Biomedical subjects

Lydia Guittet

Publications and source records attributed to Lydia Guittet.

4 recordsLinked to original sources

PubMed2006

Planning a cluster randomized trial with unequal cluster sizes: practical issues involving continuous outcomes.

BACKGROUND: Cluster randomization design is increasingly used for the evaluation of health-care, screening or educational interventions. At the planning stage, sample size calculations usually consider an average cluster size without taking into account any potential imbalance in cluster size. However, there may exist high discrepancies in cluster sizes. METHODS: We performed simulations to study the impact of an imbalance in cluster size on power. We determined by simulations to which extent four methods proposed to adapt the sample size calculations to a pre-specified imbalance in cluster size could lead to adequately powered trials. RESULTS: We showed that an imbalance in cluster size can be of high influence on the power in the case of severe imbalance, particularly if the number of clusters is low and/or the intraclass correlation coefficient is high. In the case of a severe imbalance, our simulations confirmed that the minimum variance weights correction of the variation inflaction factor (VIF) used in the sample size calculations has the best properties. CONCLUSION: Publication of cluster sizes is important to assess the real power of the trial which was conducted and to help designing future trials. We derived an adaptation of the VIF from the minimum variance weights correction to be used in case the imbalance can be a priori formulated such as "a proportion (gamma) of clusters actually recruit a proportion (tau) of subjects to be included (gamma < or = tau)".

Analysis of Variance↗

PubMed2006

Methods of blinding in reports of randomized controlled trials assessing pharmacologic treatments: a systematic review.

BACKGROUND: Blinding is a cornerstone of therapeutic evaluation because lack of blinding can bias treatment effect estimates. An inventory of the blinding methods would help trialists conduct high-quality clinical trials and readers appraise the quality of results of published trials. We aimed to systematically classify and describe methods to establish and maintain blinding of patients and health care providers and methods to obtain blinding of outcome assessors in randomized controlled trials of pharmacologic treatments. METHODS AND FINDINGS: We undertook a systematic review of all reports of randomized controlled trials assessing pharmacologic treatments with blinding published in 2004 in high impact-factor journals from Medline and the Cochrane Methodology Register. We used a standardized data collection form to extract data. The blinding methods were classified according to whether they primarily (1) established blinding of patients or health care providers, (2) maintained the blinding of patients or health care providers, and (3) obtained blinding of assessors of the main outcomes. We identified 819 articles, with 472 (58%) describing the method of blinding. Methods to establish blinding of patients and/or health care providers concerned mainly treatments provided in identical form, specific methods to mask some characteristics of the treatments (e.g., added flavor or opaque coverage), or use of double dummy procedures or simulation of an injection. Methods to avoid unblinding of patients and/or health care providers involved use of active placebo, centralized assessment of side effects, patients informed only in part about the potential side effects of each treatment, centralized adapted dosage, or provision of sham results of complementary investigations. The methods reported for blinding outcome assessors mainly relied on a centralized assessment of complementary investigations, clinical examination (i.e., use of video, audiotape, or photography), or adjudication of clinical events. CONCLUSIONS: This review classifies blinding methods and provides a detailed description of methods that could help trialists overcome some barriers to blinding in clinical trials and readers interpret the quality of pharmacologic trials.

Double-Blind Method↗

PubMed2005

A priori postulated and real power in cluster randomized trials: mind the gap.

BACKGROUND: Cluster randomization design is increasingly used for the evaluation of health-care, screening or educational interventions. The intraclass correlation coefficient (ICC) defines the clustering effect and be specified during planning. The aim of this work is to study the influence of the ICC on power in cluster randomized trials. METHODS: Power contour graphs were drawn to illustrate the loss in power induced by an underestimation of the ICC when planning trials. We also derived the maximum achievable power given a specified ICC. RESULTS: The magnitude of the ICC can have a major impact on power, and with low numbers of clusters, 80% power may not be achievable. CONCLUSION: Underestimating the ICC during planning cluster randomized trials can lead to a seriously underpowered trial. Publication of a priori postulated and a posteriori estimated ICCs is necessary for a more objective reading: negative trial results may be the consequence of a loss of power due to a mis-specification of the ICC.

Cluster Analysis↗

PubMed2004

Management of acute asthma exacerbations by general practitioners: a cross-sectional observational survey.

BACKGROUND: General practitioners (GPs) have a central place in the management of asthma, particularly in the context of acute exacerbations. AIM: To evaluate the management of asthma exacerbations by GPs, and to investigate the ability of risk factors for near fatal asthma to predict the severity of asthma attacks in the community. DESIGN OF STUDY: A 1-month multicentre cross-sectional survey. SETTING: One thousand and ninety-four GPs of the French Sentinel Network were contacted; 365 responded. METHOD: Asthma exacerbations were classified according to severity at presentation. Univariate and multivariate analyses were performed by logistic regression to identify those factors associated with severe exacerbations. RESULTS: Exacerbations were described in 219 patients with asthma. Over half (54%) of exacerbations were severe. Peak expiratory flow was recorded during the consultation in 55% of patients who were more than 5 years old. beta(2) agonists were prescribed to 93% of patients, systemic corticosteroids to 71%, and antibiotics to 64%. Only 42% of patients had a written action plan for self-management of exacerbations. Risk factors for near fatal asthma, identified in 26% of patients, were not significantly associated with severe asthma exacerbations. Short duration of exacerbation before consultation (<3 hours) was associated with an increase in relative risk of severe exacerbation of 3.38, 95% confidence intervals (CIs) = 1.19 to 9.61, compared with duration of >3 hours. CONCLUSION: Risk factors for near fatal asthma identified in previous studies were not predictive of a severe exacerbation in general practice, with the exception of short duration of exacerbation before consultation. This suggests that new methods to predict risk in the outpatient settings should be developed.

Acute Disease↗