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Biomedical subjects

G Marshall

Publications and source records attributed to G Marshall.

At least 55 records · Page 3Linked to original sources
PubMed1998

Longer-term effects of corrective input: an experimental approach.

There is growing evidence that corrective input for grammatical errors is widely available to children (Farrar, 1992; Morgan, Bonamo & Travis, 1995). However, controversy still exists concerning the extent to which children can identify and exploit available negative input. In particular, very little is yet known about the longer-term effects of negative input. Performing a time series analysis on observational data, Morgan et al. (1995) conclude that corrective recasts are not related to future improvements in grammaticality. It is argued here, though, that the data sets analysed in this study are inherently ill-suited to the demands of time series analyses. The present study adopts an experimental approach in order to compare the effects of negative evidence versus positive input on the acquisition of irregular past tense verb forms. Twenty-six children (mean age 3;10) participated in a within-subjects design over a period of five weeks. It was found that improvements in the grammaticality of child speech were considerably greater in cases where negative evidence had been provided. Moreover, children's intuitions concerning the status of irregular and overregularized forms more closely approximated adult intuitions when corrective input was available.

Child Language↗
PubMed1998

Time series monitors of outcomes. A new dimension for measuring quality of care.

OBJECTIVES: Despite the popularity of risk-adjusted outcomes as quality of health care indicators, their instability with time and their inability to provide reliable comparisons of small volume providers have raised questions about the feasibility and credibility of using these measures. In this article the authors describe a new analytic strategy to address these problems by examining risk-adjusted mortality with time, "Time Series Monitors of Outcome" (TSMO), and its application to cardiac surgery performed throughout the Department of Veterans Affairs between April 1987 and September 1992. METHODS: Expected operative mortality for 24,029 patients undergoing coronary artery bypass surgery at all 43 centers performing this procedure was estimated using a logistic regression model to adjust for patient-specific risk factors. The ratio of observed-to-expected operative mortality was calculated for each hospital for each of the 11 6-month periods. Poisson regression models were used to identify high and low outlier hospitals based on significant deviation from the 5.5 year overall mean and/or the individual hospital's trend of observed-to-expected ratios with time. RESULTS: This method identified four high and one low outlier hospitals based on significant deviations from the overall mean and three upward and seven downward trending outlier hospitals based on significant deviations in trend with time. A significant downward trend in observed-to-expected ratios of 4% per year also was observed for all coronary artery bypass graft procedures performed throughout the Department of Veterans Affairs during the last 5.5 year period. CONCLUSIONS: Time Series Monitors of Outcome should help reduce misclassification of outliers due to random variation in outcomes as well as provide more reliable comparative information from which to evaluate provider performance.

Coronary Artery Bypass↗
PubMed1997

Neuronally restricted RNA splicing regulates the expression of a novel GABAA receptor subunit conferring atypical functional properties [corrected; erratum to be published].

We report the isolation and characterization of a cDNA encoding a novel member of the GABA receptor gene family, epsilon. This polypeptide is 506 amino acids in length and exhibits its greatest amino acid sequence identity with the GABAA receptor gamma3 subunit (47%), although this degree of homology is not sufficient for it to be classified as a fourth gamma subunit. The epsilon subunit coassembles with GABAA receptor alpha and beta subunits in Xenopus laevis oocytes and transfected mammalian cells to form functional GABA-gated channels. alpha1beta1epsilon GABAA receptors, like alpha1beta1gamma2s receptors, are modulated by pentobarbital and the steroid 5alpha-pregnan-3alpha-ol-20-one but, unlike alpha1beta1gamma2s receptors, are insensitive to flunitrazepam. Additionally, alpha1beta1epsilon receptors exhibit rapid desensitization kinetics, as compared with alpha1beta1 or alpha1beta1gamma2s. Northern analysis demonstrates widespread expression of a large epsilon subunit transcript in a variety of non-neuronal tissues and expression of a smaller transcript in brain and spinal cord. Sequence analysis demonstrated that the large transcript contained an unspliced intron, whereas the small transcript represents the mature mRNA, suggesting regulation of expression of the epsilon subunit via neuronally restricted RNA splicing. In situ hybridization and immunocytochemistry reveal a pattern of expression in the brain restricted primarily to the hypothalamus, suggesting a role in neuroendocrine regulation, and also to subfields of the hippocampus, suggesting a role in the modulation of long term potentiation and memory.

Amino Acid Sequence↗
PubMed1997

Comparison of dentinal crack incidence and of post removal time resulting from post removal by ultrasonic or mechanical force.

