PubMed Health⌕ Search

Biomedical subjects

R D Gibbons

Publications and source records attributed to R D Gibbons.

At least 19 recordsLinked to original sources
PubMed1992

An application of item response theory to alexithymia assessment among abstinent alcoholics.

An item response theory (IRT) model identified three dimensions assessed by the Toronto Alexithymia Scale (TAS) in a sample of 130 male applicants for inpatient care at a Veterans Administration (VA) medical center alcoholism treatment program. A unidimensional solution did not capture all of alexithymia's theoretical features. Subjects with lower alexithymia scores gave positive responses to items tapping emotional awareness deficits; only those with higher alexithymia scores gave positive responses to items tapping external, operative cognitive style. Thus, a total TAS score may not represent alexithymia accurately in substance-abusing patient populations.

Adult↗
PubMed1992

Predicting risk for medical malpractice claims using quality-of-care characteristics.

The current fault-based tort system assumes that claims made against physicians are inversely related to the quality of care they provide. In this study we identified physician characteristics associated with elements of medical care that make physicians vulnerable to malpractice claims. A sample of physicians (n = 248) thought to be at high or low risk for claims was surveyed on various personal and professional characteristics. Statistical analysis showed that 9 characteristics predicted risk group. High risk was associated with increased age, surgical specialty, emergency department coverage, increased days away from practice, and the feeling that the litigation climate was "unfair." Low risk was associated with scheduling enough time to talk with patients, answering patients' telephone calls directly, feeling "satisfied" with practice arrangements, and acknowledging greater emotional distress. Prediction was more accurate for physicians in practice 15 years or less. We conclude that a relationship exists between a history of malpractice claims and selected physician characteristics.

Clinical Medicine↗
PubMed1992

The efficacy of psychotropic drugs: implications for power analysis.

The estimation of the correct sample size to successfully test a hypothesis has become critical. A common approach to this problem is for the investigating team to complete a pilot study of a few patients to establish the "active drug-placebo" difference, using this "effect size" to perform the power analysis for sample size estimation. Given the variability evident in the effect size from completed and published studies, the pilot study approach may not be entirely dependable. The authors propose a method to obtain this initial "active drug-placebo" difference, in the field of psychotropic drug research. They apply meta-analysis to statistically summarize effect sizes obtained from an exhaustive review of the literature for a specific psychotropic drug in a given clinical condition. All double-blind, random assignment studies are used to calculate the effect size; therefore, no selection bias exists. These literature-based effect sizes are then used to perform the traditional power analysis for sample size estimation. The authors propose these estimations as a convenient reference source for future clinical investigators.

Humans↗
PubMed1991

Lack of a bimodal distribution of ventricular size in schizophrenia: a Gaussian mixture analysis of 1056 cases and controls.

The finding of clinical and laboratory differences between schizophrenic patients with large and small cerebral ventricles has led to the widespread assumption that large ventricles are a marker that characterizes a subgroup of patients with schizophrenia. We reviewed all published English language ventricle-to-brain ratio (VBR) studies in which individual data points were available (schizophrenics: n = 691, medical controls; n = 205, normal volunteers: n = 160). Using a univariate normal mixture model to examine the distribution of ventricular size in each group, we found no evidence of a mixture of Gaussian distributions (i.e., "bimodality") within any of the three groups. The same analysis was then performed on the combined sample of schizophrenic patients and normal and medical controls, respectively. In each case the improvement in fit of a mixture of normal distributions compared to a single component normal distribution was significant. The data do not support the notion that ventricular enlargement is a discontinuous marker of a subtype of schizophrenia.

Analysis of Variance↗
PubMed1991

Random regression models for multicenter clinical trials data.

A random-effects regression model is proposed for the analysis of data arising from multicenter clinical trials. Advantages of the random regression model (RRM) in this context include that it allows for varying numbers of subjects within the different centers, it can assess the influence of variables measured both at the level of the subject and at the level of the center on the subject's clinical outcome, and it controls for and estimates the amount of intracenter variation that is present in the data. An example utilizing data collected in the National Institute of Mental Health schizophrenia collaborative study, where subjects were clustered within nine centers, illustrates the usefulness of the statistical model. Other applications and extensions of RRM within a psychiatric framework are discussed.

Humans↗
PubMed1990

A statistical method for evaluating suicide clusters and implementing cluster surveillance.

The absence of any standard definition of suicide cluster events hinders understanding of the prevalence of the problem, hinders the development of appropriate public health responses to observed clusters, and ultimately hinders investigation of the mechanisms underlying contagious communication of suicidal behavior. The authors introduce a Poisson mixture model for assessing potential clusters of adolescent suicide, apply that model to the monthly incidence rates of adolescent suicide for one populous US county over the last 11 years, and generate 99% tolerance limits with 95% confidence for the number of suicides which may occur by chance within specific intervals of time in that county. The suicide incidence data showed a remarkable fit to a single Poisson distribution, suggesting it is not unreasonable to consider the cases as randomly-distributed and independent events. The authors conclude that there is no evidence that adolescent suicides occurred in clusters in the place and in the time frame under study, and recommend the Poisson mixture model for ascertaining clusters as well as implementing cluster surveillance.

