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PubMed1997

Mantel-Haenszel test statistics for correlated binary data.

This paper proposes two new Mantel-Haenszel test statistics for correlated binary data in 2 x 2 tables that are asymptotically valid in both sparse data (many strata) and large-strata limiting models. Monte Carlo experiments show that the statistics compare favorably to previously proposed test statistics, especially for 5-25 small to moderate-sized strata. Confidence intervals are also obtained and compared to those from the test of Liang (1985, Biometrika 72, 678-682).

Biometry↗

PubMed2005

Regression analysis of overdispersed correlated count data with subject specific covariates.

A robust likelihood approach for the analysis of overdispersed correlated count data that takes into account cluster varying covariates is proposed. We emphasise two characteristics of the proposed method: That the correlation structure satisfies the constraints on the second moments and that the estimation of the correlation structure guarantees consistent estimates of the regression coefficients. In addition we extend the mean specification to include within- and between-cluster effects. The method is illustrated through the analysis of data from two studies. In the first study, cross-sectional count data from a randomised controlled trial are analysed to evaluate the efficacy of a communication skills training programme. The second study involves longitudinal count data which represent counts of damaged hand joints in patients with psoriatic arthritis. Motivated by this study, we generalize our model to accommodate for a subpopulation of patients who are not susceptible to the development of damaged hand joints.

Arthritis, Psoriatic↗

PubMed1992

An annotated bibliography of methods for analysing correlated categorical data.

This paper provides an annotated bibliography of over 100 articles concerning methods for analysing correlated categorical response data. Most of the papers listed here concern categorical regression models and estimation, with particular emphasis on binary responses. The papers are classified by several characteristics which group them according to common themes. The bibliography serves as a reference of methods for analysts of correlated categorical data, as well as for persons interested in methodologic work in this active area of statistical research.

Clinical Trials as Topic↗

PubMed1994

Tests for trend in developmental toxicity experiments with correlated binary data.

In this article, the operating characteristics of recently proposed tests for trend in correlated binary data arising in laboratory studies of developmental toxicity are examined using both computer-generated and experimental data. Specifically, we consider adjusted Cochran-Armitge tests based on the Rao-Scott transformation which are of the same general form as that for uncorrelated data. In addition, generalized score tests based on generalized estimating equations allowing for extrabinomial variation in the data are discussed. Specific forms of these statistics demonstrating favorable type I and type II error rates are identified and recommended for use in practice. The application of these tests is illustrated using data from studies of developmental toxicity that have been reported in the literature.

Abnormalities, Drug-Induced↗

PubMed1988

Ontario Child Health Study: patterns of ambulatory medical care utilization and their correlates.

Data from a large epidemiologic survey of Ontario children 4 to 16 years of age are presented concerning the frequency and correlates the use of ambulatory medical care services during a 6-month period in which a universal, first-dollar health insurance plan was used. Patterns of use of ambulatory medical care are described for three settings: doctor's offices, emergency rooms, and hospital outpatient departments. A group of children who are frequent users of ambulatory medical care (defined as using three or more services in 6 months) consumed nearly two thirds of all services. Two regression equations are presented--one predicting use/nonuse of ambulatory medical care and the other predicting the total number of visits for medical care. Although only a small proportion of the variance in use/nonuse and amount of use was explained, the major determinant of both ambulatory medical care use and frequency of use was the child's physical health status as perceived by the parent. Younger child, urban area of residence, the number of chronic medical problems of the child, and higher level of maternal education also contributed to the explanation of use v nonuse. Among ambulatory medical care users, high users were more likely to be described as having mental health problems and have parents who had been treated for "nerves." Family size and socioeconomic variables were not important factors in use, suggesting that universal health insurance reduces some barriers to ambulatory medical care for children.

Adolescent↗

PubMed1999

Comment on "manic-depressiveness and its correlates".

Data from a sample of 612 college students showed that the Depression subscale of the Manic-Depressiveness Scale had greater internal reliability than the Mania subscale. Furthermore, correlates of the total scale score did not appear to provide as useful information as use of the Depression and Mania subscales separately.

Adult↗

PubMed1986

Smoking, drinking and use of illicit drugs among adolescents in Ontario: prevalence, patterns of use and sociodemographic correlates.