The purpose of this study was to compare the frequency of canal and intradentin cracks after intraradicular post removal using ultrasonic instrumentation or the Gonan post removal system. Sixty cadaver teeth were divided into 4 groups of 15 teeth each: group 1, ultrasonic removal; group 2, Gonan post removal system; group 3, cemented posts not removed; and group 4, no posts. Groups 1 and 2 were contralateral matched pairs. Para Posts were placed in groups 1, 2, and 3 to 7 mm apical to the cementoenamel junction and luted with ZnPO4 cement. The time required for post removal in groups 1 and 2 was recorded. The teeth were extracted, sectioned, and examined. Canal and intradentin cracks were mapped, and their frequency was recorded at each level. There were statistically more cracks present in the ultrasonic group than the no post group. There were no other differences that reached statistical significance. It took significantly longer for post removal using the ultrasonic tip versus the Gonan system.

Cadaver↗
PubMed1997

24-h ambulatory blood pressure monitoring in healthy young adult Anglo, Hispanic, and African-American subjects.

The purpose of this study was to compare office and 24-h ambulatory blood pressure (ABP) values for adolescent and young adult males and females of Anglo, Hispanic, and African-American descent. One hundred and eighteen healthy subjects (62 females, 56 males) participated, with an ethnic distribution of 50 Anglo, 32 Hispanic, and 36 African-American subjects. All subjects came to the clinic for height, weight, sitting blood pressure (BP), and to begin 24-h ABP monitoring using the SpaceLabs model 90207 automatic noninvasive monitor. The monitor recorded readings every 0.5 h from 06:00 to 22:00 and every hour at night from 22:00 to 06:00. Office systolic and diastolic BP values were higher for all males compared to all females. Mean 24-h, nighttime, and daytime systolic ABP values were also significantly higher for males compared to females. The 24-h mean and daytime systolic ABP values were significantly different by ethnic groups. The African-American subjects always had the highest readings. Mean 24-h diastolic ABP was also significantly different by ethnic groups, with the African-American subjects being higher than the Anglos or the Hispanics. Diastolic ABP (24-h mean, daytime, and nighttime) values (for all subjects combined) increased gradually and varied significantly with age. This study provides preliminary normative data about ABP in an understudied population (ie, teenagers and young adults of different ethnic backgrounds). It also shows that higher blood pressures are present among males and among subjects of African-American descent in the teenage and young adult population.

Adult↗
PubMed1997

Cholesterol crystals in hydroceles: sonographic detection and possible significance.

OBJECTIVE: The aim of this study of seven patients who had elective surgical repairs of a hydrocele was to try to differentiate by microscopy and chemical analysis hyperechoic hydrocele fluid from the more typical anechoic hydrocele fluid. CONCLUSION: Hyperechoic hydrocele fluid is related to the presence of cholesterol crystals. Cholesterol crystals were noted on microscopic examination in all three patients with hyperechoic hydrocele fluid. No cholesterol crystals were evident in the four patients with typical anechoic hydrocele fluid.

Adult↗
PubMed1996

No continuous relationship between Veterans Affairs hospital coronary artery bypass grafting surgical volume and operative mortality.

BACKGROUND: The purpose of this study was to determine whether risk-adjusted coronary artery bypass grafting mortality rates are significantly related to coronary artery bypass grafting surgical procedure volume within the Department of Veterans Affairs hospital system. METHODS: From April 1987 to September 1992, expected mortality rates were calculated for 23,986 coronary artery bypass grafting procedures performed at 44 different Veterans Affairs hospitals. RESULTS: This study found a statistically significant relationship between annual hospital coronary artery bypass grafting volume and observed mortality rates (p < 0.02). However, no statistically significant relationship between coronary artery bypass grafting volume and risk-adjusted operative mortality was found (p = 0.10). Using analysis of variance on hospital-level data, hospitals with 100 or less cases per year have higher observed to expected mortality ratios than hospitals performing more than 100 cases per year (p = 0.03). Using Poisson regression models, however, a volume threshold could not be found. CONCLUSIONS: These findings are consistent with the current Veterans Affairs policy requirements to periodically review quality at low-volume hospitals.

Analysis of Variance↗
PubMed1995

Multi-state models and diabetic retinopathy.

This paper discusses the application of a multi-state model to diabetic retinopathy under the assumption that a continuous time Markov process determines the transition times between disease stages. The multi-state model consists of three transient states that represent the early stages of retinopathy, and one final absorbing state that represent the irreversible stage of retinopathy. By using a model with covariables, we explore the effects of factors that influence the onset, progression, and regression of diabetic retinopathy among subjects with insulin-dependent diabetes mellitus. We can also introduce time-dependent covariables in the model by assuming that the covariables remain constant between two observations. We can also obtain survival-type curves from each stage of the disease and for any combination of patient risk factors.

Adolescent↗
PubMed1995

Human immunodeficiency virus seroprevalence in community-based primary care practices, 1990-1992. A report from the Ambulatory Sentinel Practice Network.

