Discover what operationalisation means in psychology and how to define variables and hypotheses in measurable terms with clear A-level examples.

Learn what reliability means in psychology, the four main types — test–retest, inter-rater, internal, and external — plus how psychologists test and improve consistent results.

Discover the four main types of validity in psychology — internal, external, construct, and criterion validity — with clear examples and how to improve each for valid research.