David C. Hamilton

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• PhD
• Professor Emeritus at Dalhousie University

Background While there is increasing interest in identifying pregnancies at risk for adverse outcome, existing prediction models have not adequately assessed population-based risks, and have been based on conventional regression methods. The objective of the current study was to identify predictors of fetal growth abnormalities using logistic regre...

Background: The objective of this study to develop percentile curves for cardiometabolic disease markers in a population-based sample of Canadian children and youth. Methods: The analysis used data from 6116 children and adolescents between 6 and 19 years of age who participated in the Canadian Health Measures Survey cycles 1 (2007/2009), 2 (200...

Background: Linkage disequilibrium (LD) is the non-random association between alleles at different loci and remains important for disease mapping studies in humans. A common measure of LD is the sample correlation between indicator variables for alleles at the 2 loci. Knowledge of LD estimate precision may help inform biomedical decisions based on...

In Halifax, Nova Scotia, 149 victims of the 1912 sinking of the Titanic lie beneath petrologically identical “black granite” headstones. These headstones, supplied by the White Star Line, arrived in Halifax in late 1912, but no known historical document reveals their source. They consist of medium- to coarse-grained olivine-bearing gabbro, with cum...

In Halifax, Nova Scotia, 149 victims of the 1912 sinking of the Titanic lie beneath petrologically identical "black granite" headstones. Those headstones, supplied by the White Star Line, arrived in Halifax in late 1912, but no known historical document reveals their source. They consist of medium- to coarse-grained olivine-bearing gabbro, with cum...

Background. Skinfold thickness (SFT) measurements are a reliable and feasible method for assessing body fat in children but their use and interpretation is hindered by the scarcity of reference values in representative populations of children. The objective of the present study was to develop age- and sex-specific percentile curves for five SFT mea...

Background: Skinfold thickness (SFT) measurements are a reliable and feasible method for assessing body fat in children but their use and interpretation is hindered by the scarcity of reference values in representative populations of children. The objectives of the present study were to develop age- and sex-specific percentile curves for five SFT m...

Background: Skinfold thickness (SFT) measurements are a reliable and feasible method for assessing body fat in children but their use and interpretation is hindered by the scarcity of reference values in representative populations of children. The objectives of the present study were to develop age- and sex-specific percentile curves for five SFT m...

The Marshall–Olkin extended two-parameter bathtub distribution is introduced and its structural properties are investigated, including the compounding representation of the distribution, the shapes of the density and the hazard rate function, the moments and quantiles. Estimation of the model parameters by maximum likelihood is discussed. Applicati...

Body mass index (BMI) is commonly used to assess a child's weight status but it does not provide information about the distribution of body fat. Since the disease risks associated with obesity are related to the amount and distribution of body fat, measures that assess visceral or subcutaneous fat, such as waist circumference (WC), waist-to-height...

This paper deals with the estimation of reliability R = P[Y < X] when X and Y are two independent random variables with atwo-parameter bathtub shaped failure rate distribution with the samesecond shape parameter. Likelihood and Bayesian methods are proposedto make inferences about R. We obtain the likelihood interval andasymptotic confidence interv...

In the face of increasing extinction rates, it is vital to have estimates of relative and absolute species abundance and their relationship to important factors. For species that live in the oceans or large lakes, this can be a difficult task. Here, we present a method for estimating absolute abundance from a single binary acoustic time series. The...

IntroductionSpinal muscular atrophy (SMA) is a severe autosomal recessive genetic disease that occurs in about one in every 10 000 births. Prenatal carrier testing is available for SMA and the utility of universal screening is actively debated.Objective To perform a systematic review and meta-analysis of SMA genotype frequency, carrier frequency an...

New one-parameter and two-parameter distributions are introduced in this paper. The failure rate of the one-parameter distribution is unimodal (upside-down bathtub), while the failure rate of the two-parameter distribution can be decreasing, increasing, unimodal, increasing-decreasing-increasing, or decreasing-increasing-decreasing, depending on th...

In eutherian mammals, one X-chromosome in every XX somatic cell is transcriptionally silenced through the process of X-chromosome inactivation (XCI). Females are thus functional mosaics, where some cells express genes from the paternal X, and the others from the maternal X. The relative abundance of the two cell populations (X-inactivation pattern,...

