Home Engineering Behavioral Intervention Research: Designing, Evaluating, and Implementing
The process of selecting a representative sample for a study is called “sampling.” There are two main categories of sampling approaches: probability sampling and nonprobability sampling. Within these categories, there are various methods or procedures that are used to select samples for intervention studies, particularly at the trial phase. These approaches are summarized in Table 9.1. The choice of sampling approach and procedure should be based on the intent of the intervention, specific research goals and questions, the study design, information available about the target population, resources available, and the stage along the pipeline. For example, one typically does not use a probability sampling approach when conducting focus groups early on in the pipeline to gather initial information about perceptions of the need for an intervention. As discussed later in this chapter, this type of approach is more likely to be used when engaged at different stages in the pipeline or in survey research. Before we discuss these strategies, we define the concept of “sampling frame”—a key concept in sampling.
A sampling frame is the “list” or source material that is used to select a sample from a population. For example, if you were conducting a study that was evaluating an intervention to foster safe sex practices among high school students in a particular school region, the sampling frame would be a list of all registered high school students in that region. Examples of sampling frames include an electoral register, telephone directories, employment records, school class lists, patient files in a clinic or hospital, organizational lists, and so on. A sampling frame must be representative of the target population. Oftentimes, a complete sampling frame does not exist. For example, assume that one is relying on use of a telephone directory to conduct a survey about the prevalence of family caregiving within a particular geographic region. This sampling frame would be incomplete, as it would not include people with unlisted numbers or those who have temporary cell phones.
A sampling frame may also be unavailable. A work organization, for example, may not be willing to provide a list of employees; a clinic may not be willing to share the names of patients. In other cases, a sampling frame may not exist because the target population is challenging to identify or reach or may remain hidden—for example, those whose behaviors are illegal (e.g., drug abusers) or individuals who are reluctant to be identified as having a particular characteristic (e.g., persons affected with a specific illness or condition) (Magnani, Sabin, Saidel, & Heckathorn, 2005). As described later, in these cases, other methods such as “snowball sampling techniques” (an initial number of the sample is identified and recruited and helps to identify other individuals to be included in the sample) are used to identify and recruit research samples. In these cases, it is difficult to recruit a representative sample.
TABLE 9.1 Summary of Sampling Methods
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