A case study of an individual participant data meta-analysis of diagnostic accuracy showed that prediction regions represented heterogeneity well

The diagnostic accuracy of a screening tool is often characterized by its sensitivity and specificity. An analysis of these measures must consider their intrinsic correlation. In the context of an individual participant data meta-analysis, heterogeneity is one of the main components of the analysis. When using a random-effects meta-analytic model, prediction regions provide deeper insight into the effect of heterogeneity on the variability of estimated accuracy measures across the entire studied population, not just the average. This study aimed to investigate heterogeneity via prediction regions in an individual participant data meta-analysis of the sensitivity and specificity of the Patient Health Questionnaire-9 for screening to detect major depression. From the total number of studies in the pool, four dates were selected containing roughly 25%, 50%, 75% and 100% of the total number of participants. A bivariate random-effects model was fitted to studies up to and including each of these dates to jointly estimate sensitivity and specificity. Two-dimensional prediction regions were plotted in ROC-space. Subgroup analyses were carried out on sex and age, regardless of the date of the study. The dataset comprised 17,436 participants from 58 primary studies of which 2322 (13.3%) presented cases of major depression. Point estimates of sensitivity and specificity did not differ importantly as more studies were added to the model. However, correlation of the measures increased. As expected, standard errors of the logit pooled TPR and FPR consistently decreased as more studies were used, while standard deviations of the random-effects did not decrease monotonically. Subgroup analysis by sex did not reveal important contributions for observed heterogeneity; however, the shape of the prediction regions differed. Subgroup analysis by age did not reveal meaningful contributions to the heterogeneity and the prediction regions were similar in shape. Prediction intervals and regions reveal previously unseen trends in a dataset. In the context of a meta-analysis of diagnostic test accuracy, prediction regions can display the range of accuracy measures in different populations and settings

Farmers' knowledge and management of spatial soil and crop growth variability in Niger, West Africa

A household survey conducted in the Sahel, combined with an extensive literature search of baseline studies, complemented on-station research on spatial soil and crop growth variability from a farmers viewpoint. Farmers explained spatial variability in crop growth in terms of differences in soil types, soil fertility and degradation, as well as their cultivation and management practices. Farmers counteract spatial crop growth variability by within-field fallow; kraaling; spot applications of manure, crop residues and household waste; by intentionally moving their settlements; and by exploiting the micro-environmental differences around specific tree and shrub species. However, these strategies also enforce the spatial crop growth variability. The accuracy of farmers' comprehensive knowledge of agriculture, soil, animal husbandry and agro-forestry was confirmed by compartmentalized on-farm and on-station studies conducted in the same region, although explanations of farmers and researchers were not always the same. Farmers are aware of soil fertility management technologies, either coming from outside or developed within the farming community, but are often unable to translate these into action on a large scale. This is due to insufficient resources and socioeconomic, as well as institutional, constraints such as cattle ownership, land tenure, labour requirements and prices of inputs. Implications for agricultural research and technology generation are discussed

Economic incentives for adopting irrigation innovations in arid environments

Water is getting scarce in many parts of the world, consequently challenging researchers, policy makers and practitioners to design options for a more efficient use of these resources, especially in irrigated agriculture. Although technical-economic efficiency of potential water-wise options and institutional restrictions for their implementation in the developing and less-developed countries are well documented, little evidence exists about the incentives for farmers and regional development agencies to adopt the efficient irrigation innovations. A linear programming model for optimizing regional agricultural income was developed to analyze the impact of water availability, water pricing, and investment accessibility on water-wise innovation adoption and conveyance efficiency improvement. The model was applied to the case of Khorezm, a region in northwestern Uzbekistan that is part of the downstream Amu Darya River in the Aral Sea Basin. Model results indicate that improving conveyance efficiency is economically less attractive than improving field-level water use efficiency due to enormous investment costs for lining the canals. Water-wise options such as manuring cotton and potatoes, implementing hydrogel in wheat and cotton, and drip irrigation of melons and vegetables are among the most promising field-level improvement options to gain optimal regional incomes under decreased water availability and increased water prices. It is illustrated that despite the huge investments needed for a wide-scale implementation of modern irrigation technologies such as drip irrigation and laser-guided land leveling, their adoption will substantially improve water use efficiency, while their implementation costs can be compensated for by the additional revenues due to increased yields and reduced costs

