Cell Phones for Data Collection: Costs and Challenges Michael Link 1, Michael Battaglia 2, Martin Frankel 3, Larry Osborn 4, and Ali Mokdad 5 1 Nielsen Media Research 2 Abt Associates Inc. 3 Baruch College, City University of New York 4 Knowledge Networks 5 Centers for Disease Control and Prevention

The Plague of Cell Phones!!!

Cell phones and telephone surveys Reliance on cell phones increasing (July- December NHIS): 57.1% of households have a working cell phone 11.6% of households (11.8% of adults) are cell phone only 25.4% for age 18-24, 29.1% for age 25-29, 54.0% of unrelated adult households w/o children, 26.4% for renters Result: increased potential for noncoverage bias Cell Phone Summit 2005, TSM II 2006, AAPOR 2007 – special issue of POQ

Cell phones and telephone surveys Conducting surveys via cell phones can be operationally challenging Cell phone frame may not be that efficient Geographic specificity is a problem Cannot use autodialers/predictive dialers Charges for incoming calls/minutes used Safety concerns Potential mode effects / measurement errors Level of cognitive engagement

Behavioral Risk Factor Surveillance System (BRFSS) Monthly state-based landline RDD survey of health issues and related risk factors 50 states, District of Columbia, Puerto Rico, Guam, and Virgin Islands 350,000+ adult interviews conducted in 2006 Significant declines in participation overall, particularly among younger adults and males

2007 BRFSS cell phone pilot Conducted in Georgia, New Mexico, & Pennsylvania Target: 200 cell & landline / 200 cell-only adults (per state) 1,200 total interviews Abbreviated BRFSS core interview: 66 questions minutes (on average) Incentives: $10 post-paid incentive for completing the detailed interview $1 for completing the screener

Sample design Marketing Systems Group (MSG): All designated cellular 1,000 banks Implicit stratification by area code and exchange Equal probability sample of telephone numbers Survey Sampling Inc. (SSI): All 100 series banks designated as cellular Mixed use (landline / cell phone) banks containing zero residential directory-listed numbers Implicit stratification by FIPS, carrier, & 100-block Systematic random sample of 100 blocks Randomly generate last 2 digits of number

Screening questions Introduction Confirmed telephone number Is this a cellular telephone? Are you 18 years of age or older? Are you a resident of (state)? Do you also have a landline telephone that is used to make and receive calls? Yes – took subsample of respondents No – took all respondents

Survey Participation Rates

Calculation of rates Used detailed disposition codes modeled after Callegaro et al (2007) with some modifications/additions Included ring, no answer and voice mail as working residential numbers Only cases confirmed by company message as being not in service were excluded Used AAPOR response rate guidelines Calculated separate rates for: Screening for eligible respondent Completion of interview

Participation rates GANMPA Starting sample size:9,0004,4009,997 Completed interviews: % Working cell numbers: Screener rate: Interview rate: Response rate:

Interview rate by landline access

Percent working cell number by sample vendor

Comparison of respondent demographics

Landline and Cell phone populations and frames CELL PHONELANDLINE ABC

Landline surveyCell phone survey Percent male State equalized design weight applied

Landline surveyCell phone survey Percent years State equalized design weight applied

Landline surveyCell phone survey Percent Hispanic State equalized design weight applied

Landline surveyCell phone survey Percent black State equalized design weight applied

Landline surveyCell phone survey Percent high school or less education State equalized design weight applied

Landline surveyCell phone survey Percent married State equalized design weight applied

Summary of significant differences across demographic subgroups Cell only v.s. cell & landline adults (from cell phone survey): Significant differences for 12 of 24 subgroups examined Particularly age, employment status & marital status Cell & landline adults (cell phone survey v.s. landline survey): Significant differences for 11 of 24 subgroups examined Particularly sex, race, marital status, and children in household

Comparison of key survey estimates

Landline surveyCell phone survey Percent any kind of health care coverage State equalized design weight applied

Landline surveyCell phone survey Percent not received care due to cost barrier State equalized design weight applied

Landline surveyCell phone survey Percent currently smoke cigarettes State equalized design weight applied

Landline surveyCell phone survey Percent ever tested for HIV State equalized design weight applied

Landline surveyCell phone survey Percent binge drink past 30 days State equalized design weight applied

Comparison of Survey Costs

Cost per Interview Data collection costs only Level of effort: RDD = 7.4 calls/case Cell = 3.2 calls / case Response rate: RDD = 38% Cell = 26% Interview length: RDD = 25 minutes Cell = 12 minutes $60 $74 $196

What have we learned? Group with both landline & cell phone differ across landline and cell phone surveys Mode effect? Response/nonresponse effect? Frame effect? This is an important issue when we try to combine landline & cell phone surveys Cell phone only group differs significantly from landline group on some health variables, but not others Risk behaviors seem most problematic

What have we learned? Cell phone & landline usage varies significantly across states Makes use of national estimates from the NHIS for post survey adjustment problematic Compared to landline surveys, cell phone surveys: Have lower rates of response at the screener stage But similar rates at the interview stage Working residential rates lower, but not as bad as expected Are considerably more expensive, especially if we decide to screen for cell-only adults

Future directions Problem is not going away, but will continue to worsen Focus on combining estimates from cell and landline frames (Frankel and Battaglia are working on this for the BRFSS) Cell only households not the only problem Need more focus on primary cell users Best to reach by landline or cell frame? Mode effects – what measurement issues are raised by interviewing via cell phones?