Genotypic counts of paired relatives discordant for a complex late-onset disease are often used to test for genetic association. The power of the various statistical test options, when data on covariates are unavailable, has been the focus of recent research. Comparison of the Cochran-Armitage, Bhapkar, and McNemar tests indicates that none is supe...

A two-parameter distribution was revisited by Chen (2000) [7]. This distribution can have a bathtub-shaped or increasing failure rate function which enables it to fit real lifetime data sets. Maximum likelihood and Bayes estimates of the two unknown parameters are discussed in this paper. It is assumed in the Bayes case that the unknown parameters...

Short daily periods of binocular exposure (BE) can offset longer single daily episodes of monocular exposure (ME) to prevent the development of deprivation amblyopia. To determine whether the outcome depended upon an absolute daily amount of BE or its proportion of the daily visual exposure, daily mixed visual input of 3 different durations (3.5, 7...

The trans effect (TE) in the present context refers to the electronic compensation which in collinear homoligand L—Z—L* trans bond pairs lengthens the Z—L* bond when the Z—L bond is shortened. The existence of a functional relation d* = f(d) between the conjugated bond lengths d(Z—L) and d*(Z—L*) (d and d* not equivalent by symmetry; population A)...

The two-parameter linear failure rate distribution has been used quite successfully to analyze lifetime data. Recently, a new three-parameter distribution, known as the generalized linear failure rate distribution, has been introduced by exponentiating the linear failure rate distribution. The generalized linear failure rate distribution is a very...

We propose an approximate maximum likelihood method for estimating animal density and abundance from binary passive acoustic transects, when both the probability of detection and the range of detection are unknown. The transect survey is purposely designed so that successive data points are dependent, and this dependence is exploited to simultaneou...

Statistical inference for the parameters in three competing risks models is considered in this paper. It is assumed that there are more than two causes of failure. The maximum likelihood procedure is used to derive point and asymptotic confidence interval estimates of the unknown parameters. The risks due to each cause of failure are investigated....

The relationships between the structural complexity of coniferous forests and the epiphytic lichen com- munities that inhabit them were examined in 51 conifer-dominated stands in southwestern Nova Scotia. One hundred and fifteen lichen species were studied in stands in the age range of 50–300 years. Envi- ronmental variables shaping the structural c...

Loci exhibiting Hardy-Weinberg disequilibrium (HWD) are often excluded from association studies, because HWD may indicate genotyping error, population stratification or selection bias. For case-control studies, HWD can result from a genetic effect at the locus. We extend the modelling to accommodate both stratification and genetic effects. Theoreti...

Key aspects of the expression of long-term potentiation (LTP) and long-term depression (LTD) remain unresolved despite decades of investigation. Alterations in postsynaptic glutamate receptors are believed to contribute to the expression of various forms of LTP and LTD, but the relative importance of presynaptic mechanisms is controversial. In addi...

Renal stone formation due to hypercalciuria is a relatively common disorder with clear evidence for genetic predisposition, but cryptic phenotypic heterogeneity has hampered identification of candidate genes. The R990G single-nucleotide polymorphism (SNP) of the calcium sensing receptor (CASR) gene has been associated with hypercalciuria in stone f...

Exact confidence regions for all the parameters in nonlinear regression models can be obtained by comparing the lengths of projections of the error vector into orthogonal subspaces of the sample space. In certain partially nonlinear models an alternative exact region is obtained by replacing the linear parameters by their conditional estimates in t...

Methods of estimation and inference are presented for the situation where two non-linear regression models with unequal error variances contain some parameters in common. Such a situation arises in structural chemistry, when bond lengths are available for three nearly collinear atoms in crystals and a model is required to quantify the extent and fo...

The construction of approximate joint and marginal confidence regions for parameters in the first-order autoregressive time series model is discussed. These regions are based on the large sample distributions of the likelihood ratio (and approximations to it), of the maximum likelihood estimates and of the score statistics. All these approaches are...

We described the approximate variance for a composite measure of linkage disequilibrium (LD), which depends only on genotype frequencies and allows for departure from Hardy-Weinberg disequilibrium (Hamilton et al. 2006). Here we extend this work to allow for inferences about differences in composite LD coefficients, as we illustrate with two exampl...

