2. Stabiliry. There are a variety of ways of examining the reproduceability of a measure administered on different occasions. For example, one might ask about the degree of agreement between different observers (inter-observer reliabiliny); the agreement between observations made by the same rater on two different occasions (infra-observer reliability); observations on the patient on two occasions separated by some interval of time (rest-retest reliability), and so forth. As a minimum, any decision regarding the value of a measure should be based on some information regarding stability of the instrument. Internal consistency, in its many guises, is not a sufficient basis upon which to make a reasoned judgement.