Advance Letter

Advance letters (sometimes referred to as “prenotifi-cation” letters) are a means of providing potential respondents with positive and timely notice of an impending survey request. The letters often address issues related to the purpose, topic, and sponsor of the survey and a confidentiality promise. In some surveys, advance letters include a token cash incentive. Letters should be sent by first-class mail and timed to arrive only days to a week ahead of the actual survey contact. They also may be accompanied by other informational materials, such as study-related pamphlets, which are typically designed to address questions about survey participation frequently asked by respondents and, in the case of ongoing or longitudinal surveys, provide highlighted results from previous administrations of the survey.

Long used in survey research efforts, advance letters require only that a mailable address be associated with the sampled unit, regardless of whether that unit is a dwelling, telephone number, or name on a listing. Advance letters are used in conjunction with nearly all survey modes, including face-to-face, telephone, mail, and some Web-based surveys. For example, with random-digit dialed (RDD) telephone surveys, sampled telephone numbers are often cross-referenced with electronic telephone directories and other commercially available databases to identify addresses. In a typical RDD sample, addresses can usually be identified for 50–60% of the eligible telephone numbers. Unfortunately, advance letters cannot be used with survey designs when an identifiable address cannot be determined, such as when respondents in the United States are sampled from a frame of cellular telephone numbers or email addresses. Typically, such frames do not include mailable address information.

In terms of content, most of the research literature and best practice recommendations suggest that an advance letter be brief, straightforward, simple, and honest, providing general information about the survey topic without too much detail, especially if the topic is sensitive. The letter should build anticipation rather than provide details or conditions for participation in the survey. Highlighting government sponsorship (e.g. state), emphasizing confidentiality of the data, expressing advance appreciation, and supplying a toll-free telephone number are typically seen as desirable features. Advance letters can also be used to adjust a variety of other influences known to affect survey participation, including use of official stationery of the sponsoring organization to convey legitimacy; having the letter signed by a person in authority; personalizing the name (when available) and address of the sample household and salutation of the letter to convey the importance of the survey; and providing basic information about the nature of the survey questionnaire to educate the household with regard to the task being requested. Additionally, by alerting a household in advance to an upcoming survey request, the letter can be consistent with the norms of politeness that most unannounced contacts from “salespersons” (or even criminals or scam artists) often violate. Furthermore, advance letters can have a positive effect on the interviewers conducting surveys, enhancing their own confidence in seeking a household's participation in a survey.

Postcards are sometimes used in place of actual letters and are considerably less expensive to produce. They also appear, however, less formal and “official” than a letter might; they are more difficult to personalize; they can include less information about the survey than might be included in a letter; and no incentive can be sent with them (nor should one even be mentioned).

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