Multiple prepubertal growth spurts in children of the Fels Longitudinal Study: comparison with results from the Edinburgh Growth Study.

BACKGROUND: Contrary to the common assumption of a single midspurt, the heights of children measured at 6-monthly intervals in the Edinburgh Growth Study appear to show multiple prepubertal growth spurts of 2-3 years duration. The Edinburgh study relied on inspection of empirical accelerations to identify the spurts. AIM: The work aimed to study this phenomenon with velocity maxima and minima of kernel-smoothed heights in the more extensive 6-monthly data from the Fels Longitudinal Growth Study. Velocity maxima and minima for two sets of triplets in the Fels data were also examined for concordance of prepubertal growth patterns in the identical and fraternal members. SUBJECTS: Subjects were 167 boys and 152 girls with complete or nearly complete 6-monthly height measurements from 2 to 18 years of age. METHODS: Because the number of spurts detected by kernel smoothing was found to be sensitive to the bandwidth of the smooth, a preliminary study to determine the best choice of bandwidth was carried out. With the chosen width, 2.0 years, the number and locations of up to five maxima and preceding minima of growth velocity were determined for each case. Statistics for the distribution of age of occurrence, height, and velocity at each turning point were computed for cases having no or one to four prepubertal growth spurts. RESULTS: Good agreement with the Edinburgh results was found. Numbers of prepubertal spurts varied from zero to four in both boys and girls. Later maturing children tended to have more spurts. Among the Fels triplets, the patterns of prepubertal growth of the identical members of each set did not appear more concordant with each other than with the fraternal member. CONCLUSIONS: The finding of similar appearing prepubertal multiple growth spurts over 2-3-year intervals by different analytical methods in two widely separated populations strongly supports the generality of this phenomenon. The timing and duration of the spurts do not suggest, however, a systematic origin. Rather, they appear to be episodes of random change in rate of growth prior to the onset of adolescence, under the constraint of the genetically determined growth potential.

Interpretation of a full-information item-level factor analysis of the MMPI-2: normative sampling and nonpathognomonic descriptors.

An exploratory item-level full-information factor analysis was performed on the normative sample for the MMPI-2 (Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989). This method of factor analysis, developed by Schilling and Bock (Bock & Schilling, 1997) and based on item response theory, works directly with the response patterns and avoids the artifacts associated with phi coefficients and tetrachoric coefficients. Promax rotation of the factor solution organizes the clinical scale items into 10 factors that we labeled Distrust, Self-Doubt, Fitness, Serenity, Rebelliousness, Instrumentality, Irritability, Artistry, Sociability, and Self-Reliance. A comparison was made to the results of Johnson, Butcher, Null, and Johnson (1984), who performed a principal-component analysis on an item set of 550 items from the previous version of the MMPI (Hathaway & McKinley, 1943). Along with version changes and sampling differences, the essential differences between Johnson et al.'s results and ours may be attributed to differences between the Schilling and Bock method, which uses all information in the item responses, and the principal-component analysis, which uses the partial information contained in pairwise correlation coefficients. This study included 518 of the complete 567 items of the MMPI-2, versus Johnson et al.'s retention of 309 of the initially included 550 items of the previous MMPI. The full-information analysis retained all 518 initially included items and more evenly distributed the items over the 10 resulting factors, all sharply defined by their highest loading items and easy to interpret. Sampling effects and factor label considerations are discussed, along with recommendations for research that would validate the clinical utility of the implied scales for describing normal personality profiles. The full-information procedure provides for Bayes estimation of scores on these scales.

High-dimensional multivariate probit analysis.

A computationally practical form of probit analysis for multiple response variables based on an assumed common factor model for the latent tolerances is proposed. Numerical integration over the factor space provides maximum likelihood estimation of the probit regression parameters and of the probabilities of response combinations under the model. The procedure is applied to five variables from the Pneumoconiosis Field Trial, two variables of which were previously analyzed by Ashford and Sowden (1970, Biometrics 26, 535-546).

Comparison of height acceleration curves in the Fels, Zurich, and Berkeley growth data.

A new type of smoothing spline designed for nonparametric estimation of growth acceleration curves was applied to longitudinal measures of height from the Fels, Zurich, and Berkeley growth studies. Landmark features of the individual acceleration curves were located and examined for site effects and site by sex interaction. The curves in each group were structurally averaged by transforming the age scale of each child to align the landmarks with overall means. The modal shapes of the structural average curves were found to be highly similar in the three studies, although the relative number of children who conformed to the modal pattern differed among the studies. Significant site by sex interactions were found in the timing of the landmarks associated with the pubertal growth spurt and with the prepubertal 'midspurt'.

Age changes in adult stature: trend estimation from mixed longitudinal data.

Although it is widely accepted that persons become shorter as they grow older, most estimates of the rate of decline are based largely on cross-sectional studies and are confounded by secular changes and individual variation. The present study uses a mixed series of longitudinal physical measurements, obtained by the Busselton Population Studies Group, for nearly the entire adult population of Busselton, Western Australia. All persons in the sample who had a minimum of three measures at 3-year intervals are included in our analysis, regardless of health. Random regressions analysis of the individual height and age data is used to estimate the expected rate of decline of stature with age. A significant sex difference was found, with females declining at a greater rate than males, particularly after the age of 40.

Tonic, phasic and cortical arousal in Gilles de la Tourette's syndrome.

This study explored the hypothesis that Gilles de la Tourette's syndrome involves a disturbance in arousal modulation. The experimental group consisted of 20 unmedicated subjects with the Gilles de la Tourette's syndrome, and the control group of 20 subjects with chronic medical illnesses (haemophilia, von Willebrandt's disease and diabetes). There were differences between groups in the manner in which log conductance level changed over time during sound and light habituation experiments involving mild levels of stimulation with the Gilles de la Tourette group showing less change in arousal level over trials than the control group. No group differences were found in measures of phasic arousal, rate of spontaneous fluctuations and performance on two tasks that have been related to cortical arousal. It is suggested that the slower change in log conductance level in the Gilles de la Tourette group during the sound and light habituation experiments indicates that reticular activity is more persistent in these patients.

A lod score method for detecting linkage on the X chromosone between a marker locus and a major gene locus for a quantitative.

A sequential lod-score method is proposed for detecting linkage on the X chromosome between a marker locus and the locus of a major gene influencing a quantitative trait, The method uses information from sons of doubly heterozygous mothers. The average number of families required to detect linkage is substantially less than that of the fixed sample-size method proposed by Hill.