Samples and Populations

About the lecture

In this lecture, we think about the next step in building an experiment – sampling from a population, focusing in particular on: (i) returning to the example of Bandura, introducing the idea of specific populations for specific studies, noting that a sample doesn’t necessarily always have to cover a breadth of demographics; (ii) the idea of a representative sample, which ensures that the participants used in an experiment are representative of the group(s) you are looking to apply the results of your study to; (iii) sampling methods, covering random and stratified sampling as the ‘gold standard’, with volunteer and opportunity/convenience sampling as lesser (but often more achievable) alternatives; (iv) some of the issues surrounding the volunteer and opportunity sampling methods.

Random Sampling – Random sampling is a process for selecting a sample from a population, such that each individual has the same fixed probability of being included in the sample.

Stratified Sampling – Stratified sampling is a process for selecting a sample from a population comprised of various subgroups (strata), in such a way that all of the subgroups are represented fairly.

Opportunity Sampling – Opportunity sampling is any process for selecting a sample of individuals that is neither random nor systematic, but instead is governed by chance or availability, e.g., interviewing the first 50 people to exit a shop about their experience.

About the lecturer

Dr Eoin O’Sullivan is an associate lecturer in the School of Psychology and Neuroscience at the University of St Andrews. Dr O’Sullivan teaches the first-year undergraduate research methods course and is interested in uncovering novel teaching techniques in the field of research methods and statistics, within psychology. Some of Dr O’Sullivan’s recent publications include ‘Automatic imitation effects are influenced by experience of synchronous action in children’ (2018) and ‘Understanding imitation in Papio papio: the role of experience and the presence of a conspecific demonstrator’ (2022).