Data from a cross-sectional survey of the health of Ontario children carried out in 1983 were used to provide estimates of the prevalence, patterns and sociodemographic correlates of the use of tobacco, alcohol and illicit drugs (substance use) among adolescents aged 12 to 16 years. Ninety-one percent of selected households participated. The prevalence rates of all categories of substance use, except use of inhalants, increased with increasing age. Among children aged 14 to 16 years the rates for girls were higher than those for boys for all categories of substance use except use of other, nondefined drugs. The prevalence rates of substance use tended to be higher in small urban areas except for use of marijuana (more prevalent in large urban areas) and use of inhalants (more prevalent in rural areas). The strongest evidence of clustering of substance use within families was found for smoking. Children who used less prevalent drugs (e.g., "hard" drugs) also tended to use the more prevalent ones (e.g., marijuana, tobacco and alcohol). Associations between substance use and low socioeconomic status suggested a positive relation with smoking and a negative relation with use of alcohol. The findings highlight the need for preventive programs aimed at specific subgroups in the adolescent population.

Adolescent↗

PubMed1992

Children's physical activity: an exploratory study of psychological correlates.

Data are now accumulating that show that some children have apparently low levels of habitual physical activity, as measured by heart rate telemetry. However, relatively little is known about the likely correlates or determinants of such activity patterns. The purpose of this study, therefore, was to explore the extent to which activity levels were related to selected psychological factors. The heart rates of 11/12-year old boys and girls (N = 72) were monitored continuously for 12 hr on each of three school days. The same subjects completed psychological inventories assessing physical self-perceptions and motivation. Intrinsic motivation towards physical education and sport was significantly correlated with activity levels for boys. Motivational orientations also predicted activity, but differently for boys and girls. Evidence was found for a discrimination between 'active' and 'less active' girls on the basis of their physical self-perception and motivation scores.

Body Image↗

PubMed1984

A family study of anthropometric traits in a Punjabi community: I. Introduction and familial correlations.

Data on 40 anthropometric measurements from 144 nuclear families in Chandigarh, India, are presented. Most families contain a pair of monozygotic or dizygotic twins, one or more singleton siblings, and their parents. Familial correlations for age-sex standardized, normalized measurements are estimated by maximum likelihood for marital, parent-child, sibling, and twin pairs. Heterogeneity tests for sex-specific subtype correlations male-male, male-female, female-female) indicate that the sex of the relative plays no significant role in the magnitude of the familial correlations except for maternal effects and differences among male and female twin pairs for a few of the variables. Marital correlations are high for body measurements, but not for head or face variables. Twin correlations seem to indicate a higher level of heritability than correlations from other family members.

Adolescent↗

PubMed1975

Liquid ion exchangers in paper chromatography of steoidal glucosiduronic acids. Influence of different exchangers on the mobility in chloroform-formamide and correlation of chromatographic data.

A group of 25 steroidal glucosiduronic acids was chromatographed on paper chloroform-formamide in the presence of several different liquid ion exchangers. Chromatograms were run also in three Bush-type systems. RF values were converted into RM values and the data were correlated by use of a series of regression equations of the type RM(Y) = a-RM(X) + b, in which X designates a standard system to which each other system (Y) is compared. The ratio of the slope a to the correlation coefficient r (i.e., a/r) is a measure of the resolving power of system Y relative to the standard system; intercept b, in association with slope a, is an indication of the polarity of system Y relative to X. The correlation coefficient r and the standard error of estimate sy-x are indications of whether solvent systems Y and X have very similar or relatively different resolving properties for a group of solutes. The regression equations are useful for correlating chromatographic data obtained from a group of compounds in several solvent systems. Properties of the chromatography systems are discussed and the relative importance of ion exchange and hydrogen bonding with the various solvent systems is pointed out. Delta RMg and delta RMr values are given for functional groups at several locations in the conjugates for ten of the chromatography systems.

Chloroform↗

PubMed1986

Transmissible and nontransmissible components of anthropometric variation in the Alexanderwohl Mennonites: I. Description and familial correlations.

