Advance Letters as a Means of Improving Respondent Cooperation in Random Digit Dial Studies: A Multistate Experiment

Advance letters can potentially reduce the degree of nonresponsein random digit dial (RDD) surveys; however, they can also havea heterogeneous impact on subgroups, disproportionately raisingparticipation rates among certain segments of the populationand thereby having a detrimental effect on nonresponse bias.This is, in part, because advance letters can only be used inRDD surveys with the subset of respondents for whom an addresscan be identified. It may also be related to who in a householdsees the letter. We assess whether the use of advance letterscan improve the level of participation in the Behavioral RiskFactor Surveillance System (BRFSS) without introducing otherpotential data biases. The data reported here corroborate previousfindings, in terms of the positive impact that advance letterscan have on overall response rates (approximately a 6-percentage-pointgain). Moreover, the advance letters were cost-efficient inthat the cost of obtaining a fixed number of completed surveysusing advance letters was lower than the cost without letters.However, the positive impact of the advance letter on reducingnonresponse may have been offset to some extent in that theadvance letter may have biased the sample of those who completedthe interview toward older, white respondents and those of highersocioeconomic status, and away from younger, nonwhite individualsand persons with lower education and income levels. This lattergroup was underrepresented in the final sample and also lesslike to remember having received a letter.