Michigan and The Everett Group

American Association for Public Opinion ResearchHollywood, Florida

May 2009

Research questions

• Cell-phone-only incidence & rate of growth

• How do CPO voters differ from landline-reachable?– Demographics and political attitudes– Comparison to 2004 exit poll

• Bias implications for future surveys that don’t attempt to cover the wireless-only population

Historical context

• We’re now a quarter-century into the cell phone age– Motorola DynaTAC (1983)

• 1990s: heyday of list-assisted RDD

Historical context

• This decade– Wireless substitution becoming widespread– RDD HH coverage back to early 1960s levels

Do cells harm surveys?

• Until recently, CPO were small fraction of US population/households

• Differences were small or non-existent between subgroups most likely to be cell-only and their LL-reachable demographic cohorts

• Typically, post-stratification weighting cured what minor ills existed

Recent caution flags

• Cell-only population keeps growing

– By second half of 2008, 20% of US households were cell-only, outnumbering landline-only (Blumberg and Luke 2009)

• Emerging evidence: small but persistent Dem bias

– Three Pew surveys in summer 2008 consistently found 2- to 3-point shift toward Obama when including cell interviews

2008 NEP national exit poll

• In-person survey: Opportunity to reach cell-only voters

2008 NEP national exit poll

• In-person survey: Opportunity to reach cell-only voters

CAVEATS:

Subject population: Voters who cast ballots on Election Day

Excludes 33% of 2008 electorate who voted early/absentee

(NEP did cover early voters in 18 states and nationally with landline RDD but no cell sample)

NEP national exit poll methodology

• Stratified probability sample of 300 precincts nationwide

• Random selection of voters within each precinct (interval – every nth voter)

• Self-administered PAPI

NEP national exit poll methodology

• Four versions of questionnaire; phone-status question on two of them

• Same question asked in 2004 national exit poll

Methodology – sample sizes

• 2004 N = 5,619– Including 385 cell-phone only

• 2008 N = 7,341 – Including 1,496 cell-phone-only

Good news: Bigger N in 2008

to study the cell-only population!

Household telephone statusin Election Day exit polls

Presidential vote by HH phone statusin Election Day exit polls

CPO status by agein Election Day exit polls

Growing – and aging – CPO populationin Election Day exit polls

• Growing majority of cell-only voters are age 30+– 2004: 52%– 2008: 57%

• CPO growth rate higher among older age groups than among younger (albeit on smaller 2004 bases)

• Increasing adoption of cell-only status by older people

• Younger voters aging + maintaining phone habits

CPO: select demographicsin 2008 Election Day exit polls

• TOTAL cell-phone-only: 20%

• Did not complete HS: 27% (post-grad 14%)• Income: < $15k: 37%; $15-50k: 26%• Hispanic/Latino: 28% (white 19%, black 22%)• Party ID: D 21%, R 17%, I 20%• Ideology: Lib 24%, Mod 21%, Cons 16%

Pres. vote by age and phone statusin 2008 Election Day exit polls

47%

55%

63%

65%

69%

47%

47%

51%

63%

61%

0% 10% 20% 30% 40% 50% 60% 70% 80%

50+

40-49

30-39

25-29

18-24

Percent Voting for Obama

Ag

e

Has landline

Cell-only

**

Difference significant at ***p<.001 **p<.01 *p<.05

Pres. vote by age and phone statusin 2008 Election Day exit polls

• From 2004 to 2008, bigger differences between LL-reachable and CPO among both < 30 and 30+

• But the differences increased at a faster rate among older voters

Pres. vote by age and phone statusin 2008 Election Day exit polls

LL 18-29 CPO 18-29 LL 30+ CPO 30+

2004

Kerry56% 58% 46% 49%

2008

Obama62% 67% 48% 56%

Other variables by phone statusin 2008 Election Day exit polls

• Some variables produced no sig. diff. between CPO and LL-reachable.

• One curious result:

– No difference on worry about direction of nation’s economy in next year

– But CPOs were a little more likely than LL-reachable to call the current condition of the nation’s economy “poor”

Other variables by phone statusin 2008 Election Day exit polls

• Some variables did show sig. differences. Often related to partisanship/ideology:

– CPOs a bit more “excited” than LL-reachable about an Obama presidency (by 6 points)

– CPOs 10 points more likely to strongly disapprove of Bush job performance, and to say McCain would continue Bush’s policies

Voter mobilization by phone statusin 2008 Election Day exit polls

• Cell-only voters were far more likely (22%) than those with landlines (10%) to have voted for first time in 2008

– Naturally this correlates strongly with age: youngest voters most likely to be cell-only and also most likely to be new voters

GOTV by phone statusin 2008 Election Day exit polls

• Cell-only Election Day voters were far less likely to have been contacted by either campaign. – 74% of CPO said not contacted by either campaign, vs 56% of

LL-reachable

• Even Obama's campaign – renowned for its technological innovation – was more likely to contact LL-reachable than CPO-voters– 34% of LL-reachable reported contact from Obama campaign,

vs 23% of CPO

GOTV by phone statusin 2008 Election Day exit polls

• So it’s not only pollsters who have trouble reaching those who are wireless-only.

Possible reasons for political differences between CPO and LL

• Likely stem from socio-economic differences – CPO less affluent and, among older voters, less educated.

– Income differences large and consistent: more cell-only voters have incomes below $50,000 in all age groups. In particular:

• 30-39: 47% of CPO < $50k vs 28% of LL-reachable• 40-49: 50% of CPO < $50k vs 25% of LL-reachable

– Income and education were strong predictors of presidential voting in 2008, and may explain at least part of the differences in presidential preference by telephone status.

But a “phone effect” remains

• Multivariate regression analysis: – differences in presidential preference persist even when

controlling for all available demographic variables

• Some CPO characteristics distinguish them politically from other voters but weren’t in the NEP exit poll– marriage, children in the home, homeownership, and religiosity

and church attendance

Meta-analysis of pre-election polls

• No compelling evidence that sample design affected accuracy of the difference between the candidates

• But there is evidence that the point estimates for each candidate were systematically affected, a little– Polls that excluded wireless were most likely to underestimate

Obama vote (generally by 2-3 points)– Consistent with previous studies– In 2008, post-survey weighting still sufficient cured these “ills”

Conclusions

• No sign cell-only growth is slowing

• Small but consistent bias in ‘08 pre-election polls w/o CPOs

• Clear difference in presidential vote in exit polls by phone status

• CPO incidence growing at faster rate among 30+ than younger voters – and older CPO voting more Dem in 2008 than 2004

Conclusions

• No evidence that non-coverage bias from excluding CPOs might diminish rather than grow in coming years

• Many national pre-election pollsters concluded in 2008 that they needed to include cell samples. Still true.

• Also true for the early voting component of the “exit polls” – need cell coverage in the phone polls NEP conducts the week before the election to capture “advance” voters

Thank you!

• mike@mikemokr.com• skeeter@pewresearch.org• ckkenned@umich.edu