Data on 34 anthropometric measures from the Alexanderwohl Mennonite congregations of Kansas and Nebraska are presented. A factor analysis of these traits shows that body length and body width measures are distinct from each other as well as from measures of the head and face. Moreover, familial correlations estimated by maximum likelihood for all 34 traits tend to separate from each other along factor lines with correlations for body lengths being the highest and those for skinfolds and circumferences being the lowest. These results suggest the presence of various body "fields" which are under differing degrees of genetic and environmental control. We offer the term "functional multifactorial complex" as a means of referring to the joint genetic and environmental influences on these fields.

Anthropometry↗

PubMed1995

Comparison of two approaches to analyzing correlated binary data in developmental toxicity studies.

Recently developed statistical methodology is presented for analyzing correlated developmental toxicity data where multiple measures are obtained on individual units such as rat pups. Of particular interest is the assessment of the homogeneity of effects from chemical exposure across different outcomes such as malformation types or non-ossification of forepaw digits. Such contrasts are referred to as within-cluster effects, as they represent differences between observations within a cluster (e.g., pup). Between-cluster effects correspond to comparison of observations from different clusters, e.g., pups exposed to varied doses of chemicals or carcinogens. Two classes of statistical models are available for estimation of these distinct types of effects: (1) cluster-specific models in which regression adjustments are made for cluster effects, and hence all parameters are interpreted as within-cluster effects; and (2) population-averaged models in which no explicit adjustments are made for cluster, and thus all parameters are interpreted as group differences without regard to whether they represent between- or within-cluster effects. Many models in the developmental toxicity literature are population-averaged logistic regression models ignoring variation among clusters which may be significant under strong influences of genetic and environmental factors. Under such conditions, confidence interval-based inference for effect homogeneity will depend upon the class of models. These issues are illustrated with data from two developmental toxicity studies: (1) a National Toxicology Program study of the effects of in utero exposure to di(2ethylhexyl)phthalate among three malformation outcomes in mouse pups; and (2) a study conducted by Hartsfield to investigate the effects of anticonvulsant phenytoin on the risk of non-ossification among digits of the left and right forepaws in rat pups.

Abnormalities, Drug-Induced↗

PubMed1993

Early detection of Alzheimer's disease: a statistical approach using positron emission tomographic data.

Correlational analysis of regional cerebral glucose metabolism (rCMRglc) obtained by high-resolution positron emission tomography (PET) has demonstrated reduced neocortical rCMRglc interactions in mildly/moderately demented patients with probable Alzheimer's disease (AD). Thus, identification of individual differences in patterns of rCMRglc interactions may be important for the early detection of AD, particularly among individuals at greater risk for developing AD (e.g., those with a family history of AD). Recently, a statistical procedure, using multiple regression and discriminant analysis, was developed to assess individual differences in patterns of rCMRglc interdependencies. We applied this new statistical procedure to resting rCMRglc PET data from mildly/moderately demented patients with probable AD and age/sex-matched controls. The aims of the study were to identify a discriminant function that would (a) distinguish patients from controls and (b) identify an AD pattern in an individual at risk for AD with isolated memory impairment whose initial PET scan showed minor abnormalities, but whose second scan showed parietal hypometabolism, coincident with further cognitive decline. Two discriminant functions, reflecting interactions involving regions most involved in reduced correlations in probable AD, correctly classified 87% of the patients and controls, and successfully identified the first scan of the at-risk individual as AD (probability > 0.70). The results suggest that this statistical approach may be useful for the early detection of AD.

Aged↗

PubMed2007

Interval estimation for rank correlation coefficients based on the probit transformation with extension to measurement error correction of correlated ranked data.

The Spearman (rho(s)) and Kendall (tau) rank correlation coefficient are routinely used as measures of association between non-normally distributed random variables. However, confidence limits for rho(s) are only available under the assumption of bivariate normality and for tau under the assumption of asymptotic normality of tau. In this paper, we introduce another approach for obtaining confidence limits for rho(s) or tau based on the arcsin transformation of sample probit score correlations. This approach is shown to be applicable for an arbitrary bivariate distribution. The arcsin-based estimators for rho(s) and tau (denoted by rho(s,a), tau(a)) are shown to have asymptotic relative efficiency (ARE) of 9/pi2 compared with the usual estimators rho(s) and tau when rho(s) and tau are, respectively, 0. In some nutritional applications, the Spearman rank correlation between nutrient intake as assessed by a reference instrument versus nutrient intake as assessed by a surrogate instrument is used as a measure of validity of the surrogate instrument. However, if only a single replicate (or a few replicates) are available for the reference instrument, then the estimated Spearman rank correlation will be downwardly biased due to measurement error. In this paper, we use the probit transformation as a tool for specifying an ANOVA-type model for replicate ranked data resulting in a point and interval estimate of a measurement error corrected rank correlation. This extends previous work by Rosner and Willett for obtaining point and interval estimates of measurement error corrected Pearson correlations.

