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Biomedical subjects

C S Berkey

Publications and source records attributed to C S Berkey.

63 records · Page 4Linked to original sources
PubMed1982

Bayesian approach for a nonlinear growth model.

Nonlinear least squares methods are currently used for fitting a well-known growth model, namely the Jenss model, to the length measurements of a child followed throughout the first six years of life. An empirical Bayes approach is developed for fitting the model, and the prior distribution of the growth-model parameters is estimated from a large sample of least squares parameters. An expression which is proportional to the posterior distribution is derived so that the posterior mode can be estimated. Given the observations on a child, this posterior mode provides Bayes estimates of the Jenss curve parameters for the child.

Bayes Theorem↗
PubMedDate not supplied

Longitudinal growth standards for preschool children.

The appropriateness of a preschool child's size at a particular age is usually assessed by comparing the child's measurement against growth charts. When the child has measurements at more than one age, the child's percentile status at one age is sometimes compared with the percentile status at a subsequent age, with the purpose of assessing the child's pattern over time or growth rate. This second use of growth charts is not entirely appropriate, for it assumes a high degree of 'tracking' in the population. Healthy children frequently cross percentile lines, the amount of shifting depending upon the age range under consideration, the child's sex, and whether the measurements are length or weight. Thus the correct evaluation of percentile-level changes over time is difficult. We present here conditional standards for length and weight in preschool children, which assess a child's length or weight taking into account previous measurements and/or a current measurement of a second anthropometric variable. The approach can be very flexible as regards ages of measurement, although complete flexibility requires use of a computer. In addition to its clinical application, this approach can be used to predict the future size of a child and may be valuable as an analytic tool in research situations in which control populations are not feasible.

Age Factors↗
PubMedDate not supplied

Longitudinal principal components and non-linear regression models of early childhood growth.

The Jenss curve is a non-linear regression model which describes quite well the longitudinal length or weight measurements of an individual child from three months to six years. It is contrasted with modelling growth by longitudinal principal components analysis, an approach developed by Kent which is not restricted to any particular curve type or age range, and which can be thought of as providing the best fit among linear models having kappa parameters. Thus, in addition to being a model itself, it can be used to evaluate the success of other models. It is shown how this method differs from classical principal components. Data from Longitudinal Studies of Child Health and Development are used to explore these issues.

Child↗
PubMedDate not supplied

Nonlinear growth curve analysis: estimating the population parameters.

A model for analysing longitudinal growth data with covariates is proposed. It assumes that the data for each individual follow a nonlinear growth model, with parameters unique to that individual. The parameters of individuals are assumed to vary in the population, with the population mean of each parameter dependent upon covariates. Several simple, two-stage methods of estimation are described and compared for making inferences about the effects of covariates upon growth. We also present a method of model validation for nonlinear models. These two-stage methods solve the inference problem we encounter when performing multiple cross-sectional analyses of the effects of covariates along the age scale. In addition, these two-stage methods permit us to study the effects of covariates upon growth rate, or other, possibly nonlinear, growth parameters. We find that some methods are better than others at reproducing the covariate effects observed in a series of age-specific analyses of the data.

Age Factors↗
PubMedDate not supplied

Longitudinal analysis of incomplete adolescent data.

An approach is illustrated for the analysis of longitudinal variables collected during adolescence. Since the method requires complete data, three techniques are compared for application when some individuals have missing values. These methods are implemented in a study of systolic blood pressures and dietary fat intakes collected longitudinally in adolescent girls. The value of adolescent systolic and fat variables in predicting systolic pressure in adult women is investigated.

Adolescent↗
PubMedDate not supplied

The distribution of body fat from childhood to adulthood in a longitudinal study population.

