Survey researchers are usually concerned with choosing respondents within households after households are selected randomly. Within-unit coverage and non-response are key issues, so researchers want to select the correct respondent and gain his or her cooperation. Each of these goals has costs. One popular quasi-random compromise is the last-birthday (LB) method of selecting respondents from within a sampled household in random-digit dialing surveys. It circumvents the pitfalls of pure or nearly pure random methods by being relatively quick, easy, and likely to secure cooperation. Probability methods can involve a potentially lengthy and intrusive process of querying the informant (person who answers the phone) about all household members eligible to be interviewed before selecting the correct respondent from the resulting list.
An example of LB question wording ...
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