Testing and Individual Differences for AP Psychology
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Standardization and Norms
Psychometrics is the measurement of mental traits, abilities, and processes. Psychometricians are involved in test development in order to measure some construct or behavior that distinguishes among people. Constructs are ideas that help summarize a group of related phenomena or objects; they are hypothetical abstractions related to behavior and defined by groups of objects or events. For example, we can't measure happiness, honesty, or intelligence in feet or meters. If someone tells the truth in a wide variety of situations, however, we might consider that person honest. Although we cannot observe happiness, honesty, or intelligence directly, they are useful concepts for understanding, describing, and predicting behavior. Psychological tests include tests of abilities, interests, creativity, personality, and intelligence. A good test is standardized, reliable, and valid. After many questions for a test have been written, edited, and pretested, questions are thrown out if nearly everyone answers them correctly or if very few answer them right because these types of questions do not tell us anything about individual differences. Tests that differentiate among test takers and that are composed of questions that fairly test all aspects of the behavior to be assessed are assembled. They are then administered to a sample of hundreds or thousands of people who fairly represent all of the people who are likely to take the test. This sample is used to standardize the test. Standardization is a two-part test development procedure that first establishes test norms from the test results of the large representative sample who initially took the test, then assures that the test is both administered and scored uniformly for all test takers. Norms are scores established from the test results of the representative sample, which are then used as a standard for assessing the performances of subsequent test takers; more simply, norms are standards used to compare scores of test takers. For example, the mean score for the SAT is 500 and the standard deviation is 100, whereas the mean score for the Wechsler Adult Intelligence Scale (IQ test) is 100 and the standard deviation is 15, based on the "standardization" sample. When administering a standardized test, all proctors must give the same directions and time limits and provide the same conditions as all other proctors. All scorers must use the same scoring system, applying the same standards to rate responses as all other scorers. Thus, we should earn the same test score no matter where we take the test or who scores it.
Reliability and Validity
Not only must a good test be standardized, it must also be reliable and valid.
If a test is reliable, we should obtain the same score no matter where, when, or how many times we take it (if other variables remain the same). Several methods are used to determine if a test is reliable. In the test-retest method, the same exam is administered to the same group on two different occasions and the scores compared. The closer the correlation coefficient is to 1.0, the more reliable the test. The problem with this method of determining reliability or consistency is that performance on the second test may be better because test takers are already familiar with the questions. In the split-half method, the score on one half of the test questions is correlated with the score on the other half of the questions to see if they are consistent. One way to do that might be to compare the score of all the odd-numbered questions to the score of all the even-numbered questions. In the alternate form method or equivalent form method, two different versions of a test on the same material are given to the same test takers, and the scores are correlated. The SAT given on Saturday is different from the SAT given on Sunday in October; there are different questions on each form. Although this does not happen, if the same people took both exams and the tests were highly reliable, the scores should be the same on both tests. This would also necessitate high interrater reliability, the extent to which two or more scorers evaluate the responses in the same way.
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