Biomedical subjects

Rumana Z Omar

Publications and source records attributed to Rumana Z Omar.

12 recordsLinked to original sources

PubMed2006

Constructing intervals for the intracluster correlation coefficient using Bayesian modelling, and application in cluster randomized trials.

Studies in health research are commonly carried out in clustered settings, where the individual response data are correlated within clusters. Estimation and modelling of the extent of between-cluster variation contributes to understanding of the current study and to design of future studies. It is common to express between-cluster variation as an intracluster correlation coefficient (ICC), since this measure is directly comparable across outcomes. ICCs are generally reported unaccompanied by confidence intervals. In this paper, we describe a Bayesian modelling approach to interval estimation of the ICC. The flexibility of this framework allows useful extensions which are not easily available in existing methods, for example assumptions other than Normality for continuous outcome data, adjustment for individual-level covariates and simultaneous interval estimation of several ICCs. There is also the opportunity to incorporate prior beliefs on likely values of the ICC. The methods are exemplified using data from a cluster randomized trial.

Bayes Theorem↗

PubMed2006

Quality research in healthcare: are researchers getting enough statistical support?

BACKGROUND: Reviews of peer-reviewed health studies have highlighted problems with their methodological quality. As published health studies form the basis of many clinical decisions including evaluation and provisions of health services, this has scientific and ethical implications. The lack of involvement of methodologists (defined as statisticians or quantitative epidemiologists) has been suggested as one key reason for this problem and this has been linked to the lack of access to methodologists. This issue was highlighted several years ago and it was suggested that more investments were needed from health care organisations and Universities to alleviate this problem. METHODS: To assess the current level of methodological support available for health researchers in England, we surveyed the 25 National Health Services Trusts in England, that are the major recipients of the Department of Health's research and development (R&D) support funding. RESULTS AND DISCUSSION: The survey shows that the earmarking of resources to provide appropriate methodological support to health researchers in these organisations is not widespread. Neither the level of R&D support funding received nor the volume of research undertaken by these organisations showed any association with the amount they spent in providing a central resource for methodological support for their researchers. CONCLUSION: The promotion and delivery of high quality health research requires that organisations hosting health research and their academic partners put in place funding and systems to provide appropriate methodological support to ensure valid research findings. If resources are limited, health researchers may have to rely on short courses and/or a limited number of advisory sessions which may not always produce satisfactory results.

Biometry↗

PubMed2006

Modelling multivariate outcomes in hierarchical data, with application to cluster randomised trials.

In the cluster randomised study design, the data collected have a hierarchical structure and often include multivariate outcomes. We present a flexible modelling strategy that permits several normally distributed outcomes to be analysed simultaneously, in which intervention effects as well as individual-level and cluster-level between-outcome correlations are estimated. This is implemented in a Bayesian framework which has several advantages over a classical approach, for example in providing credible intervals for functions of model parameters and in allowing informative priors for the intracluster correlation coefficients. In order to declare such informative prior distributions, and fit models in which the between-outcome covariance matrices are constrained, priors on parameters within the covariance matrices are required. Careful specification is necessary however, in order to maintain non-negative definiteness and symmetry between the different outcomes. We propose a novel solution in the case of three multivariate outcomes, and present a modified existing approach and novel alternative for four or more outcomes. The methods are applied to an example of a cluster randomised trial in the prevention of coronary heart disease. The modelling strategy presented would also be useful in other situations involving hierarchical multivariate outcomes.

Artificial Intelligence↗

PubMed2006

Meta-analysis of studies of alcohol and breast cancer with consideration of the methodological issues.

OBJECTIVE: To give an up-to-date assessment of the association of alcohol with female breast cancer, addressing methodological issues and shortfalls in previous overviews. METHODS: Meta-analysis of studies (any language) providing original data on incidence of first primary breast cancer and alcohol. Two reviewers independently extracted data. Study quality assessed by objective criteria including degree of control for confounding; funnel plots examined for publication bias; meta-regression techniques to explore heterogeneity. Risks associated with drinking versus not drinking and dose-response not constrained through the origin estimated using random effects methods. RESULTS: Ninety-eight unique studies were included, involving 75,728 and 60,653 cases in drinker versus non-drinker and dose-response analyses, respectively. Findings were robust to study design and analytic approaches in the meta-analyses. For studies judged high quality, controlled for appropriate confounders, excess risk associated with alcohol drinking was 22% (95% CI: 9-37%); each additional 10 g ethanol/day was associated with risk higher by 10% (95% CI: 5-15%). There was no evidence of publication bias. Risk did not differ significantly by beverage type or menopausal status. Estimated population attributable risks were 1.6 and 6.0% in USA and UK, respectively. CONCLUSIONS: Taking account of shortcomings in the study base and methodological concerns, we confirm the alcohol-breast cancer association. We compared our results to those of an individual patient data analysis, with similar findings. We conclude that the association between alcohol and breast cancer may be causal.

