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Biomedical subjects

C S Davis

Publications and source records attributed to C S Davis.

At least 55 records · Page 3Linked to original sources
PubMed1993

Acute and late reactions to radiation therapy in patients with collagen vascular diseases.

BACKGROUND: A commonly held belief is that patients with collagen vascular diseases (CVD) have a greater risk of radiation therapy complications than patients without CVD. This impression is based on anecdotal reports, however. METHODS: A group of 61 patients with CVD were compared with a matched control group of 61 patients without CVD. The CVD group included 39 patients with rheumatoid arthritis (RA), 13 with systemic lupus erythematosus (SLE), 4 with systemic sclerosis (scleroderma) (SSc), 4 with dermatomyositis, and 1 with polymyositis. The control group was matched with respect to age, sex, tumor site and histologic characteristics, treatment aim, general treatment method, radiation therapy technique, site irradiated, radiation dose, date of treatment, and follow-up. RESULTS: Overall, there was no significant difference between the CVD and control groups in terms of acute (11% versus 7%, respectively) or late complications (10% versus 7%, respectively). This was also true when only patients who were treated definitively were considered. Furthermore, none of the patients treated palliatively had complications. Three patients in the CVD group had fatal complications, compared with none in the control group. RA was associated with a slight increase in late complications in the definitively treated patients, whereas SLE was associated with a slight increase in acute reactions. No significant acute or late reactions were observed in the patients with SSc, dermatomyositis, or polymyositis. CONCLUSIONS: In general, these differences are less than expected and not statistically significant. Consequently, from these data, the authors could not show a significant increase in radiation therapy complications for patients with CVD.

Adult↗
PubMed1993

A computer program for regression analysis of repeated measures using generalized estimating equations.

RMGEE is an easy-to-use FORTRAN program for the analysis of repeated binary, count, and normally-distributed response variables using the generalized estimating equations approach of Liang and Zeger [1]. The program can be used when measurements are obtained at multiple time points from each subject or experimental unit, and also when the basic sampling unit is a group or cluster of subjects, and the response variable of interest is obtained from each subject within the cluster. It is not necessary for the number of repeated measurements to be the same for every experimental unit and missing data are easily accommodated. Both time-independent (cluster-specific) and time-dependent (occasion- or subject-specific) covariates are permitted. The program can be run on microcomputers, workstations, and mainframe computers. Three examples illustrating the usage and features of RMGEE are provided.

Algorithms↗
PubMed1993

Effect of antipsychotic withdrawal on extrapyramidal symptoms: statistical methods for analyzing single-sample repeated-measures data.

Using symptom severity ratings of extrapyramidal side effects (EPS) during a 4-week antipsychotic washout period, we illustrate particular problems associated with repeated measures of symptom severity and demonstrate four analysis methods. The often suggested analysis of variance and multivariate analysis of variance found no mean change in weekly Simpson Angus scores over the 4-week washout despite the fact that 43% had clinically significant EPS prior to drug discontinuation. On the other hand, the Friedman Analysis of Ranks and Cochran-Mantel-Haenszel (CMH) statistics found significant change over the washout period. These two less well-known techniques place fewer restrictions on the data, can be more sensitive to patterns of change, and may be more appropriate for psychiatric data. The CMH method is particularly attractive since it does not require complete data on all subjects as do many other techniques. This minimizes the number of cases lost to missing data and increases the generality of the results.

Adult↗
PubMed1993

The analysis of longitudinal polytomous data: generalized estimating equations and connections with weighted least squares.

In recent years, methods have been developed for modelling repeated observations of a categorical response obtained over time on the same individual. Although situations in which the repeated response is binary or Poisson have been studied extensively, relatively little attention has been given to polytomous categorical response variable. In this paper, we extend the estimating equations initially developed for clustered discrete data by Liang and Zeger (1986, Biometrika 73, 13-22), and subsequently extended by Prentice (1988, Biometrics 44, 1033-1048), to polytomous response variables. Under certain assumptions, we illustrate that these estimating equations simplify to the weighted least squares (WLS) equations formalized by Koch et al. (1977, Biometrics 33, 133-158). This connection provides a formal framework for obtaining iterated weighted least squares model parameter estimates. Cumulative logit models are developed and applied to a representative longitudinal data set. Simulation results comparing WLS, an iterative form of WLS, and independence estimating equations using a robust estimate of the variance are presented.

Analysis of Variance↗
PubMed1993

A test of the missing data mechanism for repeated categorical data.

Due to the occurrence of missing observations, longitudinal data are rarely balanced and complete. Weighted least squares analyses described by Grizzle, Starmer, and Koch (1969, Biometrics 25, 489-504) have been developed for the analysis of incomplete longitudinal categorical data [Stanish, Gillings, and Koch (1978, Biometrics 34, 305-317); Woolson and Clarke (1984, Journal of the Royal Statistical Society, Series A 147, 87-99)]. However, all these analyses have assumed that missing observations are missing completely at random in the sense of Rubin (1976, Biometrika 63, 581-592). When the occurrence of missing observations is related to the unobserved response values, these analyses may result in biased results. In this paper, we develop a simple and practical test of the missing mechanism in incomplete repeated categorical data. The proposed test is an extension of the test of Little (1988, Journal of the American Statistical Association 83, 1198-1202) and uses a test criterion given in general form by Wald. The test is illustrated using data from a longitudinal investigation of obesity in school-age children.

