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Testing zero variance components is one of the most challenging problems in the context of linear mixed-effects (LME) models. The usual asymptotic chi-square distribution of the likelihood ratio and score statistics under this null hypothesis is incorrect because the null is on the boundary of the parameter space. During the last two decades many tests have been proposed to overcome this difficulty, but these tests cannot be easily applied for testing multiple variance components, especially for testing a subset of them. We instead introduce a simple test statistic based on the variance least square estimator of variance components. With this comes a permutation procedure to approximate its finite sample distribution. The proposed test covers testing multiple variance components and any subset of them in LME models. Interestingly, our method does not depend on the distribution of the random effects and errors except for their mean and variance. We show, via simulations, that the proposed test has good operating characteristics with respect to Type I error and power. We conclude with an application of our process using real data from a study of the association of hyperglycemia and relative hyperinsulinemia. © 2012 The Author.

1 april 2010, Contains fulltext : 89166.pdf (publisher's version ) (Closed access), AIMS: To evaluate the effectiveness of a two-arm quality improvement program (QIP) to support general practice with limited tradition in chronic care on type 2 diabetes patient outcomes. METHODS: During 18 months, we performed a cluster randomized trial with randomization of General Practices. The usual QIP (UQIP: 53 GPs, 918 patients) merged standard interventions including evidence-based treatment protocol, annual benchmarking, postgraduate education, case-coaching for GPs and patient education. The advanced QIP (AQIP: 67 GPs, 1577 patients) introduced additional interventions focussing on intensified follow-up, shared care and patient behavioural changes. Main outcomes were HbA1c, systolic blood pressure (SBP), and low density lipoprotein cholesterol (LDL-C), analyzed by generalized estimating equations and linear mixed models. RESULTS: In UQIP, endpoints improved significantly after intervention: HbA1c -0.4%, 95% CI [-0.4; -0. 3]; SBP -3mmHg, 95% CI [-4; -1]; LDL-C -13mg/dl, 95% CI [-15; -11]. In AQIP, there were no significant additional improvements in outcomes: HbA1c -0.4%, 95% CI [-0.4; -0.3]; SBP -4mmHg, 95% CI [-5; -2]; LDL-C -14mg/dl, 95% CI [-15; -11]. CONCLUSIONS: A multifaceted program merging standard interventions in support of general practice induced significant improvements in the quality of diabetes care. Intensified follow-up in AQIP with focus on shared care and patient behaviour changes did not yield additional benefit.

1 juli 2010, Contains fulltext : 89159.pdf (publisher's version ) (Closed access), BACKGROUND: Because many patients in usual care reach the diabetes treatment goals, it may be more efficacious to focus quality improvement efforts on those general practice populations requiring additional support. We therefore developed a tool based on a composite end point considering blood pressure, lipids, and glycaemia. METHODS: We created an aggregated z(A)-score, calculated as the average of 3 z-scores testing whether the mean practice values of hemoglobin A1c, low density lipoprotein cholesterol, and systolic blood pressure are significantly higher than the corresponding ADA-target (respectively 7%, 100 mg/dL, and 130 mm Hg). This score was used with 100 general practitioners who participated in a Quality Improvement Program. We defined the cut-off value (COV) to determine "Practices Requiring Support" (z(A)

Background. In the working population, back disorders are an important reason for sick leave and permanent work inability. In the context of fitting the job to the worker, one of the primary tasks of the occupational health physician is to evaluate the balance between work-related and individual variables. Since this evaluation of work capacity often consists of a physical examination of the back, the objective of this study was to investigate whether a physical examination of the low back, which is routinely performed in occupational medicine, predicts the development of low back pain (LBP). Methods. This study is part of the Belgian Low Back Cohort (BelCoBack) Study, a prospective study to identify risk factors for the development of low back disorders in occupational settings. The study population for this paper were 692 young healthcare or distribution workers (mean age of 26 years) with no or limited back antecedents in the year before inclusion. At baseline, these workers underwent a standardised physical examination of the low back. One year later, they completed a questionnaire on the occurrence of LBP and some of its characteristics. To study the respective role of predictors at baseline on the occurrence of LBP, we opted for Cox regression with a constant risk period. Analyses were performed separately for workers without any back antecedents in the year before inclusion ('asymptomatic' workers) and for workers with limited back antecedents in the year before inclusion ('mildly symptomatic' workers). Results. In the group of 'asymptomatic' workers, obese workers showed a more than twofold-increased risk on the development of LBP as compared to non-obese colleagues (RR 2.57, 95%CI: 1.09 - 6.09). In the group of 'mildly symptomatic' workers, the self-reports of pain before the examination turned out to be most predictive (RR 3.89, 95%CI: 1.20 - 12.64). Conclusion. This study showed that, in a population of young workers wh no or limited antecedents of LBP at

