Reliability of Random Digit Dialing Calls to Enumerate an Adult Female Population

Challenges to random digit dialing have been documented, but the reliability of random digit dialing outcomes from telephone number calling, household identification, and enumeration has never been addressed, despite its potential to bias population representativeness by affecting completeness of coverage. The authors explored interobserver reliability of calls to numbers generated by random digit dialing for a 1990–1996 population-based case-control study in San Francisco, California, area women, using data from a quality control effort in which 122 of 4,890 random digit dialing numbers were assigned to a second interviewer for recontacting within 4 months. The 34 numbers discrepant between the first and second calls did not differ from the 88 unchanged outcomes, and reliability was good (kappa = 0.65, 95% confidence interval: 0.55, 0.75). Eligibility (an adult woman in the household) was confirmed for nine of 11 eligible households. However, six of 29 households originally ineligible because of gender were eligible on recontact, and eligible residences rose from 24% to 39% between the two calls, although the two groups of eligible women did not differ in age or race. This underenumeration of women by random digit dialing confirms prior observations, although interviewer differences or changes in respondents or household composition between the first and second calls may have contributed. Recontact of gender-ineligible households may improve completeness of random digit dialing coverage for female populations.