Adolescent↗
PubMed1992

A double-blind, placebo-controlled multicenter study of tacrine for Alzheimer's disease. The Tacrine Collaborative Study Group.

BACKGROUND: In Alzheimer's disease, there is a marked decline in the function of cholinergic neurons in the brain. However, studies of treatment with cholinesterase inhibitors have produced conflicting results. We conducted a multicenter trial to evaluate whether the cholinesterase inhibitor tacrine (1,2,3,4-tetrahydro-9-acridinamine monohydrochloride monohydrate) could improve cognition in patients with Alzheimer's disease. METHODS: Of 632 eligible patients with probable Alzheimer's disease, 215 improved while receiving tacrine during a preliminary crossover phase to determine responsiveness and the best dose. The 215 patients were randomly assigned to receive either placebo or their best dose of tacrine (10 or 20 mg four times a day) in a six-week, double-blind trial. The primary measures of efficacy were the cognitive subscale of the Alzheimer's Disease Assessment Scale and the Clinical Global Impression of Change scale; the secondary measures included the Mini-Mental State Examination and the assessment of the activities of daily living. RESULTS: At the end of the six-week trial, the patients receiving tacrine had a mean adjusted cognitive-subscale score of 30.3 (Alzheimer's Disease Assessment Scale) as compared with 32.7 in patients receiving placebo. This represents a smaller decline (by 2.4 points) in cognitive performance in the tacrine group (P < 0.001). There were no differences between the groups in their global-rating scores. The tacrine group had a significantly smaller decline in the activities of daily living. The results of the Mini-Mental State Examination favored tacrine, but the differences were small and not statistically significant (a score of 16.0 with tacrine vs. 15.3 with placebo; P = 0.08). Gastrointestinal symptoms, elevation of aminotransferase levels, and headache were the most frequent side effects; all could be reversed by reducing the dose or discontinuing treatment. CONCLUSIONS: In this short-term study in patients with Alzheimer's disease who were selected for apparent responsiveness to tacrine, treatment with tacrine resulted in a statistically significant reduction in the decline of cognitive function, although this reduction was not large enough to be detected by the study physicians' global assessments of the patients.

Activities of Daily Living↗
PubMed1991

A one degree of freedom nominal association model for testing independence in two-way contingency tables.

In testing the independence of the row and column variables in a two-way contingency table, the standard Pearson and likelihood ratio chi-square statistics often have low power, especially as the dimensions of the table increase. In this paper, one degree of freedom tests of independence based on likelihood ratio and score statistics from an association model for tables with nominal row and column classifications are described. The score statistic is especially easy to use, since it can be expressed in closed form, is simple to compute, and has size and power properties which are only slightly inferior to those of the more complicated likelihood ratio statistic.

Brain Neoplasms↗
PubMed1991

Semi-parametric and non-parametric methods for the analysis of repeated measurements with applications to clinical trials.

Techniques applicable for the analysis of longitudinal data when the response variable is non-normal are not nearly as comprehensive as for normally-distributed outcomes. However, there have been several recent developments. Semi-parametric and non-parametric methodology for the analysis of repeated measurements is reviewed. The commonly encountered design in which, for each subject, one assesses a univariate response variable at multiple fixed time points, is considered. The types of outcomes considered include binary, ordered categorical, and continuous (but extremely non-normal) response variables. All of the methods considered allow for incomplete data due to the occurrence of missing observations. In addition, discrete and/or continuous covariates, which may be time-dependent, are accommodated by some of the approaches. The methods are demonstrated using data from three clinical trials.

Clinical Trials as Topic↗
PubMed1991

Parrot psychology and behavior problems.

Behavior modification training, like veterinary medicine, is an exacting science, requiring a knowledge of not only wild avian behavior, but of child and adult human behavior as well. It is important to note that absolutely any changes in a bird's or its owner's environment may trigger a vast assortment undesirable behaviors. Some behavior problems are simple, but most have multiple causes and each of those causes must be determined and corrected before a high rate of success is evident. As in veterinary medicine, some birds respond to general "shotgun" techniques; however, parrots are intelligent and complex creatures. They consider themselves an integral part of their human "flock" and respond as such. Most commonly seen negative behaviors can be altered, at least to some extent, and, in most cases, they can be alleviated completely. Yelling at the bird, striking it, or any other type of confrontational behavior modification technique is virtually useless and can actually worsen most situations. A high percentage of success involves extensive history taking, an understanding of human and wild animal flock behavior, and the time to create a complete program for each individual and its owner.

Animals↗
PubMed1991

A model of lifetime osteoporosis impact.

