Glossary

A sample is a subset of a population.

The process of selecting and examining a portion (a sample) of a larger group of potential participants (a population) in order to produce inferences that apply to the broader group of participants.

Source: Encyclopaedia of Quality of Life and Well-Being Research.

A sampling frame is a comprehensive list of all the members of the population from which a probability sample will be selected.

Source: SAGE Research Methods.

SPSS is a commercial statistics package. Visit the website for more information.

Standard error measures the uncertainty or variability associated with a sample estimate when compared to the true population parameter. The standard error of a statistic (like a mean or percentage) indicates how much that statistic is expected to vary from the true population value.

The standard error is also inversely proportional to the sample size; the larger the sample size, the smaller the standard error.

Source: Stat Trek Statistics Dictionary.

A statistical model is a theoretical construction of the relationship of explanatory variables to variables of interest created to better understand these relationships.

They typically consist of a collection of probability distributions and are used to describe patterns of variability that data may display.

The statistical model is expressed as a function. For example, a researcher may model a linear relationship using the regression function below:

y = b₀ + b₁x₁ + b₂x₂ … + b_ix_i

In this model, y represents an outcome variable and x_i represents its corresponding predictor variables. The term b₀ is an intercept for the model. The term b_i is a regression coefficient and represents the numerical relationship between the predictor variables and the outcome for the ith term.

Statistical modelling is a major topic. Readers who want to know more will find extensive accounts of statistical models including linear regression and logistic regression in statistical texts and online.

Sources: Science Direct; Magoosh Statistics Blog.

Stratified random sampling refers to a sampling method in which the total population is divided into non-overlapping subgroups. Each of the subgroups is called a stratum, and two or more subgroups are called strata.

Sources: An Introduction to Statistical Methods and Data Analysis; Stat Trek Statistics Dictionary.

A structured interview follows a strict protocol using a set of defined questions administered in the same order to all interviewees. It allows for a quick collection of focused data, however there are limited opportunities for probing and further exploration of topics. The interviews are usually conducted face to face or over the phone.

Survey design involves a series of methodological steps to create an effective survey, such as defining an objective, determining a target population, designing the questionnaire etc.

Survey design can also refer to the structure or format of the survey, such as a cross-sectional survey, longitudinal survey etc.

Survey nonresponse can occur at both an item and unit level.

Item nonresponse occurs when a sample member responds to the survey but fails to provide a valid response to a particular item (e.g. a question they refuse to answer).

Unit nonresponse occurs when eligible sample members either cannot be contacted, refuse to participate in the survey or do not provide sufficient information for their responses to be valid. Unit nonresponse can be a source of bias in survey estimates and reducing unit nonresponse is an important objective of good survey practice.

Source: SAGE Research Methods.