Contains fulltext : 80136.pdf (publisher's version ) (Open Access), BACKGROUND: Type 2 diabetes mellitus is a complex, progressive disease which requires a variety of quality improvement strategies. Limited information is available on the feasibility and effectiveness of interdisciplinary diabetes care teams (IDCT) operating on the interface between primary and specialty care. A first study hypothesis was that the implementation of an IDCT is feasible in a health care setting with limited tradition in shared care. A second hypothesis was that patients who make use of an IDCT would have significantly better outcomes compared to non-users of the IDCT after an 18-month intervention period. A third hypothesis was that patients who used the IDCT in an Advanced quality Improvement Program (AQIP) would have significantly better outcomes compared to users of a Usual Quality Improvement Program (UQIP). METHODS: This investigation comprised a two-arm cluster randomized trial conducted in a primary care setting in Belgium. Primary care physicians (PCPs, n = 120) and their patients with type 2 diabetes mellitus (n = 2495) were included and subjects were randomly assigned to the intervention arms. The IDCT acted as a cornerstone to both the intervention arms, but the number, type and intensity of IDCT related interventions varied depending upon the intervention arm. RESULTS: Final registration included 67 PCPs and 1577 patients in the AQIP and 53 PCPs and 918 patients in the UQIP. 84% of the PCPs made use of the IDCT. The expected participation rate in patients (30%) was not attained, with 12,5% of the patients using the IDCT. When comparing users and non-users of the IDCT (irrespective of the intervention arm) and after 18 months of intervention the use of the IDCT was significantly associated with improvements in HbA1c, LDL-cholesterol, an increase in statins and anti-platelet therapy as well as the number of targets that were reached. When comparing users of the IDCT in the two intervention arms no significant differences were noted, except f

Background: In the working population, back disorders are an important reason for sick leave and permanent work inability. In the context of fitting the job to the worker, one of the primary tasks of the occupational health physician is to evaluate the balance between work-related and individual variables. Since this evaluation of work capacity often consists of a physical examination of the back, the objective of this study was to investigate whether a physical examination of the low back, which is routinely performed in occupational medicine, predicts the development of low back pain (LBP). Methods: This study is part of the Belgian Low Back Cohort (BelCoBack) Study, a prospective study to identify risk factors for the development of low back disorders in occupational settings. The study population for this paper were 692 young healthcare or distribution workers ( mean age of 26 years) with no or limited back antecedents in the year before inclusion. At baseline, these workers underwent a standardised physical examination of the low back. One year later, they completed a questionnaire on the occurrence of LBP and some of its characteristics. To study the respective role of predictors at baseline on the occurrence of LBP, we opted for Cox regression with a constant risk period. Analyses were performed separately for workers without any back antecedents in the year before inclusion ('asymptomatic' workers) and for workers with limited back antecedents in the year before inclusion (' mildly symptomatic' workers). Results: In the group of ' asymptomatic' workers, obese workers showed a more than twofold-increased risk on the development of LBP as compared to non-obese colleagues (RR 2.57, 95% CI: 1.09-6.09). In the group of ' mildly symptomatic' workers, the self-reports of pain before the examination turned out to be most predictive ( RR 3.89, 95% CI: 1.20-12.64). Conclusion: This study showed that, in a population of young workers wh no or limited antecedents of LBP

Contains fulltext : 70617.pdf (publisher's version ) (Open Access), BACKGROUND: Most quality improvement programs in diabetes care incorporate aspects of clinician education, performance feedback, patient education, care management, and diabetes care teams to support primary care physicians. Few studies have applied all of these dimensions to address clinical inertia. AIM: To evaluate interventions to improve adherence to evidence-based guidelines for diabetes and reduce clinical inertia in primary care physicians. DESIGN: Two-arm cluster randomized controlled trial. PARTICIPANTS: Primary care physicians in Belgium. INTERVENTIONS: Primary care physicians will be randomly allocated to 'Usual' (UQIP) or 'Advanced' (AQIP) Quality Improvement Programs. Physicians in the UQIP will receive interventions addressing the main physician, patient, and office system factors that contribute to clinical inertia. Physicians in the AQIP will receive additional interventions that focus on sustainable behavior changes in patients and providers. OUTCOMES: Primary endpoints are the proportions of patients within targets for three clinical outcomes: 1) glycosylated hemoglobin < 7%; 2) systolic blood pressure differences

Udgivelsesdato: 2007