Vitamins and intelligence tests.
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The minimum standard deviations achievable for concurrent estimates of thresholds and psychometric function slopes as well as the optimal target values for adaptive procedures are calculated as functions of stimulus level and track length on the basis of the binomial theory. The optimum pair of targets for a concurrent estimate is found at the correct response probabilities p1 = 0.19 and p2 = 0.81 for the logistic psychometric function. An adaptive procedure that converges at these optimal targets is introduced and tested with Monte Carlo simulations. The efficiency increases rapidly when each subject's response consists of more than one statistically independent Bernoulli trial. Sentence intelligibility tests provide more than one Bernoulli trial per sentence when each word is scored separately. The number of within-sentence trials can be quantified by the j factor [Boothroyd and Nittrouer, J. Acoust. Soc. Am. 84, 101-114 (1988)]. The adaptive procedure was evaluated with 10 normal-hearing and 11 hearing-impaired listeners using two German sentence tests that differ in j factors. The expected advantage of the sentence test with the higher j factor was not observed, possibly due to training effects. Hence, the number of sentences required for a reliable speech reception threshold (approximately 1 dB standard deviation) concurrently with a slope estimate (approximately 20%-30% relative standard deviation) is at least N = 30 if word scoring for short, meaningful sentences (j approximately 2) is performed.
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Scores on the K-SNAP, a new brief cognitive measure designed to assess neuropsychological functioning in adolescents and adults, were correlated with KAIT IQs, a comprehensive test that measures fluid and crystallized intelligence. The sample included 33 adolescent and adult patients hospitalized for depression. The K-SNAP correlated significantly higher with fluid than crystallized intelligence.
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The stability of IQ from childhood to adulthood in low-birthweight subjects was measured in two independent samples with follow-up intervals of approximately 14 and 9.5 years. In both samples, intelligence was assessed with the WISC at a mean age of 9.5. Twenty-six subjects were retested with the WAIS at a mean age of 23.5, and 78 subjects with the BPP (the Danish Military Draft Board Intelligence Test) at the age of 19.1. Both samples obtained childhood and adult test scores below the expected means. For the Wechsler Verbal, Performance and Full-Scale IQs, the stability quotients were 0.86, 0.86, and 0.89 in the WAIS sample, and the retest correlations for the three IQs with the BPP score were 0.66, 0.65, and 0.74. Thus, the majority of children showed stable patterns of intellectual development from middle childhood to young adulthood.
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There is no doubt about the reality of the secular increase in cognitive test scores. However, there is disagreement about a key issue: does the observed increase reflect a genuine upward trend in intelligence? Evidence from the Raven test is clear, although there are some doubts about its adequacy as a fine-grained measure of fluid intelligence. Evidence from the so-called 'method of correlated vectors' is much less clear. When a crystallized battery is considered, the results leave little doubt: the increase does not reflect gains in general intelligence. However, when a fluid battery is analysed, the increase does reflect gains in general intelligence. The present study uses one of the best available measures of fluid intelligence (the Culture-Fair intelligence test) to provide new evidence for the secular increase in fluid intelligence, beyond the findings from the Raven test and the method of correlated vectors. A total of 4498 Spanish high school students and high school graduates were tested within a time interval of 20 and 23 years, respectively. The results show that there is a clear upward trend in intelligence. Moreover, students show an average increase equivalent to 6 IQ points, while graduates show an average increase of 4 IQ points. Therefore, more selected people (graduates) show a smaller increase than less selected people (students). Some implications are discussed.
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When using tests of infant development and intelligence in children born prematurely, the subject's age is commonly corrected for the degree of prematurity. However, there is disagreement: first, on whether this correction should ever be applied, and second, at what age to discontinue the adjustment. In a theoretical model, the difference between corrected and uncorrected scores in early infancy was massive and the difference remained clinically important until the age of 8.5 years in children who were born extremely prematurely. The clinical implications of using corrected or uncorrected scores were then evaluated in 174 very low birthweight children without severe sensorineural disabilities and with paired Bayley Mental Development Index (MDI) and Wechsler Preschool and Primary Scales of Intelligence (WPPSI) full scale scores. Failure to correct for prematurity reduced the mean MDI by 12.1 points but reduced the mean WPPSI by only 4.1 points. The disparity between individual MDI and WPPSI scores increased significantly with decreasing gestational age if uncorrected scores were used (P = 0.015) but not if scores were corrected. Using corrected scores, the MDI correctly predicted the WPPSI category in 86.1% of children (P less than 0.001) but in only 54.6% using uncorrected scores (the difference was not significant). It is suggested that a practical solution to the dilemma is to correct test scores for prematurity in the age range 2-8.5 years recognizing that only in extremely immature infants will uncorrected scores be substantially lower than corrected ones at a later age.