Experimental Designs

About the lecture

In this lecture, we introduce experiments, focusing in particular on: (i) recognising experiments as the ‘gold standard’ in research design, due to their ability to establish the presence of causal relationships between variables; (ii) two key terms in experimental design – independent and dependent variables, talking through what each refers to; (iii) outlining how to identify an experiment as a method of study; (iv) the different types of experiments; (v) the benefits and drawbacks of laboratory, field, and natural experiments in the context of differing types of validity and unwanted effects on the results; (vi) within and between subjects designs, including matched design as a sub-type of between-subjects design.

Laboratory Experiment – Scientific study conducted in a laboratory or other such workplace, where the investigator has some degree of control over the environment and can manipulate the independent variable(s).

Field Experiment – A study conducted outside of the lab in a 'real-world' setting.

Naturalistic Experiment – Data collection in a field setting, without laboratory controls or manipulation of variables. These procedures are usually carried out by a trained observer, who watches and records the behaviour of participants in their natural setting.

Within-Subjects Design – Also known as a repeated measures design, within which the effects of treatments are seen through the comparison of scores from the same participant observed under all of the experimental conditions.

Between-Subjects Design – Also known as an independent groups design, within which participants are assigned to only one of the experimental conditions and each person provides only one score for data analysis.

Matched-Pairs Design – A derivative of the between- subjects design involving two participant groups in which each member of one group is paired with a similar participant from the other group(s). Participants may be 'similar' if they share one or more characteristics that are not the main focus of the study but could still influence the outcome.

Order Effects – In a within-subjects design, order effects are the influence of the order in which treatments are administered or tasks are completed. This can result in performance differences between participants which are not due to variables of interest to the study. This can be combatted through counterbalancing.

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).