Confidence Intervals↗

PubMed2005

Changing definition of productive life in US Holsteins: effect on genetic correlations.

Data included 392,800 records for cows born between 1995 and 1997. Traits analyzed were milk, fat, and protein yields, somatic cell score, days open (DO), 18 linear type traits, final score, and several measures of longevity. Productive life (PL) was defined as the total number of days in milk up to 84 mo of age with a restriction of 305, 500, or 999 d per lactation (PL(305), PL(500), or PL(999), respectively). Herd life was defined as the total number of days from the first calving date to the last (culling) date. A multiple-trait sire model including the effects of registration status, herd-year, age group, month of calving and stage of lactation, sire, and residual was used for parameter estimation. The average duration of the first lactation was 365 d for survivors and 386 d for culled cows. Lactation lengths for the survivors in the next 3 parities all exceeded 330 d. Heritability estimates of between 0.08 and 0.10 were obtained for all definitions of longevity. As maximum recordable PL was increased from 305 to 999 d per lactation, the genetic correlations with milk production increased (from -0.11 to +0.14) and with DO decreased (-0.62 to -0.27). Formulas for an indirect prediction of PL from correlated traits were developed. As maximum PL per lactation was increased, little change in the weights used to predict the various measures of PL, with the exception of DO was found. As the currently used value of PL(305) does not properly account for the longer lactation lengths that are routinely occurring with today's cows, PL with longer lactations may be preferable in routine evaluation.

Animals↗

PubMed1975

Sjöbring personality dimensions: norms for some American populations.

An American version of the MNT Inventory (Sjöbring personality dimensions) was administered to three separate groups of American subjects. Normative data on the Sjöbring dimensions, including correlational data between the dimensions, was reported for these groups and compared to published normative data from prior studies in Sweden and in the United Kingdom. For the American groups, the correlations between dimensions were negligible or very small, in accord with Sjöbring theory. There were similar patterns to the scale scores and to the correlational data for the American groups and comparable Swedish groups. The results suggest that the American version of the MNT inventory is a valid tool for obtaining Sjöbring dimension scores on American subjects.

Adolescent↗

PubMed1985

Insomnia and its treatment. Prevalence and correlates.

Data for this report come from a nationally representative probability sample survey of noninstitutionalized adults, aged 18 to 79 years. The survey, conducted in 1979, found that insomnia afflicts 35% of all adults during the course of a year; about half of these persons experience the problem as serious. Those with serious insomnia tend to be women and older, and they are more likely than others to display high levels of psychic distress and somatic anxiety, symptoms resembling major depression, and multiple health problems. During the year prior to the survey, 2.6% of adults had used a medically prescribed hypnotic. Typically, use occurred on brief occasions, one or two days at a time, or for short durations of regular use lasting less than two weeks. The survey also found a small group of hypnotic users (11% of all users; 0.3% of all adults) who reported using the medication regularly for a year or longer. If we include anxiolytics and antidepressants, 4.3% of adults had used a medically prescribed psychotherapeutic drug that was prescribed for sleep; 3.1% had used an over-the-counter sleeping pill. The majority of serious insomniacs (85%) were untreated by either prescribed or over-the-counter medications.

Adolescent↗

PubMed2002

[Use of Azopiram for rapid diagnosis of epithelial tumors of the urinary bladder (experimental data)].

Correlation of development of tumor pathology and macro- and microhematuria was investigated in the experiments using 50 male rats with N-butyl-N-(4-hydroxybutyl)-nitrosoamine-induced tumors of the urinary bladder. Our highly-sensitive agent Azopiram was employed to monitor hematuria. Microhematuria, which subsequently developed into macrohematuria as tumor matured and turned malignant, was identified as early as at such incipient neoplastic changes as focal hyperplasia of the urothelium and micropapillomatosis. The test can be used outside clinic as a measure of self-control in recurrent cancer of the urinary bladder.

Aminopyrine↗