Reliability refers to the consistency of research study or measuring test. Reliability can be divided into two categories: internal and external reliability. Internal reliability describes the internal consistency of a measure, such as whether the different questions (known as ‘items’) in a questionnaire are all measuring the same construct. External reliability assesses consistency of a measure from one use to another. For example, if a participant took an IQ test one year, and then took the same test a year later and gained a very similar score, this would show external reliability.