Home About us Contact
|
Home About us Contact | ||
|
|
||
Meta-analytical Techniques (meta-analytical + techniques)
Selected AbstractsVariable reporting and quantitative reviews: a comparison of three meta-analytical techniquesECOLOGY LETTERS, Issue 5 2003Marc J. Lajeunesse Abstract Variable reporting of results can influence quantitative reviews by limiting the number of studies for analysis, and thereby influencing both the type of analysis and the scope of the review. We performed a Monte Carlo simulation to determine statistical errors for three meta-analytical approaches and related how such errors were affected by numbers of constituent studies. Hedges'd and effect sizes based on item response theory (IRT) had similarly improved error rates with increasing numbers of studies when there was no true effect, but IRT was conservative when there was a true effect. Log response ratio had low precision for detecting null effects as a result of overestimation of effect sizes, but high ability to detect true effects, largely irrespective of number of studies. Traditional meta-analysis based on Hedges'd are preferred; however, quantitative reviews should use various methods in concert to improve representation and inferences from summaries of published data. [source] Enabling regional management in a changing climate through Bayesian meta-analysis of a large-scale disturbanceGLOBAL ECOLOGY, Issue 3 2010M Aaron MacNeil ABSTRACT Aim, Quantifying and predicting change in large ecosystems is an important research objective for applied ecologists as human disturbance effects become increasingly evident at regional and global scales. However, studies used to make inferences about large-scale change are frequently of uneven quality and few in number, having been undertaken to study local, rather than global, change. Our aim is to improve the quality of inferences that can be made in meta-analyses of large-scale disturbance by integrating studies of varying quality in a unified modelling framework that is informative for both local and regional management. Innovation, Here we improve conventionally structured meta-analysis methods by including imputation of unknown study variances and the use of Bayesian factor potentials. The approach is a coherent framework for integrating data of varying quality across multiple studies while facilitating belief statements about the uncertainty in parameter estimates and the probable outcome of future events. The approach is applied to a regional meta-analysis of the effects of loss of coral cover on species richness and the abundance of coral-dependent fishes in the western Indian Ocean (WIO) before and after a mass bleaching event in 1998. Main conclusions, Our Bayesian approach to meta-analysis provided greater precision of parameter estimates than conventional weighted linear regression meta-analytical techniques, allowing us to integrate all available data from 66 available study locations in the WIO across multiple scales. The approach thereby: (1) estimated uncertainty in site-level estimates of change, (2) provided a regional estimate for future change at any given site in the WIO, and (3) provided a probabilistic belief framework for future management of reef resources at both local and regional scales. [source] Do arthropod assemblages display globally consistent responses to intensified agricultural land use and management?GLOBAL ECOLOGY, Issue 5 2008S. J. Attwood ABSTRACT Aim, To determine whether arthropod richness and abundance for combined taxa, feeding guilds and broad taxonomic groups respond in a globally consistent manner to a range of agricultural land-use and management intensification scenarios. Location, Mixed land-use agricultural landscapes, globally. Methods, We performed a series of meta-analyses using arthropod richness and abundance data derived from the published literature. Richness and abundance were compared among land uses that commonly occur in agricultural landscapes and that represent a gradient of increasing intensification. These included land-use comparisons, such as wooded native vegetation compared with improved pasture, and a management comparison, reduced-input cropping compared with conventional cropping. Data were analysed using three different meta-analytical techniques, including a simple vote counting method and a formal fixed-effects/random-effects meta-analysis. Results, Arthropod richness was significantly higher in areas of less intensive land use. The decline in arthropod richness was greater between native vegetation and agricultural land uses than among different agricultural land uses. These patterns were evident for all taxa combined, predators and decomposers, but not herbivorous taxa. Overall, arthropod abundance was greater in native vegetation than in agricultural lands and under reduced-input cropping compared with conventional cropping. Again, this trend was largely mirrored by predators and decomposers, but not herbivores. Main conclusions, The greater arthropod richness found in native vegetation relative to agricultural land types indicates that in production landscapes still containing considerable native vegetation, retention of that