The approximate variance for the standardized measure of gametic linkage disequilibrium has been described. However, this approach assumes knowledge of the phase of double heterozygotes or Hardy-Weinberg equilibrium. Here we give the approximate variance for a composite measure of linkage disequilibrium which depends only on genotype frequencies. W...

To estimate cystic fibrosis (CF) birth rates in Canada from 1971 to 2000 and to assess the population impact of genetic testing in families with a history of CF, after identification of the CF transmembrane conductance regulator gene in 1989. Age-at-diagnosis data were obtained from the Canadian Cystic Fibrosis Foundation Patient Data Registry and...

The maximum and minimum are obtained for a composite measure of linkage disequilibrium used with genotypic data when the phase of double heterozygotes cannot be determined. These bounds are used to standardize the composite measure in the same way used for D', the standardized gametic measure of linkage disequilibrium. Standardization produces a me...

To determine the recurrence rate of gestational diabetes (GDM) during a subsequent pregnancy among women who had GDM during an index pregnancy and to identify factors associated with the probability of recurrence A retrospective longitudinal study was performed in Nova Scotia, Canada, of women who were diagnosed as having GDM during a pregnancy bet...

Raw estimates of disease rates over a geographical region are frequently quite variable, even though one may reasonably expect adjacent communities to have similar true rates. Smoother estimates are obtained by incorporating a penalty into a multinomial likelihood estimation procedure. For each pair of locations, this penalty increases with the dif...

The authors derive the joint distributions of a studentized deleted residual and various regression quantities, calculated with all the data or with one case deleted. They show that the correlation between the studentized deleted residual and the deleted test statistic has an interesting interpretation in terms of well-known regression quantities....

To describe and evaluate a new statistical technique for detecting topographic changes in the optic disc and peripapillary retina measured with confocal scanning laser tomography. The 256x256-pixel array of topographic height values obtained with each image from the Heidelberg Retina Tomograph (Heidelberg Engineering, Heidelberg, Germany) was divid...

Maximum likelihood methods are used to estimate the birth prevalence, the age-at-diagnosis distribution, and the number of infants born with CF in Nova Scotia over a 20 year period. The data were taken from a registry of CF cases, and, because of the delayed onset of symptoms, some CF affected individuals were not diagnosed by the end of the study...

The question of how to handle outliers in data sets has been the subject of heated debate for several centuries. In a regression setting there is the added difficulty that the observation can be outlying in terms of the response variable or the explanatory variables. Various approaches have been used to deal with this, from rejection of the outlyin...

The minimum variance unbiased estimator of the proportion lying outside an m-dimensional rectangle for multivariate normal populations was derived by Baillie (1987a, b). The estimator is a natural extension of a univariate estimator widely used in acceptance sampling. Computation of the multivariate estimator is nontrivial; one must integrate a mul...

Maximum likelihood (ML) and minimum variance unbiased (MVU) estimators of the proportion nonconforming in univariate and bivariate normal random samples are compared for the case where the moments of the distribution are assumed to be unknown and each variable has lower and upper specification limits. Both types of estimator have skewed distributio...

SUMMARY The theoretical principles and practical implementation of a new method for multivariate data analysis, maximum likelihood principal component analysis (MLPCA), are described. MLCPA is an analog to principal component analysis (PCA) that incorporates information about measurement errors to develop PCA models that are optimal in a maximum li...

Regression and principal components analysis (PCA) are two of the most widely used techniques in chemometrics. In this paper, these methods are compared by considering their application to linear, two-dimensional data sets with a zero intercept. The need for accommodating measurement errors with these methods is addressed and various techniques to...

Behavioral and evolutionary ecologists often attempt to quantify monopolization of mates or food items using indices such as the variance, the coefficient of variation (CV), the coefficient of dispersion (CD), or the opportunity for selection (I). Because of the tendency for the variance to increase with the mean and because of the relationship bet...

Purpose. To assess the effect of spatial correlation of topography values on the ability to detect change. Methods. Tests for differences between the baseline and follow-up images obtained with the Heidelberg Retina Tomograph were carried out on each non-overlapping condensed pixel. The image matrix contained 64 x 64 condensed pixels (each condense...

Behavioral and evolutionary ecologists often attempt to quantify monopolization of mates or food items using indices such as the variance, the coefficient of variation (CV), the coefficient of dispersion (CD), or the opportunity for selection (I). Because of the tendency for the variance to increase with the mean and because of the relationship bet...