Body fat distribution, its continuity from childhood (4-6 years) to 30 years of age, and its link to that of parents is described in a longitudinal study population. A computer-assisted image analysis technique was used to measure body fat distribution (as measured by waist and hip diameters) from somatotype photographs. Pearson correlation coefficients were used to assess the association between the waist/hip diameter ratio (WHDR) and the body mass index (BMI) at all ages and between the WHDR of parents and offspring. Both Pearson correlation coefficients and the Foulkes-Davis tracking index were used to assess tracking of the WHDR from childhood to age 30 years. Stepwise regression analyses were performed to determine the predictability of the WHDR at age 30 years from WHDRs in childhood and adolescence. Among both sexes the WHDR decreased and BMIs increased with age from childhood to 18 years, then both increased from age 18 to 30 years. The correlation between the WHDR and BMI was significant only at 30 years for males (r = 0.37; p < 0.05) and during all stages of adolescence in females (p < 0.05). Age-to-age correlations were high for both sexes (p < 0.0001), and remained significant over a span of up to 25 years. Using the Foulkes-Davis tracking index, tracking from the year of peak height velocity to 30 years (a span of approximately 20 years) was strong for both sexes. Parent and child WHDRs were correlated and differed by sex. Father-son correlations were not significant in childhood, but reached significance in early adolescence (2 years before the year of peak velocity) and remained significant to 30 years (p < 0.05). Mother-daughter correlations were significant at all ages (p < 0.05). The level of the WHDR at the peak of the pubertal growth spurt (year of peak height velocity) predicted up to 58% of the variance in males and 51% of the variance in females of the WHDR at 30 years. We conclude that the adult WHDR (a proxy for the waist/hip ratio) becomes evident by the year of the pubertal growth spurt in height.

Adipose Tissue↗
PubMedDate not supplied

Comparative efficacy of epidural, subarachnoid, and intracerebroventricular opioids in patients with pain due to cancer.

BACKGROUND AND OBJECTIVES: Although rarely used, intracerebroventricular opioid therapy (ICV) is an option for the control of intractable pain due to cancer when systemic treatments have failed. The aim of the present study is to use available data from published trials to compare ICV with the more common epidural (EP) and subarachnoid (SA) opioid treatments in an attempt to establish the utility and safety of ICV. METHODS: Because there are no published controlled trials comparing these routes of administration, the combined data from multiple uncontrolled trials were used, with differences between the treatments analyzed statistically. Trials assessing ICV (13 trials, 268 patients). EPI (29 trials, 909 patients) and SA (21 trials, 410 patients) in cancer patients were identified; data on analgesic efficacy, common pharmacologic side effects, and complications were then extracted and the accumulated incidence data analyzed. RESULTS: The findings (weighted means) indicated ICV to be at least as effective against pain as other neuraxial treatments, with 75% of ICV-treated patients obtaining excellent pain relief as compared with 72% of EPI- and 58% of SA-treated patients (not significant). The failure rate of both spinal treatments tended to be greater than that of ICV and was significantly higher in the case of EPI (P = .045). In general, persistent side effects appeared to be more of a problem with the spinal treatments, while transient symptoms occur more often with ICV. Persistent nausea, urinary retention, and pruritus all were more frequent with the two spinal treatments than with ICV, but transient nausea and respiratory depression occurred more often with ICV. Sedation and confusion appeared to occur more often with ICV than with spinal therapy, while constipation and headache were rarely encountered with ICV. There were no real differences in infectious complication rates among the three treatments (except for a lower rate of infection when an implanted pump was used), but technical problems such as catheter blockage, misplacement, or leakage tended to occur less often with ICV. CONCLUSIONS: Intracerebroventricular therapy appears to be at least as effective against pain as other neuraxial treatments. The ICV technique is the only fixed system that is associated with fewer technical problems than the use of simple percutaneous epidural catheters (difference 9%, standard error of the difference 3.4). The present state of evidence indicates that ICV is a successful treatment for patients with intractable cancer pain and compares well with spinal opioid treatments in terms of efficacy, side effects, and complications.

Analgesia, Epidural↗