Alcohol Drinking↗

PubMed2006

Association of age, sex and deprivation with quality indicators for diabetes: population-based cross sectional survey in primary care.

OBJECTIVES: To determine the quality of diabetes management in primary care after the publication of the National Service Framework and examine the impact of age, gender and deprivation on the achievement of established quality indicators. DESIGN: Population-based cross sectional survey using electronic general practice records carried out between June-October 2003. SETTING: Thirty-four practices in Wandsworth, South-West London, UK. PARTICIPANTS: 6035 adult patients (> or =18 years) with diabetes from a total registered population of 201,572 patients. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Success rates for the diabetes quality indicators within the General Medical Services contract for general practitioners. RESULTS: We identified large variations in diabetes management between general practitioner practices with poorer recording of quality care in younger patients (18-44 years). In addition, younger patients had a worse cholesterol and glycaemia profile, although hypertension was more common in older patients. Gender and deprivation did not appear to be important determinants of the quality of care received. CONCLUSIONS: There are large variations in diabetes management between general practitioner practices, with care seemingly worse for younger adults. Longitudinal studies are required to determine whether current UK quality improvement initiatives have been successful in attenuating existing variations in care and treatment outcomes.

Adolescent↗

PubMed2005

Generic, simple risk stratification model for heart valve surgery.

BACKGROUND: Heart valve surgery has an associated in-hospital mortality rate of 4% to 8%. This study aims to develop a simple risk model to predict the risk of in-hospital mortality for patients undergoing heart valve surgery to provide information to patients and clinicians and to facilitate institutional comparisons. METHODS AND RESULTS: Data on 32,839 patients were obtained from the Society of Cardiothoracic Surgeons of Great Britain and Ireland on patients who underwent heart valve surgery between April 1995 and March 2003. Data from the first 5 years (n=16,679) were used to develop the model; its performance was evaluated on the remaining data (n=16,160). The risk model presented here is based on the combined data. The overall in-hospital mortality was 6.4%. The risk model included, in order of importance (all P<0.01), operative priority, age, renal failure, operation sequence, ejection fraction, concomitant tricuspid valve surgery, type of valve operation, concomitant CABG surgery, body mass index, preoperative arrhythmias, diabetes, gender, and hypertension. The risk model exhibited good predictive ability (Hosmer-Lemeshow test, P=0.78) and discriminated between high- and low-risk patients reasonably well (receiver-operating characteristics curve area, 0.77). CONCLUSIONS: This is the first risk model that predicts in-hospital mortality for aortic and/or mitral heart valve patients with or without concomitant CABG. Based on a large national database of heart valve patients, this model has been evaluated successfully on patients who had valve surgery during a subsequent time period. It is simple to use, includes routinely collected variables, and provides a useful tool for patient advice and institutional comparisons.

Cardiac Surgical Procedures↗

PubMed2005

Case-mix and variation in specialist referrals in general practice.

