An analysis of individual patterns of DQ and IQ curves from 6 months to 17 years

Abstract

The case is made for basing analysis of longitudinal measurement data on each individual's array or curve of scores, and employing methods of analysis which take account of shape of each individual's curve. DQs at 6 months and 18 months, and IQs at 3, 5, 8, 11, 14, and 17 years were available on 84 subjects from 6 months to 17 years, and 109 subjects from 6 months to 14 years, from a London longitudinal project. Scores at each age were converted to SD scores with M = 0, SD = 1. Polynomial equations were fitted to each subject's curve over periods: 6 months − 17 years; 3 years − 17 years; 3 years − 11 years. For whole sample fitted curves yielded highly significant error reduction across all periods, thus rendering untenable doctrine of IQ constancy. Over 6 months to 14 years, 54 per cent of subjects’ curves had a significant fit. Curves differ not only in linear slopes, but in degrees and forms of curvilinearity, particularly over longer periods. A visual method of classification of curves is also presented, which proved effective. Implications of findings are discussed, including that changes in IQ scores cannot be regarded as random variation, but as following systematic trends which differ between subjects; need to regard isolated IQ measures on a subject as derived from a curve of unknown shape and slope; and dangers of treating as equivalent IQs of subjects at different ages. It is concluded that present methods of analysis are applicable to a variety of longitudinal measurement data.

Cognitive status, language attainment, and prereading skills of 6-year-old very preterm children and their peers: the Bavarian Longitudinal Study

“…Fourthly, the assessments of all children were videotaped and subject to constant supervision by one clinical psychologist, and regular feedback seminars were conducted. Finally, the follow-up period extended into the late preschool years, allowing for more certain judgments of long-term problems than assessments in infancy (Hindley and Owen 1979, McCall 1981, Escobar et al 1991, Colombo 1993, McCall and Carriger 1993. The study thus meets and exceeds demands for methodologically sound follow-up studies (Mutch et al 1989, Escobar et al 1991, Ornstein et al 1991, Saigal 1991, Saigal et al 1991, Harrison 1993, Lukeman and Melvin 1993, Siegel 1994, Wolke 1998a).…”

Poor Predictive Validity of the Bayley Scales of Infant Development for Cognitive Function of Extremely Low Birth Weight Children at School Age

“…This poor prediction of cognitive function is considered to be because of difficulties inherent in infant testing, measurement error, change in function of the child, and content of the tests with increasing age, individual and inherited patterns of mental development, and environmental influences that become more evident after 2 years of age. [46][47][48] Aylward 48 noted that 24 months is a critical transition period in cognitive development during which skills in symbolic function, language development, and early concept formation emerge. This finding suggests that the older the child at the time of testing, the predictors of developmental outcomes of ELBW children will be more robust.…”

Cognitive status, language attainment, and prereading skills of 6‐year‐old very preterm children and their peers: the Bavarian Longitudinal Study

“…Fourthly, the assessments of all children were videotaped and subject to constant supervision by one clinical psychologist, and regular feedback seminars were conducted. Finally, the follow-up period extended into the late preschool years, allowing for more certain judgments of long-term problems than assessments in infancy (Hindley and Owen 1979, McCall 1981, Escobar et al 1991, Colombo 1993, McCall and Carriger 1993. The study thus meets and exceeds demands for methodologically sound follow-up studies (Mutch et al 1989, Escobar et al 1991, Ornstein et al 1991, Saigal 1991, Saigal et al 1991, Harrison 1993, Lukeman and Melvin 1993, Siegel 1994, Wolke 1998a.…”