We investigate acceptance-sampling methods for univariate and multivariate normal data in which the quality of the process relative to specification limits is measured by an estimate of the proportion nonconforming, and the mean and variance are unknown. A maximum likelihood method is developed, and we compare it with existing approaches to accepta...

Many of the people in Maritime Canada can trace their ancestry to some of the oldest settlements in North America. Consequently, both founder effect and genetic drift can be shown to account for the high frequency of some genetic disorders and virtual absence of others. The birth prevalence rate for cystic fibrosis (CF) in Maritime Canada is simila...

Acceptance sampling techniques are used to monitor the accuracy of gas meters. Random samples of meters are taken from homogeneous lots, and two accuracy measurements are recorded for each meter. In the past, the two measurements were averaged, and an acceptance sampling test applied to the sample of averages. In 1987, the plan was modified so that...

The effect of vitamin D supplementation on inorganic sulfate metabolism was examined in very low birth weight (less than 1,500 g) infants at biweekly intervals after birth until 6 weeks of postnatal age. Baseline serum sulfate concentrations were significantly higher in all infants (471 +/- 24 mumol/l, n = 80) than in adults (299 +/- 25 mumol/l, n...

To test the hypothesis that high-dose vitamin D2 supplementation would result in a lower incidence of radiographically detectable bone disease, we randomly assigned 40 very low birth weight infants to a control group who received vitamin D2 in a dosage of 400 IU/day and 41 to an experimental group who received a dosage of 2000 IU/day. After 6 weeks...

Multiplicative correction factors are derived for the limiting F distributions of two test statistics for parameter subsets in nonlinear regression. The factors depend on the first and second derivatives of the model and are related to measures of intrinsic nonlinearity. An example is given for which the correction is substantial. A similar factor...

An extreme example of regression on two variables is presented in which there is almost no correlation between y and x1 and y and x2, yet the coefficient of determination is 1. This example illustrates the often counter-intuitive nature of multivariate relationships and is also relevant to discussions on multicollinearity and variable selection tec...

Confidence regions for some of the parameters in nonlinear regression models are often based on the large sample distribution of the least squares estimator, or equivalently a linear approximation to the model. These regions have a simple ellipsoidal shape but their nominal level is often misleading. Confidence regions based on the likelihood ratio...

Confidence regions for some of the parameters in nonlinear regression models are often based on the large sample distribution of the least squares estimator, or equivalently a linear approximation to the model. These regions have a simple ellipsoidal shape but their nominal level is often misleading. Confidence regions based on the likelihood ratio...

The potential toxicity of vitamin D, alpha-calcidol [1 alpha(OH)D3], and calcitriol [1,25(OH)2D3] was studied by administration of these compounds at three different doses to weanling C57BL/6J mice over a 4-week period. Drug effects on calcium were monitored by serum calcium and urine calcium/creatinine ratio determinations. Tests of renal function...

D-optimal experimental designs for precise estimation in nonlinear regression models are obtained by minimizing the determinant of the approximate variance–covariance matrix of the parameter estimates. This determinant may not give a true indication of the volume of a joint inference region for the parameters, however, because of intrinsic and para...

Joint confidence and likelihood regions for the parameters in nonlinear regression models can be defined using the geometric concepts of sample space and solution locus. Using a quadratic approximation to the solution locus, instead of the usual linear approximation, it is shown that these inference regions correspond to ellipsoids on the tangent p...

A self-modeling procedure was used to develop a template g(z) from the serial creatine kinase (CK) release in 32 patients with acute myocardial infarction. An additional 16 patients were used as an extrinsic test of the template model. For a given patient the fitted CK curve γ(t) is related to the template g(z) by the expression γ(t) = β 1g (t-β 2/...

A simple approach to understanding the behaviour of the partial autocorrelation function of seasonal time series is presented, based on a partial autocorrelation pattern. This pattern, which acts as a signature of the regular component of the model, is a simple composite of the autocorrelation and partial autocorrelation functions of the regular co...

A simple approach to understanding the behaviour of the partial autocorrelation function of seasonal time series is presented, based on a partial autocorrelation pattern. This pattern, which acts as a signature of the regular component of the model, is a simple composite of the autocorrelation and partial autocorrelation functions of the regular co...