BACKGROUND: The potential of a comprehensive measure of patient morbidity to explain variation in referrals to secondary care has not previously been examined in the UK. AIM: To examine the relative role of age, sex and morbidity as defined by the Johns Hopkins ACG Case-Mix System in explaining variations in specialist referrals in general practice. DESIGN OF STUDY: Retrospective study of a cohort of patients followed for 1 year. SETTING: Two hundred and two general practices, with a total list size of 1,161,892, contributing data to the General Practice Research Database. METHOD: Each patient was assigned an ACG and morbidity group, based on their diagnoses, age and sex. The variability in referrals explained by these factors was examined using multilevel logistic regression models by splitting it into variation between practices and variation between patients within practices. RESULTS: The annual median (range) percentage of patients referred was 14.8% (range = 2.4-24.4%). The percentage of patients referred increased with age and morbidity. Morbidity explained 30.4% of the total variation in referrals (composed of variability between and within practices). Age and sex only explained 5.3% of the total variation. The variation attributable to practices was approximately 5%, thus most of the variation occurred within practices. Morbidity was also identified as a better predictor of referral compared to age and sex. CONCLUSIONS: Morbidity explains almost six times more of the variation in general practice referrals than age and sex, although about two-thirds of the variation remains unexplained. Most of the unexplained variation is due to differences within rather than between practices. The amount of variability in referrals between practices may be less than implied by previous studies based on aggregate information. The implications are that any investigation of specialist referrals from general practice should be interpreted cautiously, even after adjustment for age, sex and morbidity.

Adolescent↗

PubMed2004

Cardiac surgery risk modeling for mortality: a review of current practice and suggestions for improvement.

Risk models play a vital role in monitoring health care performances. Despite extensive research and widespread use of risk models in cardiac surgery, there are methodologic problems. We reviewed the methodology used for risk models for short-term mortality. The findings suggest that many risk models are developed in an ad hoc manner. Important aspects such as selection of risk factors, handling of missing values, and size of the data used for model development are not dealt with adequately. Methodologic details presented in publications are often sparse and unclear. Model development and validation processes are not always linked to the clinical aim of the model, which may affect their clinical validity. We make some suggestions in this review for improvement in methodology and reporting.

Cardiac Surgical Procedures↗

PubMed2004

Adjusting for case mix and social class in examining variation in home visits between practices.

OBJECTIVES: The purpose of this study was to investigate whether adjusting for clinical case mix and social class explains more of the variation in home visits between general practices than adjusting for age and sex alone. METHODS: The setting was 60 general practices in England and Wales taking part in the 1 year Fourth National Morbidity Survey. The participants comprised 349 505 patients who were registered with one of the participating general practices for at least 180 days, and who had at least one consultation during the period. The outcome measure is whether or not a patient received a home visit in that year. A clinical case mix category (morbidity class) based on 1 year's diagnostic information was assigned to each patient using the Johns Hopkins Adjusted Clinical Groups (ACG) Case Mix System. The social class measure was derived from occupation and employment status and is similar to that of the 1991 UK census. Variations in home visits between practices were examined using multilevel logistic regression models. The variability between practices before and after adjusting for clinical case mix and social class was estimated using the intracluster correlation coefficient (ICC). RESULTS: The overall percentage of patients receiving a home visit over the 1 year study period was 17%, and this varied from 7 to 31% across the 60 practices. The percentage of the total variation in home visits attributable to differences between practices was 2.5% [95% confidence interval (CI) 1.4-3.2%] after adjusting for age and sex. This reduced to 1.6% (95% CI 1.1-2.4%) after taking into account morbidity class. The results were similar when social class was included instead of morbidity class. Morbidity and social class together reduced variation in home visits between practices to 1.5% (95% CI 1.1-2.2%). CONCLUSIONS: Age, sex, social class and clinical case mix are strong determinants of home visits in the UK. Adjusting for morbidity and social class results in a small improvement in explaining the variability in home visits between practices compared with adjusting for age and sex alone. There is far more variation between patients within practices; however, it is not straightforward to examine the factors influencing this variation. In addition to morbidity and social class, there could also be other unmeasured factors such as varying patient demand for home visits, disability or differences in GP home visiting practice style that could influence the large within-practice variability observed in this study.

Adolescent↗

PubMed2003

Off-Pump Coronary Artery Bypass (OPCAB) surgery reduces risk-stratified morbidity and mortality: a United Kingdom Multi-Center Comparative Analysis of Early Clinical Outcome.

