Europe tour packages on In some areas, such as aesthetics or morality, value judgments are common, but in hard and social sciences they are frequently considered undesirable. variability n. in statistics and experimental design, the degree to which members of a group or population differ from each other. variable n. a quantity in an experiment or test that varies, that is, takes on different values (such as test scores, ratings assigned by judges, and other personal, social, or physiological indicators) that can be quantified (measured). variable-interval schedule (VI schedule) in free-operant conditioning, a type of interval reinforcement in which the reinforcement or reward is presented for the first response after a variable period has elapsed since the previous reinforcement. Reinforcement does not depend on the number of responses during the intervals. Europe tour packages 2016.