Hockenbury Discovering Psychology 5th txtbk

Measuring Intelligence297The WAIS was revised in 1981, 1997, and most recently, in 2008. The fourthedition of the WAIS is known as WAIS-IV. Since the 1960s, the WAIS has remainedthe most commonly administered intelligence test. Wechsler also developed two testsfor children: the Wechsler Intelligence Scale for Children (WISC) and the WechslerPreschool and Primary Scale of Intelligence (WPPSI).Principles of Test ConstructionWhat Makes a Good Test?Many kinds of psychological tests measure various aspects of intelligence or mentalability. Achievement tests are designed to measure a person’s level of knowledge,skill, or accomplishment in a particular area, such as mathematics or a foreign language.In contrast, aptitude tests are designed to assess a person’s capacity to benefitfrom education or training. The overall goal of an aptitude test is to predict yourability to learn certain types of information or perform certain skills.Any psychological test must fulfill certain requirements to be considered scientificallyacceptable. The three basic requirements of good test design are standardization,reliability, and validity. Let’s briefly look at what each of those requirements entails.StandardizationIf you answer 75 of 100 questions correctly, what does that score mean? Is it high,low, or average? For an individual’s test score to be interpreted, it has to be comparedagainst some sort of standard of performance.Standardization means that the test is given to a large number of subjects whoare representative of the group of people for whom the test is designed. All the subjectstake the same version of the test under uniform conditions. The scores of thisgroup establish the norms, or the standards against which an individual score is comparedand interpreted.For IQ tests, such norms closely follow a pattern of individual differences calledthe normal curve, or normal distribution. In this bell-shaped pattern, most scorescluster around the average score. As scores become more extreme, fewer instances ofthe scores occur. In Figure 7.6, you can see the normal distribution of IQ scores onthe WAIS-III. About 68 percent of subjects taking the WAIS-III will score between85 and 115, the IQ range for “normal” intelligence. Less than one-tenth of1 percent of the population have extreme scores that are above 145 or below 55.achievement testA test designed to measure a person’s levelof knowledge, skill, or accomplishment in aparticular area.aptitude testA test designed to assess a person’s capacityto benefit from education or training.standardizationThe administration of a test to a large, representativesample of people under uniformconditions for the purpose of establishingnorms.normal curve or normal distributionA bell-shaped distribution of individualdifferences in a normal population in whichmost scores cluster around the averagescore.reliabilityThe ability of a test to produce consistentresults when administered on repeatedoccasions under similar conditions.Number of scores2%0.1% 55 7014%68%95%34% 34% 14% 2%“Normal” IQ scores range from85 to 115—the average scoreof 100, plus or minus 15 points.85 100 115 130 145 0.1%Figure 7.6 The Normal Curve of Distri -bution of IQ Scores The distribution of IQscores on the WAIS-III in the general populationtends to follow a bell-shaped normalcurve, with the average score definedas 100. Notice that 68 percent of thescores fall within the “normal” IQ range of85 to 115. Ninety-five percent of the generalpopulation score between 70 and 130,while only one-tenth of 1 percent scorelower than 55 or higher than 145.IQ scoreReliabilityA good test must also have reliability. That is, it must consistently produce similarscores on different occasions. How do psychologists determine whether a psychologicaltest is reliable? One method is to administer two similar, but not identical, versionsof the test at different times. Another procedure is to compare the scores onone half of the test with the scores on the other half of the test. A test is consideredreliable if the test and retest scores are highly similar when such strategies are used.