OBJECTIVE: Off-Pump Coronary Artery Bypass (OPCAB) surgery is gaining more popularity worldwide. The aim of this United Kingdom (UK) multi-center study was to assess the early clinical outcome of the OPCAB technique and perform a risk-stratified comparison with the conventional Coronary Artery Bypass Grafting (CABG) using the Cardio-Pulmonary Bypass (CPB) technique. METHODS: Data were collected on 5,163 CPB patients from the database of the National Heart and Lung institute, Imperial College, University of London, and on 2,223 OPCAB patients from eight UK cardiac surgical centers, which run established OPCAB surgery programs. All patients had undergone primary isolated CABG for multi-vessel disease through a midline sternotomy approach, between January 1997 and April 2001. Postoperative morbidity and mortality were compared between the CPB and OPCAB patients after adjusting for case-mix. The mortality of the OPCAB patients was also compared, using risk stratification, to the mortality figures reported by the Society of Cardiothoracic Surgeons of Great Britain and Ireland (SCTS) based on 28,018 patients in the national database who were operated on between January 1996 and December 1999. RESULTS: Morbidity and mortality were significantly lower in the OPCAB patients compared with the CPB patients and the UK national database of CABG patients, over the same period of time, after adjusting for case-mix. CONCLUSIONS: This study demonstrates that risk stratified morbidity and mortality are significantly lower in OPCAB patients than CPB patients and patients in the UK national database.

Adult↗

PubMed2003

Use of flexibility tests in the manufacturing process of 60 degrees Björk-Shiley convexo-concave valves and the risk of outlet strut fracture.

OBJECTIVES: Outlet strut fracture remains a concern for 30,000 patients living with a Björk-Shiley convexo-concave heart valve (Shiley, Inc, Irvine, Calif, a subsidiary of Pfizer, Inc). Previous studies (Netherlands and United Kingdom) investigating valve manufacturing aspects identified multiple performance of the hook deflection test as a risk factor for 60 degrees valves. The present study validated this finding using new data with a greater number of valves implanted worldwide. Risks of outlet strut fracture associated with other manufacturing aspects were also investigated. METHODS: A matched case-control study design was used including 416 outlet strut fracture cases and 803 controls. RESULTS: Analyses similar to that of the Dutch and United Kingdom studies produced odds ratios of 3.4 (95% confidence interval [CI]: 1.1-10.3) and 2.8 (95% CI: 1.1-7.3), respectively, for multiple hook deflection tests. Load deflection test, which replaced the hook deflection test, showed a statistically significant association with outlet strut fracture: odds ratio of 5.0 (95% CI: 2.1-11.8) and 6.2 (95% CI: 2.2-18.0) for single and multiple load deflection tests, respectively. An analysis where hook deflection tests were separated from load deflection tests showed significantly elevated odds ratios with performance of any type of flexibility test, and the highest odds ratio was observed with a combined performance of load and hook deflection tests. CONCLUSIONS: Multiple hook deflection tests can now be considered for inclusion in the risk model used for guidelines on explant surgery to improve prediction of outlet strut fracture and provide patient reassurance. Load deflection tests and combined performance of hook and load deflection tests were found to be significant risk factors. No outlet strut fractures were reported for valves manufactured after March 1984 when the load deflection test was still in place. Examining manufacturing documents for these valves may identify new risk factors that could be responsible for the outlet strut fractures risk that remains unexplained to date.

Heart Valve Prosthesis↗

PubMed2003

Effectiveness of supervised physical therapy in the early period after arthroscopic partial meniscectomy.

BACKGROUND AND PURPOSE: Controversy exists about the effectiveness of physical therapy after arthroscopic partial meniscectomy. This randomized controlled trial evaluated the effectiveness of supervised physical therapy with a home program versus a home program alone. SUBJECTS: Eighty-four patients (86% males; overall mean age=39 years, SD=9, range=21-58; female mean age=39 years, SD=9, range=24-58; male mean age=40, SD=9, range=21-58) who underwent an uncomplicated arthroscopic partial meniscectomy participated. METHODS: Subjects were randomly assigned to either a group who received 6 weeks of supervised physical therapy with a home program or a group who received only a home program. Blinded test sessions were conducted 5 and 50 days after surgery. Outcome measures were: (1) Hughston Clinic questionnaire, (2) Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) and EuroQol EQ-5D (EQ-5D) questionnaires, (3) number of days to return to work after surgery divided by the Factor Occupational Rating System score, (4) kinematic analysis of knee function during level walking and stair use, and (5) horizontal and vertical hops. RESULTS: No differences between groups were found for any of the outcomes measured. DISCUSSION AND CONCLUSION: The results indicate that the supervised physical therapy used in this study is not beneficial for patients in the early period after uncomplicated arthroscopic partial meniscectomy.

Adult↗