vegetation may well be the most effective method of conserving arthropod biodiversity. Conversely, in highly intensified agricultural landscapes with little remaining native vegetation, the employment of reduced-input crop management and the provision of relatively low-intensity agricultural land uses, such as pasture, may prove effective in maintaining arthropod diversity, and potentially in promoting functionally important groups such as predators and decomposers. [source] The Efficacy of Acamprosate in the Maintenance of Abstinence in Alcohol-Dependent Individuals: Results of a Meta-AnalysisALCOHOLISM, Issue 1 2004Karl Mann Abstract: Background: A number of clinical trials have been undertaken to determine the efficacy of acamprosate in the maintenance of abstinence in alcohol-dependent individuals. However, the reported differences in patient populations, treatment duration, and study endpoints make comparisons difficult. An assessment of the efficacy of treatment with acamprosate was, therefore, undertaken using meta-analytical techniques. Methods: All randomized, placebo-controlled trials (RCTs) that fulfilled predetermined criteria were identified using (1) a language unrestricted search of 10 electronic databases; (2) a manual search of relevant journals, symposia, and conference proceedings; (3) cross-referencing of all identified publications; (4) personal communications with investigators; and (5) scrutiny of Merck-Santé's internal reports of all European trials. Study quality was assessed, independently, by three blinded workers. Key outcome data were identified; some outcome variables were recalculated to ensure consistency across trials. The primary outcome measure was continuous abstinence at 6 months; abstinence rates were determined by estimating Relative Benefit (RB). Results: A total of 19 published 1 unpublished RCTs were identified that fulfilled the selection criteria; 3 were excluded because the documentation available was insufficient to allow adequate assessment. The remaining 17 studies, which included 4087 individuals, 53% of whom received active drug, were of good quality and were otherwise reasonably comparable. There was no evidence of publication bias. Continuous abstinence rates at 6 months were significantly higher in the acamprosate-treated patients (acamprosate, 36.1%; placebo, 23.4%; RB, 1.47; [95% confidence intervals (CI): 1.29,1.69]; p < 0.001). This effect was observed independently of the method used for assigning missing data. The effect sizes in abstinent rates at 3, 6, and 12 months were 1.33, 1.50, and 1.95, respectively. At 12 months, the overall pooled difference in success rates between acamprosate and placebo was 13.3% (95% CI, 7.8,18.7%; number needed to treat, 7.5). Acamprosate also had a modest but significant beneficial effect on retention (6.01%; [95% CI, 2.90,8.82]; p= 0.0106). Conclusion:: Acamprosate has a significant beneficial effect in enhancing abstinence in recently detoxified, alcohol-dependent individuals. [source] A comparison of segmental vs subtotal/total colectomy for colonic Crohn's disease: a meta-analysisCOLORECTAL DISEASE, Issue 2 2006P. P. Tekkis Abstract Objective, Using meta-analytical techniques the present study evaluated differences in short-term and long-term outcomes of adult patients with colonic Crohn's disease who underwent either colectomy with ileorectal anastomosis (IRA) or segmental colectomy (SC). Methods, Comparative studies published between 1988 and 2002, of subtotal/total colectomy and ileorectal anastomosis vs segmental colectomy, were used. The study end points included were surgical and overall recurrence, time to recurrence, postoperative morbidity and incidence of permanent stoma. Random and fixed-effect meta-analytical models were used to evaluate the study outcomes. Sensitivity analysis, funnel plot and meta-regressive techniques were carried out to explain the heterogeneity and selection bias between the studies. Results, Six studies, consisting of a total of 488 patients (223 IRA and 265 SC) were included. Analysis of the data suggested that there was no significant difference between IRA and SC in recurrence of Crohn's disease. Time to recurrence was longer in the IRA group by 4.4 years (95% CI: 3.1,5.8), P < 0.001. There was no difference between the incidence of postoperative complications (OR = 1.4., 95% CI 0.16,12.74) or the need for a permanent stoma between the two groups (OR = 2.75, 95% CI 0.78,9.71). Patients with two or more colonic segments involved were associated with lower re-operation rate in the IRA group, a difference which did not reach statistical significance (P = 0.177). Conclusions, Both procedures were equally effective as treatment options for colonic Crohn's disease however, patients in the SC group exhibited recurrence earlier than those in the IRA group. The choice of operation is dependent on the extent of colonic disease, with a trend towards better outcomes with IRA for two or more colonic segments involved. Since no prospective randomised study has been undertaken, a clear view about which approach is more suitable for localised colonic Crohn's disease cannot be obtained. [source] | |||||||||||||