One problem with a survey is that it can become a chance to find out "everything we always wanted to know about the welfare population but have not had the chance to ask." Many stakeholders may wish to pursue their own issues through the survey. Once a survey is undertaken, collecting additional information has relatively low cost (up to a point), so the desire to pursue many issues is understandable. For example, most of the interviewer's time in administering a survey is often used in locating the respondent and gaining cooperation, so the cost of adding another 10 minutes to a 30-minute survey may be modest in comparison. Once an interview goes beyond about 45 minutes, however, maintaining respondent cooperation becomes substantially more difficult.
Nonetheless, the more the survey targets key questions of interest, the easier it is to design the survey to get the best results at the lowest cost. For example, if effects of provisions for UP families are of particular interest, it may be useful to oversample these families. If measuring child care costs is a major concern, it may be useful to stratify the sample by the presence of preschool children. If the major goal of the survey is to obtain information on child care and transportation costs, then questions in this area may need to be quite detailed, even if that implies omitting questions on other interesting but less essential topics.