Psychology

Reliability refers to the consistency of a measure. A test is considered reliable if we get the same result when a study is replicated so each time a test is administered to a subject, the results should be the same or similar. Unfortunately, it is impossible to calculate reliability exactly, but it can be estimated in a number of different ways. Including inter-rater reliability, split half reliability and test re-test reliability.

Validity is the extent to which a test measures what it is supposed to measure. It is vital for a test to be valid in order for the results to be accurately applied and interpreted. Validity isn’t determined by a single statistic, but by a body of research that demonstrates the relationship between the test and the behaviour it is intended to measure. There is ecological validity, content validity, concurrent validity and predictive reliability.

Operationalising variables is require in research design, especially in psychology. Operationalization is a process of defining the measurement of a phenomenon that is not directly measurable, though its existence is indicated by other phenomena. It is the process of defining a fuzzy concept so as to make the theoretical concept clearly distinguishable or measurable, and to understand it in terms of empirical observations. In a wider sense, it refers to the process of specifying the extension of a concept—describing what is and is not a part of that concept. For example, in medicine, the phenomenon of health might be operationalized by one or more indicators like body mass index or tobacco smoking. Thus, some phenomena are directly difficult to observe (i.e. they are latent), but their existence can be inferred by means of their observable effects. From about.com and