Adolescent↗
PubMed1989

What is the mechanism by which suicide attempts predispose to later suicide attempts? A mathematical model.

A state dependence model of serial behavior suggests that each occurrence increases the subsequent likelihood of that behavior being repeated. A heterogeneity model, by contrast, suggests that the likelihood of a behavior occurring is predetermined, and uninfluenced by intervening occurrences. We have applied the random-effects probit model of Gibbons and Bock (1987) to examine the fit of the state dependence and heterogeneity models to longitudinal data on suicide attempts by 928 patients with affective disorder. Heterogeneity but not state dependence was required to model these data. The findings suggest that when considering patients with moderate to severe major affective disorder, the clinician should not interpret the absence of any recent suicide attempts to mean that the patient is at relatively low risk for attempting suicide in the future. An implication of the heterogeneity model is that suicide attempts made many years ago may have equal value to recent attempts when estimating an individual's "predisposition" to nonlethal attempts in the future.

Adolescent↗
PubMed1989

Assessment of the debrisoquin and dextromethorphan phenotyping tests by gaussian mixture distributions analysis.

From a sample of 149 unrelated Spaniards, individuals were phenotyped for their ability to hydroxylate debrisoquin and O-demethylate dextromethorphan. The distribution of urinary metabolic ratios for each test was analyzed by univariate gaussian mixture distributions analysis to determine the number of populations, the mean and standard deviation of the metabolic ratios for each population, and the proportion belonging to each population. For the 124 subjects phenotyped with both the debrisoquin and dextromethorphan tests a bivariate analysis was performed. The results demonstrate that both tests similarly separated this sample into two populations, with 10% belonging to poor metabolizer phenotypes. In addition, the correlation between the metabolic ratios from each test is significant, indicating that they are measuring the same biologic trait and the certainty of correctly identifying the debrisoquin oxidation phenotype of an individual is improved by using the results of both tests.

Debrisoquin↗
PubMed1989

Investigating drug plasma levels and clinical response using random regression models.

The reanalysis of the Riesby dataset using a random regression model indicates a significant effect of DMI plasma measurements on HAM-D scores across the four timepoints of the study. This effect is especially strong when the HAM-D change from baseline score is used in place of the actual HAM-D score at the four timepoints. A significant effect of IMI was not found for either the actual HAM-D score or the HAM-D change from baseline score. An endogenous effect was marginally significant when the actual HAM-D score was used; however, this effect was not observed when the HAM-D change score was used as the dependent measure. There also was evidence of a marginally significant effect due to autocorrelation of the residuals, indicating that the residuals at a given timepoint were related to the residuals from previous timepoints according to a first-order autoregressive process. In contrast, when the repeated measures MANOVA was used to analyze these data, a significant effect of DMI was not observed, since subjects without complete data at all timepoints had to be dropped from the analysis. In longitudinal psychiatric studies where missing data are the rule (rather than the exception), the random regression approach provides an attractive alternative to the traditional methods of analyzing longitudinal data.

Humans↗
PubMed1988

Cerebrospinal fluid and urinary biogenic amines in depressed patients and healthy controls.

The National Institute of Mental Health-Clinical Research Branch Collaborative Study investigated 132 drug-free, severely depressed patients and 80 healthy controls. Forty-five percent of the depressed patients excreted markedly elevated levels of urinary epinephrine (E) and metanephrine (MET), while only 5% of healthy controls did so. Using gaussian mixture distributions, we identified two subgroups of depressed patients: one excreting normal levels and the other excreting high levels of urinary E, MET, norepinephrine, and normetanephrine. Cerebrospinal fluid homovanillic acid levels were low in a subgroup of depressed patients. When analyzed by subgroup, the elevated E + MET group had markedly lower cerebrospinal fluid homovanillic acid levels than controls, whereas depressed patients with normal catecholamine levels did not. Since it has been postulated that there are two subgroups of depressed patients, those with low 3-methoxy-4-hydroxyphenylglycol (MHPG) levels and normal 5-hydroxyindoleacetic acid (5-HIAA) levels and those with normal MHPG levels and low 5-HIAA levels, several analyses were performed to see if such a group could be identified. Our analysis failed to find evidence of a subgroup of depressives with low MHPG and normal 5-HIAA levels or normal MHPG and low 5-HIAA levels.

Biogenic Amines↗
PubMed1988

Reducing the number of rabbits in the Draize eye irritancy test: a statistical analysis of 155 studies conducted over 6 years.

