Snowball Sampling

Snowball Sampling: Definition

Snowball sampling or chain-referral sampling is defined as a non-probability sampling technique in which the samples have traits that are rare to find. This is a sampling technique, in which existing subjects provide referrals to recruit samples required for a research study.  

For example, if you are studying the level of customer satisfaction among the members of an elite country club, you will find it extremely difficult to collect primary data sources unless a member of the club agrees to have a direct conversation with you and provides the contact details of the other members of the club.

This sampling method involves a primary data source nominating other potential data sources that will be able to participate in the research studies. Snowball sampling method is purely based on referrals and that is how a researcher is able to generate a sample. Therefore this method is also called the chain-referral sampling method.

Snowball sampling is a popular business study method. The snowball sampling method is extensively used where a population is unknown and rare and it is tough to choose subjects to assemble them as samples for research.

This sampling technique can go on and on, just like a snowball increasing in size (in this case the sample size) till the time a researcher has enough data to analyze, to draw conclusive results that can help an organization make informed decisions.

Learn more: Non-Probability Sampling for Social Research

Types of Snowball Sampling

  1. Linear Snowball Sampling: The formation of a sample group starts with one individual subject providing information about just one other subject and then the chain continues with only one referral from one subject. This pattern is continued until enough number of subjects are available for the sample.
  2. Exponential Non-Discriminative Snowball Sampling: In this type, the first subject is recruited and then he/she provides multiple referrals. Each new referral then provides with more data for referral and so on, until there is enough number of subjects for the sample.
  3. Exponential Discriminative Snowball Sampling: In this technique, each subject gives multiple referrals, however, only one subject is recruited from each referral. The choice of a new subject depends on the nature of the research study.

Learn more: How to Determine Sample Size for your Next Survey

Snowball Sampling Method

The nature of snowball sampling is such, that it cannot be considered for a representative sample or in that case for statistical studies. However, this sampling technique can be extensively used for conducting qualitative research, with a population that is hard to locate.  Let us now explore how snowball sampling can be carried out:

Consider hypothetically, you as a researcher are studying the homeless in Texas City. It is obviously difficult to find a list of all the details of the number of homeless there. However, you are able to identify one or two homeless individuals who are willing to participate in your research studies.

Now, these homeless individuals provide you with the details of other homeless individuals they know. The first homeless individual that you found for your research is the primary data. You can collect the information and tabulate data from the primary data source and move on to other individuals who the primary data source has referred to. You as a researcher can continue to tap as many homeless you can find through the reference provided till you know you have collected enough data for your research.

The same strategy can be followed to conduct research or study individuals belonging to certain underground subculture, or individuals who have a hidden identity or are members of a cult etc. who don’t want to be identified easily.  Trust is an important part of any researcher.

Learn more: Secondary Research

An individual, who is ready to share information, needs to know that the information will be used discreetly and this kind of trust is especially important in snowball sampling. For a participant to agree to identify themselves or their group, researchers first need to develop that kind of rapport with the participants. Please know that this sampling technique may consume more time than anticipated because of its nature.  

Snowball sampling analysis is conducted once the respondents submit their feedback and opinions. The data collected can be qualitative or quantitative in nature, and can be represented in graphs and charts on the online survey software dashboard such as the one provided by QuestionPro.

Learn more: Convenience Sampling- Definition, Method, and Examples

Snowball Sampling Applications

Snowball sampling is usually used in cases where there is no precalculated 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).

Thus, this type of sampling is preferred in the following applications:

  • 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.
  • Cases of discord: In case of disputes such as an act of terrorism, violation of civil rights and other similar situations, the individuals involved may oppose giving their statements for evidential purposes. The researchers or management can use snowball sampling, to filter out those people from a population who are most likely to have caused the situation or are witness to the event to gather proof around the event.

Snowball Sampling Examples

For some population, snowball sampling is the only way of collecting data and meaningful information. Following are the instances, where snowball sampling can be used:

  1. No official list of names of the members: This sampling technique can be used for a population, where there is no easily available data like their demographic information. For example, homeless or list of members of an elite club, whose personal details cannot be obtained easily.
  1. Difficulty to locate people: People with rare diseases are quite difficult to locate. However, if a researcher is carrying out a research study similar in nature, finding the primary data source can be a challenge. Once he/she is identified, they usually have information about more such similar individuals.
  1. People who are not willing to be identified: If a researcher is carrying out a study which involves collecting information/data from sex workers or victims of sexual assault or individuals who don’t want to disclose their sexual orientations, these individuals will fall under this category.
  1. Secretiveness about their identity: People who belong to a cult or are religious extremists or hackers usually fall under this category. A researcher will have to use snowball sampling to identify these individuals and extract information from them.

Advantages of Snowball Sampling

  1. 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.
  2. 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.
  3. 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. In snowball sampling, researchers can closely examine and filter members of a population infected by HIV and conduct a research by talking to them, making them understand the objective of research and eventually, analyzing the received feedback.

Disadvantages of Snowball Sampling

  1. 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.
  1. Lack of cooperation: There are fair chances even after referrals, people might not be cooperative and refuse to participate in the research studies.

Learn more about the other Non-Probability Sampling Techniques: