Public Opinion Quarterly Advance Access originally published online on July 13, 2009
Public Opinion Quarterly 2009 73(3):484-496; doi:10.1093/poq/nfp035
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Unintended Consequences
The Cost of Purging Business Numbers in RDD Surveys
Address correspondence to Daniel M. Merkle; e-mail: daniel.m.merkle{at}abc.com.
Survey researchers commonly use RDD (random digit dialing) samples that are purged of listed business telephone numbers to increase interviewer productivity by removing numbers that are assumed to be ineligible for household surveys. This study investigates this practice and finds an unintended consequence: an increase in household noncoverage. The data come from national RDD surveys using samples that were not purged of listed business numbers. Phone numbers were flagged as listed businesses or not and respondents were asked about how their phone lines are used. Five percent of respondents were interviewed on lines classified as business numbers that normally would have been purged from the sample. But were these valid household interviews or should they have been excluded? The data show that these are, in fact, primarily households. Ninety-four percent of these numbers rang at residences. Moreover, these phone numbers are used as household rather than business-only lines. Ninety-three percent said any adult in the household can answer the phone line in question. A more important finding is that business-line purging increases noncoverage. Sixty-five percent of those contacted on numbers that normally would have been purged from the sample said they had no other phone lines in the household—a noncoverage rate of 3.6 percentage points had these numbers been excluded from the sample. The study concludes with an examination of the characteristics of those interviewed on presumed business numbers, and considers the cost/benefit implications of including these numbers in the sample.
DANIEL M. MERKLE is with ABC News, 147 Columbus Ave., 4th Floor, New York, NY 10023, USA. GARY LANGER is with ABC News, 7 W. 66th St., New York, NY 10023, USA. JON COHEN is with The Washington Post, 1150 15th St. NW, Washington, DC 20071, USA. LINDA B. PIEKARSKI is with Survey Sampling International, LLC, 6 Research Drive, Shelton, CT 06484, USA. ROBERT BENFORD is with GfK Custom Research North America, 1060 State Road, Princeton, NJ 08540, USA. DAVID LAMBERT is with TNS, 410 Horsham Rd., Horsham, PA 19044, USA. This is a revised version of a paper presented at the annual conference of the American Association for Public Opinion Research, Montreal, Canada, May 18–21, 2006.
Editors' Note: This article was accepted for publication before Daniel Merkle joined the editorial team as an associate editor. It is the policy of POQ not to allow editors or associate editors to publish in the journal.