The Draize eye irritancy test in rabbits has been the focus of recent efforts to reduce the use of live animals in toxicity testing. A suitable alternative is not yet available; therefore, we studied the adequacy of reducing the number of rabbits used per test. Data generated from 6-rabbit eye irritation tests of 155 various materials were used to determine the ability of irritation scores from all possible combinations of 5-, 4-, 3-, or 2-rabbit subsets to predict the Draize score derived from six rabbits. There are 930, 2325, 3100, and 2325 possible combinations of 155 studies for the 5-, 4-, 3-, and 2-rabbit subsets, respectively. We classify materials using a four-level adjectival rating system based on (among other factors) the Draize score. Comparisons indicated that 5-, 4-, 3-, and 2-rabbit scores were in 98, 96, 94, and 91% agreement, respectively, with the classification assigned on the basis of the 6-rabbit score. The correlation coefficients for randomly selected subsets of 5-, 4-, 3-, and 2-rabbit scores versus the Draize score for six rabbits were 0.998, 0.996, 0.992, and 0.984, respectively. This study confirms the findings of an earlier report by De Sousa et al. (1984), and indicates that a high level of accuracy can be obtained with reduced numbers of rabbits per test.

Animals↗
PubMed1988

A computerized classification technique for screening for the presence of breath biomarkers in lung cancer.

A simple computer-based screening technique has been developed for classifying human expired air components into 16 chemical classes, based on empirical formulas. The sort procedure was developed to simplify the screening of the composition of expired air samples by sorting all components into chemical classes and classifying components at the greater than 75% and greater than 90% occurrence levels. Both occurrence-rate components are then evaluated as diagnostic markers in a discriminant function model for their ability to detect lung cancer. Of the 386 components detected in the gas chromatography/mass spectrometry (GC/MS) data files, 45 components were present at the greater than 75% occurrence level and 28 components at the greater than 90% occurrence level. Thus, this preliminary sort routine, performed by using a simple macro program installed into a standard personal-computer spread-sheet, greatly reduces the amount of data required for statistical treatment. Such a sort routine can also be applied as easily to other complex GC/MS data files for the purpose of data reduction.

Biomarkers, Tumor↗
PubMed1987

A double-blind, placebo-controlled trial of lithium carbonate therapy for alcoholism.

The efficacy of lithium carbonate as a treatment for alcoholism was examined in a double-blind, placebo-controlled study of 104 men and women meeting DSM-III criteria for alcohol dependence. Subjects entered the study during inpatient treatment and were subsequently followed up for 12 months. Survival analysis disclosed essentially three categories of treatment response: one for noncompliant subjects (0% to 7% abstinent), one for compliant subjects not attaining therapeutic serum lithium levels (31% to 44% abstinent), and one for compliant subjects with therapeutic serum levels (67% abstinent). Two findings led us to believe that therapeutic serum levels of lithium were associated with better outcome over and above a behavioral compliance effect. First, in a dose-response analysis, serum lithium levels and abstinence rates were not linearly associated. Second, all subjects who started lithium carbonate therapy as inpatients were significantly less likely to relapse to drinking during the first month than were placebo-compliant subjects. There was no evidence that depressed alcoholics showed a better treatment response than nondepressed alcoholics or that lithium had any significant impact on the mood or social adjustment of alcoholics. Although the sample size and the difficulties of ascertaining placebo compliance caution against drawing firm conclusions, the data add further support to the hypothesis that lithium has an effect on drinking behavior not related to the treatment of affective symptoms.

Adult↗
PubMed1987

Methodology in psychiatric research. Report on the 1986 MacArthur Foundation Network I Methodology Institute.

This report discusses many of the issues raised during a two-day institute that focused on methodological problems encountered in psychiatric research. The topics range from the problems with psychiatric diagnosis and measurement to sampling issues and biases to specific statistical concerns. Attention is given to the need for improved communication and collaboration between psychiatric researchers and biostatisticians.

Biometry↗
PubMed1987

Regression toward the mean: more on the price of beer and the salaries of priests.

Investigators must take great care in studying the temporal association between biological and clinical data. By selecting patients on the basis of deviant levels of a biological parameter, it often is impossible to separate the effect of regression toward the mean from a temporal association of clinical interest. Experimental strategies that focus exclusively on subjects with extreme values are particularly prone to misinterpreting the effects of regression toward the mean as a temporal change in the variable of interest. We cite specific examples of two previous studies of the relationship between the dexamethasone suppression test (DST) and clinical response in depression. Contrary to the conclusions of the investigators, normalization of the DST had no relation to clinical response in the first 5 weeks of treatment. The decrease of post-dexamethasone cortisol levels occurred regardless of clinical response, most likely due to the effect of regression toward the mean.

Antidepressive Agents↗