Self-selection sampling is a type of non-probability sampling technique. Non-probability sampling focuses on sampling techniques that are based on the judgement of the researcher [see our article Non-probability sampling to learn more about non-probability sampling]. This article explains (a) what self-selection sampling is, (b) how to create a self-selection sample, and (c) the advantages and disadvantages of self-section sampling.
Self-selection sampling is useful when we want to allow units, whether individuals or organisations, for example, to choose to take part in research on their own accord. When we talk about people or organisations that could make up part of our sample, we refer to these as a unit or a case [see our article, Sampling: The basics, if you are unsure about the terms unit, case, sample and population].
As a sampling strategy, self-section sampling can be used with a wide range of research designs and research methods. For example, survey researchers may put a questionnaire online and subsequently invite anyone within a particular organisation to take part. Scientists that conduct experiments using human subjects may advertise the need for volunteers to take part in drug trials or research on physical activity. The key component is that research subjects (or organisations) volunteer to take part in the research on their own accord. They are not approached by the researcher directly.
There may be a wide range of reasons why people (and organisations) volunteer for such studies, including having particularly strong feelings or opinions about the research, a specific interest in the study or its findings, or simply wanting to help out a researcher(s).
The self-selection sample involves two simple steps: (a) publicising your need for units (or cases); and (b) checking the relevance of units (or cases) and either inviting or rejecting them.
You need to let potential applicants or organisations know about your study. This will involve some kind of advertising or promotion, whether print media, the radio, an online notice board, or some other medium. The invitation will need to follow certain ethical guidelines, making it clear what the study involves, but also more practical information, such as the types of applicant that are required (e.g., age, gender, or some other more subject-specific criteria).
Imagine that a researcher wants to understand more about the career goals of students at a particular university. Let?s say that the university has roughly 10,000 students. These 10,000 students are our population (N). Each of the 10,000 students is known as a unit. In order to select a sample (n) of students from this population of 10,000 students, we could choose to use self-selection sampling. Let's imagine that because we have a small budget and limited time, we choose a sample size of 100 students. However, it is important to the sampling strategy that each of the students is in their final year of university. Therefore, you would need to ensure that only final year students took part in the research. To publicise this, the study could run an advertisement on student radio, the student newspaper, or on physical and online notice boards accessed by students at the university.
Not all applicants will be relevant to your study. They may have not all read or understood what the study is about. Furthermore, they may not be the type of applicants you are looking for. For example, students that are not in their final year at the university may still choose to apply to take part in the study. You will need to check this before any particular unit or case, whether an individual or organisation, is invited to become part of your sample.
Since the potential research subjects (or organisations) contact you:
This can reduce the amount of time necessary to search for appropriate units (or cases); that is, those individuals or organisations that meet the selection criteria needed for your sample.
The potential units or cases (individuals or organisations) are likely to be committed to take part in the study, which can help in improving attendance (where necessary), and greater willingness to provide more insight into the phenomenon being studied (e.g., a respondent many be more willing to spend the time filling in qualitative, open-ended questions in an online survey, where others may leave them blank).
Since the potential research subjects (or organisations) volunteer to take part in the survey:
There is likely to be a degree of self-selection bias. For example, the decision to participate in the study may reflect some inherent bias in the characteristics/traits of the participants (e.g., an employee with a 'chip of his shoulder' wanting to give an opinion).
This can either lead to the sample not being representative of the population being studied, or exaggerating some particular finding from the study.
Despite the potential disadvantages of self-selection sampling, it is a popular sampling technique in many areas of science that require human subjects, as well as human trials within the pharmaceutical industry. As such, whilst self-selection sampling does not benefit from the random choice of subject selection as probability sampling does, or the theoretical drivers of purposive sampling, it is an effective sampling strategy in experimental research settings.