OBJECTIVE: To estimate the seroprevalence of human immunodeficiency virus type 1 (HIV-1) infection in primary care practices. METHODS: Fifty-four practices in the United States participated in an anonymous, unlinked HIV seroprevalence study between January 1990 and December 1992. Residual blood samples drawn for routine clinical tests from patients 15 to 49 years of age were centrally tested for the HIV-1 antibody for 1 month of each quarter. Information about patient demographics, clinician-recognized risk factors, the known HIV status of the patient, and whether the blood was drawn for HIV testing was recorded with each specimen. RESULTS: Of 21,998 specimens collected, 99 (0.45%) were seropositive. Of these 99 seropositive persons, 31.3% (a seroprevalence of 0.15%) were not suspected by their clinicians of being infected with HIV. Seroprevalences in men (0.96%) exceeded those in women (0.22%), and rates in rural practices (0.18%) were lower than in urban practices (0.71%). Among patients with unsuspected HIV infection, however, the gender differences, especially in rural areas, were less pronounced. Risk factors for HIV infection were infrequently noted. There was an increase in the overall seroprevalence during the 1990 to 1992 study period (0.36% to 0.53%); however, this trend was not statistically significant. CONCLUSIONS: Within a 3-year period, clinicians in at least two of five primary care practices can expect to encounter patients infected with HIV, regardless of practice location. Also, nearly one third of the patients with HIV infection will not be suspected of having this condition by their clinician.

Adolescent↗
PubMed1995

ORDMKV: a computer program fitting proportional odds model for multi-state Markov process.

ORDMKV is a computer program designed to fit a multi-state discrete-time Markov model for k-stages disease processes having an ordinal structure. The model consists of k transient states representing the increasing severity of the disease process, and the final state can be optionally chosen to be an absorbing state in cases such as death. The ordinal structure of the stages of the disease is modelled by using ordinal response models. Each row of the one-step transition probability matrix is modelled using a proportional odds model based on the cumulative transition probabilities. By using these ordinal response models, the number of parameters used to model the disease process can be reduced significantly not only with respect to a general discrete-time model, but also compared with a parsimonuos continuous-time model. A restricted model can be fitted by assuming that the effect of the covariables in the cumulative probability has common regression coefficients in all stages of the disease process. This assumption, if it holds, reduces the number of regression coefficients associated with each covariate to only one. The regression coefficients of this model are estimated via the method of maximum likelihood, using a quasi-Newton optimization algorithm. When the last state is considered as an absorbing state, it is possible to compute survival curves from the transient states of the process. The program was written in standard FORTRAN 77 and is illustrated using a four-state model to determine factors influencing diabetic retinopathy in young subjects with insulin-dependent diabetes mellitus.

Diabetes Mellitus, Type 1↗
PubMed1995

MARKOV: a computer program for multi-state Markov models with covariables.

This paper discusses a computer program, called MARKOV, designed to fit a multi-state Markov model with covariables, with a particular emphasis on the analysis of survival data. The Markov model consists of k-1 transient disease states and one absorbing state. The exact transition times are not observed, except in situations such as death. Baseline transition intensities and regression coefficients are estimated via the method of maximum likelihood using a quasi-Newton optimization algorithm. The program's output includes the parameter estimates, the standard error of the estimates, the matrix of the correlation of the estimates and minus two times the log-likelihood function, evaluated at the initial values and at the maximum likelihood estimates. Optionally, survival curves can be generated from each transient state, for one or more combination of covariable values and simple tests about the parameters. The program is illustrated by using a four-state model to determine factors influencing diabetic retinopathy in young subjects with insulin-dependent diabetes mellitus.

Algorithms↗
PubMed1995

The Processes, Structures, and Outcomes of Care in Cardiac Surgery study protocol.

Recently, a growing interest has arisen in defining and measuring health care outcomes. Although outcome measures may be used as potential quality-of-care screens, outcomes cannot indicate directly how care might be improved. Thus, the Processes, Structures, and Outcomes of Care in Cardiac Surgery (PSOCS) study was designed to investigate the linkages between the processes and structures of care with risk-adjusted outcomes for cardiac surgery care. Data are being collected on a comprehensive array of risk factors, processes, structures, and outcomes of care at 14 Veterans Affairs Medical Centers for this prospective, observational study. Approximately 6,000 cardiac surgery patients will be enrolled in this study over a 4.5-year period. Patient selection is based on a 6 workday rotating sampling frame with an oversampling of emergent patients. During the study, a register of all patients undergoing cardiac surgery at these centers is being maintained to assess the overall context of patient recruitment. The study will continue to enroll patients through December 1996. Major study end points extend beyond traditional measures of 30-day mortality and morbidity to encompass more innovative intermediate outcome measures, including changes in physical functional status and health-related quality of life.

