Here, we will discuss five types of non-probability sampling, which are;
- Convenience Sampling
- Quota Sampling
- Purposive Sampling
- Consecutive Sampling
- Snowball Sampling
1. Convenience (or accidental) Sampling
As the name suggests, convenience sampling involves the collection of data where it is most readily available to the researcher. Convenience sampling is also known as accidental sampling because respondents are chosen whenever and wherever they are met. Convenience sampling is used in cases where certain target populations aren’t easily accessible or when researchers have a limited time frame.
For example, if a study about the consumption patterns of coffee is conducted, a researcher may choose to visit different coffee shops in order to collect information from customers at these shops.
While employing the method of convenience sampling, it is important that the researcher avoids turning his sample group into a biased one, as this will lead to inaccurate findings in the study.
2. Quota Sampling
Quota sampling is used in cases where the study aims to represent variables such as age, gender, income, occupation, or any other certain group. As this method of sampling involves the grouping of people with certain similar characteristics, it can be considered a form or proportionate stratified sampling (a component of probability sampling). However, in this case, the predetermined proportion of people will be sampled from different groups based on convenience.
For example, if you want to conduct a study with 55% male participants, you may choose to include male participants readily available to you until you have reached the required number/size of your quota.
3. Purposive (or judgemental) Sampling
As mentioned earlier, most researchers are interested in particular target populations. Purposive sampling, also known as judgemental sampling, is a method in which researchers choose respondents based on who is in the best position to provide the required information.
For example, if you were to conduct a study on the spending habits of millionaires, you would only be able to acquire first-hand information from those who have built their net worth into the millions, and therefore, those people must be chosen as respondents.
4. Snowball Sampling
Snowball sampling is a method of non-probability sampling that is used when the target population of the study is inaccessible or hard to find. In this case, the researcher contacts someone who meets the criteria to be included in their sample group and then asks them to recommend other potential respondents who they may know who meet the criteria.
For example, if I’m doing a study on Native Americans, an ethnic group that is only 1.6% of the American population, it may be advantageous for me to use the snowball sampling method. After finding one or a few Native Americans, they may be able to give me a list of contacts of more Native Americans that they may know (relatives or friends, for instance).
5. Consecutive Sampling
Consecutive sampling, also known as total enumerative sampling, is a method of sampling where a researcher works with a sample group over a period of time, then picks a new sample group to work with again, and so on until they’ve acquired the amount of data they require. This is similar to convenience sampling, with the difference that there are multiple sample groups over the course of the study.