This book is about populations that are hard to survey in different ways. It focuses on populations of people rather than establishments or institutions. In an era of falling response rates for surveys (Brick & Williams, 2013; Curtin, Presser, & Singer, 2005; de Leeuw & de Heer, 2002), it may seem that all household populations are hard to survey, but some populations present special challenges of various sorts that make them harder to survey than the general population. Some of these hard-to-survey populations are rare; others are hidden; some are difficult to find or contact; still others are unlikely to cooperate with survey requests. This chapter tries to distinguish the major challenges that make populations hard to survey and reviews attempts to quantify how hard to survey different populations are.
One way to classify the various sources of difficulty is by what survey operation they affect. In this chapter, we distinguish populations that are hard to sample, those whose members who are hard to identify, those that are hard to find or contact, those whose members are hard to persuade to take part, and those whose members are willing to take part but nonetheless hard to interview. These distinctions reflect the main steps in many surveys. First, a sample is selected. Often, the next operation is identifying members of the target population, for example, through screening interviews. Then, the sample members must be found and contacted. Once contact is made, sample members have to be persuaded to do the survey. And, finally, the willing respondents have to have whatever abilities are needed to provide the requested data or special steps have to be taken to accommodate them. As we shall see, with any given population, problems can arise with each of these operations, making the population hard to survey. And, as will become clear, some hard-to-survey populations present combinations of several kinds of trouble.