Aged↗
PubMed1995

Relationships between patient-related risk factors, processes, structures, and outcomes of cardiac surgical care. Conceptual models.

The processes, Structures, and Outcomes of Care in Cardiac Surgery (PSOCS) study involves data collection on a comprehensive array of patient risk factors, processes, structures, and short-term outcomes of care at 14 participating Veterans Administration medical centers. This article summarizes the PSOCS conceptual models that serve as the theoretical framework for analyzing the hypothesized risk-process-structure-outcome relationships being investigated. The PSOCS data set includes more than 1,100 variables related to each patient and more than 300 variables related to provider-specific and facility-specific characteristics. This massive data set presents a formidable analytic challenge. The conceptual modeling process involved four-steps: 1) establishing a vision of the general conceptual model defining the overall risk-process-structure-outcome relationships, 2) developing specific hypotheses or subhypotheses, 3) visualizing a hierarchical set of dimensions and subdimensions, and 4) uniquely assigning each variable collected in the study to a dimension or subdimension for purposes of testing the study's primary hypotheses. A multidisciplinary team participated in this modeling process. The goal of the conceptual modeling process is to identify clearly the actions (ie, the changes in either processes or structures that are linked to risk-adjusted patient outcomes) that can be taken by clinicians, management, and policymakers to improve the quality of cardiac surgical care.

Cardiac Surgical Procedures↗
PubMed1995

Statistical methods and strategies for working with large data bases.

This article describes the statistical methods and strategies to be used in establishing the linkages between processes and structures of care with risk-adjusted outcomes in a large multicenter Veterans Affairs cooperative study in health services of patients undergoing cardiac surgery. The statistical analyses consist of test involving nine specific hypotheses related to the effect of processes and structures of care on risk-adjusted outcomes. From the statistical point of view, the major obstacles of this study are the need for data reduction and imputation of missing data. The former obstacle is addressed through the use of data-reduction techniques, such as principal components and cluster of variables. The latter is addressed through the use of classic and new techniques for imputation of missing data, such as MISSGEN, principal components for qualitative data, and the expectation and maximization algorithm. Data reduction and imputation of missing data are done with clinically derived variable groups called "dimensions" or "subdimensions." The effect of processes and structures of care is assessed by a two-step process. First, outcomes are modeled using only patient risk factors. The selection of risk factors in the modeling process is discussed in detail. Second, these risk-adjusted outcomes are modeled using one of the nine process or structure subhypotheses. The relationship of the processes and structures of care dimensions and/or subdimensions that are linked to risk-adjusted outcomes are identified.

Cardiac Surgical Procedures↗
PubMed1995

An analysis of interobserver reliability and representativeness of data from the Veterans Affairs Cooperative Study on Processes, Structures, and Outcomes in Cardiac Surgery.

The authors made some preliminary judgments regarding the reliability and representativeness of the data in the early stages of the Veterans Affairs Cooperative Study entitled Processes, Structures, and Outcomes of Care in Cardiac Surgery (PSOCS). Preliminary PSOCS interobserver reliability and potential patient and site selection bias reported were based on comparisons with identical risk, procedure, and outcome data items collected independently in the Continuous Improvement in Cardiac Surgery Study. PSOCS interobserver reliability for this limited set of variables was good to excellent. At the six pilot centers, there were few important differences between patients entered into PSOCS and those not entered. The 14 Veterans Affairs medical centers that will participate in the full-scale PSOCS study and the 29 nonparticipating centers exhibited similar patient populations. will be valuable.

Cardiac Surgical Procedures↗
PubMed1995

Final adult height and its relationship to blood glucose control and microvascular complications in IDDM.

The effect of longitudinal blood glucose control on final adult height was evaluated in 181 subjects (94 women and 87 men) with IDDM. Diabetes onset was at a median age of 6.9 years with an interquartile range of 4.7 years. Longitudinal glycated haemoglobin values were determined over a mean period of 6.6 +/- 2.6 years during their growth phase. Serial eye and joint examinations and urinary albumin excretion rates were performed with final assessment being carried out at a mean age of 21.1 +/- 3.0 years. The mean adult height standard deviation score of the whole group was -0.22 +/- 1.15 and was reduced compared to the mean height of the general population and to the mean height of the subjects' parents and siblings. There was an inverse correlation with mean longitudinal glycated haemoglobin and final adult height (p < 0.01). There was also an inverse relationship between adult height and the severity of eye, kidney, and joint complications, but when controlled by glycated haemoglobin, this relationship only remained significant for eye complications. Final adult height is reduced in subjects with early onset IDDM who remain in poor blood glucose control during their growth period.

Adult↗