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Term Definition

A subset of the population of interest which is selected for inclusion in the research being undertaken.

Sampling bias

A problem with the selection of members of a sample that produces systematic error in the research study. For example, if you wanted to know about what people thought about a service in a particular geographic area one way to select a sample of people in that area would be from the electoral register. However people who have registered to vote are likely to be different from those who have not and therefore, depending on the service, likely to have different views on it. Those views would not be captured due to the way the sample was selected.

Sampling error

The degree of difference between the sample and population from which it was drawn. Only applies to probability sampling.

Sampling frame

A list of all members of the population from which the sample is drawn.

Secondary research

The use of data that were previously gathered for a purpose other than the task in hand. Secondary research can either be qualitative or quantitative. Examples of secondary research would be analysing administrative data (e.g. number of people collecting benefits) to relate it to an issue of interest, or reviewing the existing literature available on a subject.


The respondent fills in answers to a questionnaire without help from an interviewer.

Semi-structured interview

An interview which features closed- and open-ended questions and where the interviewer does not need to keep precisely to a script but can gather more in depth answers based on the research questions and the respondent's answers.

Snowball sample

A non-probability sampling method where the researcher makes contact with one or more potential respondents and asks them for a referral to the next respondent. This method of identifying respondents continues until the required sample size is reached.

Social desirability bias

A distortion of data caused when a respondent provides what they think would be a socially desirable answer rather than their true response.


Statistical Package for the Social Sciences is a software package used for quantitative analysis.

Standard deviation

A measure of dispersion around the mean.

Structured survey

The interviewer reads the questions as structured in the questionnaire and follows the interviewing instructions to this letter. This method ensures that all respondents are treated identically.


A systematic way of collecting data from a number of respondents.

Systematic review

A systematic review is a summary of available research on a given topic that compares studies based on design and methods. It summarizes the findings of each, and points out flaws or potentially confounding variables that may have been overlooked. A critical analysis of each study is done in an effort to rate the value of its stated conclusions. The research findings are then summarized, and a conclusion is provided.