Quantifying, displaying and accounting for heterogeneity in the meta-analysis of RCTs using standard and generalised Q statistics

RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are.Abstract Background Clinical researchers have often preferred to use a fixed effects model for the primary interpretation of a meta-analysis. Heterogeneity is usually assessed via the well known Q and I2 statistics, along with the random effects estimate they imply. In recent years, alternative methods for quantifying heterogeneity have been proposed, that are based on a 'generalised' Q statistic. Methods We review 18 IPD meta-analyses of RCTs into treatments for cancer, in order to quantify the amount of heterogeneity present and also to discuss practical methods for explaining heterogeneity. Results Differing results were obtained when the standard Q and I2 statistics were used to test for the presence of heterogeneity. The two meta-analyses with the largest amount of heterogeneity were investigated further, and on inspection the straightforward application of a random effects model was not deemed appropriate. Compared to the standard Q statistic, the generalised Q statistic provided a more accurate platform for estimating the amount of heterogeneity in the 18 meta-analyses. Conclusions Explaining heterogeneity via the pre-specification of trial subgroups, graphical diagnostic tools and sensitivity analyses produced a more desirable outcome than an automatic application of the random effects model. Generalised Q statistic methods for quantifying and adjusting for heterogeneity should be incorporated as standard into statistical software. Software is provided to help achieve this aim.Published versio

Greening rubber? Political ecologies of plantation sustainability in Laos and Myanmar

Over the past decade, the cultivation of rubber trees has expanded rapidly throughout the Mekong region to non-traditional rubber growing areas of Laos and Myanmar. Prompted by rising prices from 1990 to 2010 and government agro-industrialization policies, farmers and investors have rushed to plant the new boom crop. A latex price crash in 2011, however, has made it more challenging for small-scale producers to earn an income, leading to uneven social-ecological transformations and economic consequences. Several proposals have been made to address these challenges by transforming rubber into a more economically, socially, and environmentally sustainable crop. In this paper, which emerged from one such project to investigate the potential for green rubber, we argue that the sustainability of rubber is a challenging and elusive prospect - particularly in resource frontier contexts like Laos and Myanmar. Concepts like sustainability or green production are vague and malleable. They can be imbued with a variety of contradictory meanings, which often do not address the most socially and environmentally problematic aspects of cash crop expansion. Sustainable rubber, if rigorously and specifically defined, would be exceedingly difficult to reach in both countries, due to the ways in which political-economic and governance factors interact with the biophysical and social characteristics of the crop. Instead, we recommend using sustainability as a political tool for highlighting the most harmful socio-environmental impacts of rubber and generating debate concerning the best ways to address these, thus limiting unsustainable practices.</p