On The Finite-Sample Performance Of The Nearest-Neighbor Classifier

The finite sample performance of a nearest neighbor classifier is analyzed for a two-class pattern recognition problem. An exact integral expression is derived for the m-sample risk R(m) given that a reference m-sample of labeled points is available to the classifier. The statistical setup assumes that the pattern classes arise in nature with fixed a priori probabilities and that points representing the classes are drawn from Euclidean n-space according to fixed class-conditional probability distributions. The sample is assumed to consist of m independently generated class-labeled points. For a family of smooth class-conditional distributions characterized by asymptotic expansions in general form, it is shown that the m-sample risk R(m) has a complete asymptotic series expansio

Sustainable soil management options for Malawi: can smallholder farmers grow more legumes?

Sole-cropped, unfertilized maize is the dominant cropping system throughout southern Africa. Yields have become stagnant and legumes are frequently advocated as an affordable option for resource poor farmers, to enhance productivity. Farmer participatory research was employed to test legume intensification as a means to improve maize-based systems in Malawi. A range of options were evaluated, from grain/legume intercrops of long-duration pigeonpea (Cajanus cajan) and groundnut (Arachis hypogaea) rotated with maize (Zea mays), to a relay green manure system of maize with Tephrosia vogelii. Two years of on-farm experimentation indicated that under on-farm conditions legume-intensified systems produced residues that contained ~50 kg N/ha per year, two-fold higher than sole-cropped maize residues. Grain yields from legume-intensified systems were comparable to yields from continuous sole maize, even in a dry lakeshore ecology. These preliminary findings were linked to farmer assessment, where farmers participating in the trials expressed strong interest in the technologies. Yet the probability of adoption remains uncertain. Associated surveys outlined constraints and trade-offs underlying technology choice, information that is not usually considered in conjunction with on-farm trials. Although the legumes were highly productive, farmers expressed worries about the marginal loss of maize production. While the trial performance was similar across regions, differences in market condition, farm resources and household composition appears to stimulate different technology choices. Farmers weigh the benefits of weed suppression and potential cash earnings, against the costs of seed, problems of seed access, labour requirements and problems of grain market access and price. Surveyed farmers commonly manage residues by burning. Promotion and experimentation with more efficient use of legume residues may offer higher short-term impacts than efforts to promote adoption of another cash crop. Ultimately, adoption and soil fertility benefits may depend on market returns to legume production. This study documents the value of researchers and farmers partnering in evaluation of technologies, adoption constraints and competing technology choices

Participatory, agroecological and gender-sensitive approaches to improved nutrition : a case study in Malawi

This paper examines a long-term participatory agriculture and nutrition program in northern Malawi that successfully improved child growth, crop diversity and food security through innovative educational strategies and sustainable agriculture. The farmer-led approaches used mobilized communities to apply agroecological methods and improved child feeding practices, as well as addressing unequal gender relations. Efforts to link agriculture to child health outcomes took time: 3 years before the goal was realized, with application of interdisciplinary approaches