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 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.
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.
Types 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.
1. 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.
2. 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.
3.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.
Examples of snowball sampling
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.
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.
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.
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
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
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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