Table 13: Non-probability sampling strategies
Sampling strategy Summary
Availability or convenience sampling Availability sampling refers to the technique in which the selection of sample is due to researcher accessibility. The limitation of this strategy is selection bias. An example of this strategy is sample from facility or institution where the researcher is employed.
Successive sampling Successive sampling is when individuals are selected successively, for example, an exit interview with patients after an encounter with the health provider. All patients who just met with the doctor are offered the opportunity to participate in the study. If the study involves multiple sites, a combination with stratified sampling can be used. However, the patients are selected successively in each stratum.
Purposive sampling Purposive sampling is used when the elements are selected based on the researcher’s judgment regarding the desired information being collected. Participants are being selected on their knowledge of the topic being studied. The example of purposive sampling is a survey using a panel of experts.
Snowball sampling or respondent driven sampling This type of sampling strategy is suitable to recruit participants who are members of a hidden population (e.g. victims of domestic violence, drug users). Snowball sampling is started when a researcher can identify the first participant that met selection criteria. The researcher then asks these participants to identify people with similar experiences or characteristics. To increase the variability of characteristics of the study participants, the researchers can ask the subsequent participants to find the next participants with the same experience but with different socio- demographic characteristics, for example with different gender, age group, socio-economic