Researchers use this sampling method if the sample for the study is very rare or is limited to a very small subgroup of the population. This type of sampling technique works like chain referral. After observing the initial subject, the researcher asks for assistance from the subject to help identify people with a similar trait of interest.
The process of snowball sampling is much like asking your subjects to nominate another person with the same trait as your next subject. The researcher then observes the nominated subjects and continues in the same way until the obtaining sufficient number of subjects.
For example, if obtaining subjects for a study that wants to observe a rare disease, the researcher may opt to use snowball sampling since it will be difficult to obtain subjects. It is also possible that the patients with the same disease have a support group; being able to observe one of the members as your initial subject will then lead you to more subjects for the study.
Types of Snowball Sampling
Linear Snowball Sampling
Exponential Non-Discriminative Snowball Sampling
Exponential Discriminative Snowball Sampling
Advantages of Snowball Sampling
The chain referral process allows the researcher to reach populations that are difficult to sample when using other sampling methods.
The process is cheap, simple and cost-efficient.
This sampling technique needs little planning and fewer workforce compared to other sampling techniques.
Disadvantages of Snowball Sampling
The researcher has little control over the sampling method. The subjects that the researcher can obtain rely mainly on the previous subjects that were observed.
Representativeness of the sample is not guaranteed. The researcher has no idea of the true distribution of the population and of the sample.
Sampling bias is also a fear of researchers when using this sampling technique. Initial subjects tend to nominate people that they know well. Because of this, it is highly possible that the subjects share the same traits and characteristics, thus, it is possible that the sample that the researcher will obtain is only a small subgroup of the entire population.