The study goal was to use population-based data to model aspects of lifetime osteoporosis impact not previously studied, specifically: (1) to estimate person-years of fracture-related functional impairment against the trajectory of functional status in the general population; (2) jointly to consider hip, vertebral, and Colles' fractures in estimating the percent of women who will ever fracture; and (3) to estimate the lifetime number of fractures expected in a cohort of 10,000 50-year-old white postmenopausal women. The model estimates that 54% of 50-year-old women will sustain osteoporosis-related fractures during their remaining lifetimes. Beyond the functional impairment expected in similarly aged, unfractured women, osteoporosis-related fractures are estimated to cause 6.7% of women to become dependent in basic activities of daily living; 7.8% are expected to require nursing home care for an average of 7.6 years.

Cohort Studies↗
PubMed1988

Secular trends in body mass in the United States, 1960-1980.

Data from four National Health Examination Surveys conducted of the US population from 1960 to 1980 were analyzed to determine secular trends in obesity for white and for black adolescents and young adults of both sexes. Body mass index was categorized into four levels using cut points determined by the 50th, 75th, and 85th percentiles at the first survey in 1960-1962. The weighted proportions of persons in these body mass categories were determined, and statistical models were developed to describe secular trend and race effects. No consistent secular trends were found for white or black youths aged 12-17 years. No significant secular trends in obesity were found for white or black young males aged 18-34 years. Both for white and for black adult females, there were significant secular increases in the proportion of adult females in each of the successively heavier categories of body mass index. These increases were identical for white and for black adult females on the log-odds scale, but black adult females were already significantly heavier at the first survey. This race effect persisted throughout the entire time interval.

Adolescent↗
PubMed1988

Treatment of the elderly brain-injured patient. Experience in a traumatic brain injury unit.

Recovery from traumatic brain injury in the elderly is a subject rarely discussed in the medical literature, and existing data is conflicting. The Traumatic Brain Injury Unit at Gaylord Hospital routinely admits patients over 50 years of age for rehabilitation after significant closed head injury. Of the 26 elderly head-injured patients reviewed over a four-year period for this study, 85% eventually returned to a home setting, with more than half independent in activities of daily living. Based on this encouraging data, it is suggested that the older head-injured patient can recover from severe closed head injury.

Activities of Daily Living↗
PubMed1988

Reticular erythematous mucinosis and thrombocytopenic purpura. Report of a case and review of the world literature, including plaquelike cutaneous mucinosis.

A case of reticular erythematous mucinosis associated with chronic idiopathic thrombocytopenic purpura and circulating immune complexes is described. We compare reticular erythematous mucinosis with the similar plaquelike cutaneous mucinosis. We discuss the apparent photosensitivity of reticular erythematous mucinosis and its possible relationship with altered states of immune function such as diabetes, thyroid disease, and neoplasia. The somewhat varied but characteristic histopathologic findings and staining are reviewed, including the characteristic perivascular and occasional perifollicular lymphocytic infiltrate and Alcian blue-positive dermal mucin. Treatment with antimalarial drugs still appears to be the most uniformly successful therapeutic approach to the management of this chronic dermatosis. Further research efforts should be directed at understanding its link with altered states of immune function.

Aged↗
PubMed1988

Nonparametric methods for analyzing incomplete nondecreasing repeated measurements.

In comparing the effectiveness of two treatments, suppose that nondecreasing repeated measurements of the same characteristic are scheduled to be taken over a common set of time points for each study subject. A class of univariate one-sided global asymptotically distribution-free tests is proposed to test the equality of the two treatments. The test procedures allow different patterns of missing observations in the two groups to be compared, although the missing data mechanism is required to be independent of the observations in each treatment group. Test-based point and interval estimators of the global treatment difference are given. Multiple inference procedures are also provided to examine the time trend of treatment differences over the entire study. The proposed methods are illustrated by an example from a bladder cancer study.

Biometry↗
PubMed1987

Kinetics of heat inactivation of phenyl valerate hydrolases from hen and rat brain.

Heat inactivation was studied at 45, 50, 55, and 60 degrees for all of the phenyl valerate hydrolases (PVase), including neurotoxic esterase (NTE) and inhibitor-resistant esterase (IRE), in homogenates of hen or rat brain or in preparations of hen brain microsomal membranes. Hen and rat brain homogenates were prepared in buffer (50 mM Tris/0.20 mM EDTA, pH 8.00, at 25 degrees). Hen brain microsomes were suspended either in buffer or in aqueous dimethyl sulfoxide (DMSO, 40%, w/v), or solubilized either in aqueous Triton X-100 (0.10%, w/v) or in 40% (w/v) DMSO. Enzyme activities were measured at 37 degrees using phenyl valerate as substrate. Each enzyme activity in all of the preparations exhibited biphasic heat inactivation kinetics. Apparent rate constants were calculated for the fast (kf) and slow (ks) reactions, along with the relative amounts of activity in each component (Af, As) expressed as percentages of the total activity. For a given preparation and temperature, respective values of kf or ks were similar for PVase, NTE, and IRE, with a mean kf/ks ratio of 52 across all preparations. Af and As were a function of temperature. Mean values of the apparent activation energies (Ea) for all activities and preparations were 44 and 25 kcal/mol for the fast and slow inactivation reactions respectively. These results indicate that all phenyl valerate hydrolases in hen and rat brain undergo a common heat-induced structural change leading to loss of enzymic activity.

Animals↗