 Psychology Glossary and definitions. ("V")
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Validity: All tests are designed to measure something; hopefully something specific. If the test does indeed measure what it is intended to measure, then we can say that the test is valid (or has validity). In psychology, tests are usually judged according to their validity and their reliability (if the test produces similar results each time the test is taken). Tests that are valid are also reliable. However a test might be reliable without it being valid. For example, let's say you go to class and your teacher says that he or she has learned that the weight of your head determines the likelihood of you getting cancer. So, each day at the beginning of class the teacher weighs everybody's head on a scale. This continues for one week. Across each day of the week, the weight of your head is going to remain approximately the same; thus we can conclude that the test is reliable. However, is this test valid; does it measure what it is intended to measure (that the weight of your head predicts the likelihood of you getting cancer)? The answer is....NO! So, although the test is reliable, it is not necessarily valid (it does NOT measure what it was designed to measure). Variable: Any characteristic that can assume multiple values or can vary in participants. Variables can include age, gender, body weight, alcohol consumption, attitude and many, many other attributes. Related terms included Independent and Dependent variables. Variable Interval Schedule: If you understand variable ratio schedules, this will be easy. If not, this might be a little confusing at first, but hang on and it will become clear. A variable interval schedule (VI) is a type of operant conditioning reinforcement schedule in which reinforcement is given to a response after specific amount of time has passed (an unpredictable amount of time), but this amount of time is on a changing/variable schedule. This is almost identical to a Fixed-Interval Schedule but the reinforcements are given on a variable or changing schedule. Although the schedule changes, there is a pattern -- the amount of time that must pass changes, but the reinforcement is given after "N"th amount of time passes, where N is the average amount of time that must pass. Let's give an example. You conduct a study in which a rat is put on a VI 10 second schedule (the operant response is pressing a lever). This means that the rat will get reinforced when it waits an average of 10 seconds and then presses the lever. However, because it is an average, the rat may have to wait 30 seconds one trial, then only 2 seconds the next, 30 the next 50 the next, 1 second the next, and so on....just as long as it all averages out to reinforcement being delivered after an average interval of 10 seconds. In addition, sometimes the researcher can make the time interval start all over again if the organism makes an operant response before the proper time has elapsed. So, if the organism makes a response before it is supposed to, the interval starts all over again (if it was supposed to wait 30 seconds on that trial, the 30 seconds starts all over again).
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