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Anna Nagy

Chapter 5: Measurement Concepts Reliability of Measures Reliability refers to the consistency or stability of a measure of behavior. A reliable measure of a psychological variable such as intelligence will yield the same result each time you administer the intelligence test to the same person. The test would be unreliable if it measured the same person as average one week, low the next and bright the next. Put simply, a reliable measure does not fluctuate from one reading to the next. A more formal way of understanding reliability is to use the concepts of true score and measurement error. Any measure that you make can be thought of as compromising two components: 1) a true score, which is the real score on the variable and 2) measurement error . An unreliable measure of intelligence contains considerable measurement error and so does not provide an accurate indication of an individuals true intelligence. In contrast, a reliable measure of intelligence one that contains little measurement error will yield an identical (or nearly identical) intelligence score each time the same individual is measured. To illustrate the concept of reliability further, imagine that you know someone whose true intelligence score is 100. Now suppose that you administer an unreliable intelligence test to this person each week for a year. Now suppose that you test another friend who also has a true intelligence score of 100; however, this time you administer a highly reliable test. What might your data look like? In each case, the average score is 100. However scores on the unreliable test range from 85 to 115, whereas scores on the reliable test range from 97 to 103. The measurement error in the unreliable test is revealed in the greater variability shown by the person who took the unreliable test. Researchers cannot use unreliable measures to systematically study variables or the relationships among variables. Trying to study behavior using unreliable measures is a waste of time because the results will be unstable and unable to be replicated. Reliability is most likely to be achieved when researchers use careful measurement procedures. It might mean paying close attention to the way questions are phrased or the way recording electrodes are placed on the body to measure physiological reactions.
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