Coping with water scarcity in the irrigated lowlands of the lower Amudarya basin, Central Asia

Improving irrigation efficiency is of utmost importance in the irrigated lands of Central Asia, such as the Khorezm region of Uzbekistan, since water misuse and subsequent soil salinization threaten environment, economy, and livelihoods. To this end, several field-level ‘water-wise’ innovations were selected, which are classified into four groups that address crop pattern change, soil moisture maintenance, uniform water distribution, and furrow irrigation improvement. The potential of these innovations to raise irrigation water use efficiency from its current low level was analyzed from a socio-economic and technical point of view with a focus on short-term measures to cope with sudden water shortages. The overall water use reduction potential of these options was estimated considering their adoption feasibility within the time horizon of one year. To prioritize the examined innovations according to their contribution to overall water use reduction and water profitability, ‘marginal water profitability curves’ were developed. This integrated approach could serve as a simple but effective policy tool. The findings indicate that the option of replacing rice by maize contributes to more than 50 % of the total possible water use reduction. However, while all the other options increase the total revenue, reduced revenues will be unavoidable when paddy rice is replaced by maize. Manuring provides the highest additional profit per volume of reduced water use, but contributes less than 10 % of the total water use reduction potential. With water-wise options as an immediate and short-term measure to cope with sudden water shortages, the theoretical total estimated water reduction at the field level amounts to 183 – 376,000,000 m3 or 9.0 – 18.5 % of the current total irrigation water requirement in the region. For coping with sudden shortages characterized by a water availability of only 60 % of the normal water supply, long-term planning and management of irrigation activities focusing on a wider adoption of advanced irrigation technologies are necessary

Harnessing renewable energy from abandoned salt-affected lands and saline drainage networks in the dry areas

In El-Beltagy, A.; Saxena, M. C. (Eds.). Sustainable development in drylands: meeting the challenge of global climate change. Proceedings of the Ninth International Conference on Development of Drylands, Alexandria, Egypt, 7-10 November 2008. Theme 8 - Reducing greenhouse gas emission through harnessing renewable energy in the dry areas. Giza, Cairo, Egypt: International Dryland Development Commission (IDDC)

Integrating input-output modeling with multi-criteria analysis to assess options for sustainable economic transformation: the case of Uzbekistan

Integrating economic efficiency and environmental sustainability indicators is essential for designing policies for a sustainable development. Given the growing pressure on water resources, efficient water use becomes an essential environmental criteria for formulating adjustment reforms. Despite the wide use of backward and forward linkages as well as direct and indirect resource (energy, water, etc.) uses based on environmentally extended input-output models for assessing the performance of economic sectors, the common practice of presenting different indicators separately obstructed a straightforward policy interpretation of results. To derive a composite indicator that allows to direct ranking of sectors, we combined therefore a direct and indirect water use intensities with backward and forward linkage indexes by using the multi-criteria analysis method-TOPSIS (Technique for order preference by similarity to ideal solution). The model was implemented to formulate sectoral transformation measures guided by sustainable growth objectives in Uzbekistan, Central Asia, which is a representative of an area with growing water scarcity. The results showed that the presently promoted crops under the state order system—cotton and wheat—and crop preferred by farmers— rice—are the least effective production options for reaching such a sustainable growth. It is argued therefore that unbiased support for all crops through adaption of the current state order system for cotton and wheat cultivation is needed to achieve a more diversified crop portfolio with an increased share of fruits and vegetables. A further development of agro-processing industries and livestock sector bears more potential for sustainable economic development than a further promotion of producing raw agricultural commodities. Investing in industrial sectors illustrated more potential than in agriculture related sectors when aiming at economic effectiveness and increased water use efficiency. It is concluded that, with a relevant sectoral transformation, Uzbekistan has high opportunities to cope with reduced water availability