Snowball sampling is an important non-probability sampling where a chain referrel exist. A researcher first select a respondent to collect data then this respondent refers one or more respondent and in this chain everyone refer one or more respondent until the requirements of the researcher fulfilled.
Snowball sampling is a chain referral sampling. It’s a non-probability sampling where existing study subjects recruit future subjects from among their acquaintances. Thus the sample group is said to grow like a rolling snowball. This sampling technique is often used in hidden populations, such as drug users or sex workers, which are difficult for researchers to access.
Example of snowball sampling
Steps in Snowball Sampling
- Identify the population to study
- Choose some samples to get the snowball rolling
- Ask the initial subjects to nominate others who they know fit the description of potential subjects
- Repeat the above process until you have sufficient data
Types of Snowball Sampling
- Linear Snowball Sampling: Subject refers only one other subject
- Exponential Non-Discriminative Snowball Sampling: Subject gives multiple referrals and each referral gives some more until required sample size is reached.
- Exponential discriminative Snowball Sampling: Subject refers multiple people but only one is chosen as sample
Snowball sampling is usually used in cases where there is no pre-calculated list of target population details (homeless people), there is immense pain involved in contacting members of the target population (victims of rare diseases) , members of the target population are not inclined towards contributing due to a social stigma attached to them (hate-crime, rape or sexual abuse victims, sexuality, etc.) or the confidentiality of the organization respondents work for (CIA, FBI or terrorist organization).
- Medical Practices: There are many less-researched diseases. There may be a restricted number of individuals suffering from diseases such as progeria, porphyria, Alice in Wonderland syndrome etc. Using snowball sampling, researchers can get in touch with these hard to contact sufferers and convince them to participate in the survey research
- Social research: Social research is a field which requires as many participants as possible as it is a process where scientists learn about their target sample. When social research is to be conducted in domains where participants might not necessarily willing to contribute such as homeless or the less-fortunate people.
- It’s quicker to find samples: Referrals make it easy and quick to find subjects as they come from reliable sources. An additional task is saved for a researcher, this time can be used in conducting the study.
- Cost effective: This method is cost effective as the referrals are obtained from a primary data source. It’s is convenient and not so expensive as compared to other methods.
- Sample hesitant subjects: Some people do not want to come forward and participate in research studies, because they don’t want their identity to be exposed. Snowball sampling helps for this situation as they ask for a reference from people known to each other. There are some sections of the target population which are hard to contact. For example, if a researcher intends to understand the difficulties faced by HIV patients, other sampling methods will not be able to provide these sensitive samples.
Disadvantages/ Downsides of snowball sampling
- Sampling bias and margin of error: Since people refer those whom they know and have similar traits this sampling method can have a potential sampling bias and margin of error. This means a researcher might only be able to reach out to a small group of people and may not be able to complete the study with conclusive results.
- Lack of cooperation: There are fair chances even after referrals, people might not be cooperative and refuse to participate in the research studies.