Snowball sampling (also known as chain-referral sampling) is a non-probability (non-random) sampling method used when characteristics to be possessed by samples are rare and difficult to find. For example, if you are studying the level of customer satisfaction among elite Nirvana Bali Golf Club in Bali, you will find it increasingly difficult to find primary data sources unless a member is willing to provide you with contacts of other members.
This sampling method involves primary data sources nominating another potential primary data sources to be used in the research. In other words, snowball sampling method is based on referrals from initial subjects to generate additional subjects. Therefore, when applying this sampling method members of the sample group are recruited via chain referral.
Also, snowball sampling is the most popular in business studies focusing on a specific company that involve primary data collection from employees of that company. Once you have contact details of one employee she/he can help you to recruit other employees to the study by providing contact details.
There are following three patterns of snowball sampling:
1. Linear snowball sampling. Formation of a sample group starts with only one subject and the subject provides only one referral. The referral is recruited into the sample group and he/she also provides only one new referral. This pattern is continued until the sample group is fully formed.
2. Exponential non-discriminative snowball sampling. The first subject recruited to the sample group provides multiple referrals. Each new referral is explored until primary data from sufficient amount of samples are collected.
3. Exponential discriminative snowball sampling. Subjects give multiple referrals, however, only one new subject is recruited among them. The choice of a new subject is guided by the aim and objectives of the study.
Application of Snowball Sampling: an Example
Application of snowball sampling involves the following stages:
- Establish a contact with one or two initial cases from the sampling frame. This stage is usually the most difficult one.
- Request the initial cases to identify more cases
- Ask new cases to identify further cases (and so on)
- Stop when:
- a) Your pre-specified sample size has been completed;
- b) There are no further cases left;
- c) Pursuing further cases will make the project unmanageable due to the large size.
If using questionnaire as primary data collection method, you can effectively apply snowball sampling with the use of emails. Specifically, body of the email requesting sample group members to participate in the survey can include a sentence along the following lines:
I would be very grateful if you could provide me with e-mail addresses of other employees in your department/managers who are known to practice democratic leadership style/other people who have bought the same product/etc. who could also participate in this survey.
Advantages of Snowball Sampling
- The ability to recruit hidden populations
- The possibility to collect primary data in a cost-effective manner
- Studies with snowball sampling can be completed in a short duration of time
- A very little planning is required to start primary data collection process
Disadvantages of Snowball Sampling
- Oversampling a particular network of peers can lead to bias
- Respondents may be hesitant to provide names of peers and asking them to do so may raise ethical concerns
- There is no guarantee about the representativeness of samples. It is not possible to determine the actual pattern of distribution of population.
- It is not possible to determine the sampling error and make statistical inferences from the sample to the population due to the absence of random selection of samples
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