Some new aspects of taxicab correspondence analysis

Correspondence analysis (CA) and nonsymmetric correspondence analysis are based on generalized singular value decomposition, and, in general, they are not equivalent. Taxicab correspondence analysis (TCA) is a \(\hbox {L}_{1}\) variant of CA, and it is based on the generalized taxicab singular value decomposition (GTSVD). Our aim is to study the taxicab variant of nonsymmetric correspondence analysis. We find that for diagonal metric matrices GTSVDs of a given data set are equivalent; from which we deduce the equivalence of TCA and taxicab nonsymmetric correspondence analysis. We also attempt to show that TCA stays as close as possible to the original correspondence matrix without calculating a dissimilarity (or similarity) measure between rows or columns. Further, we discuss some new geometric and distance aspects of TCA.     

Testing sphericity using small samples

It is shown here that with small sample sizes, the null distribution of the ellipticity, or sphericity, likelihood criterion W(n, p) can be obtained very accurately, either by computation using the Meijer function, or by Monte Carlo simulation. Testing in repeated measures design can now be carried out with much more accuracy.     

Statistical Discrimination Analysis Using the Maximum Function

The maximum of k functions defined on R ⁿ , n ≥ 1, by f _max (x) = max{f ₁ (x),…, f _k (x)}, ? x ? R ⁿ , can have important roles in Statistics, particularly in Classification. Through its relation with the Bayes error, which is the reference error in classification, it can serve to compute numerical bounds for errors in other classification schemes. It can also serve to define the joint L¹-distance between more than two densities, which, in turn, will serve as a useful tool in Classification and Cluster Analyses. It has a vast potential application in digital image processing too. Finally, its versatile role can be seen in several numerical examples, related to the analysis of Fisher's classical iris data in multidimensional spaces.     

Bayesian analysis of the difference of two proportions

In this article we give the expression of the prior distribution of p₁-P₂, where P₁ and P₂ and independent proportions with a beta prior each. The expression derived for the posterior distribution of P₁-P₂ then shows the closure of the beta-difference family for independent dual Bernoulli samples. Other bayesian results are also presented.     

Negotiating Compliance: The Case of Autonomous Hospitals in Vietnam

Maternal death is one of the highest causes of global mortality. Governments have long used regulation to improve maternal health but concurrent fiscal‐decentralisation reforms can undermine clinical performance. This article focuses on public Vietnamese hospitals to explore how regulatory compliance is pursued in decentralised health facilities, since Vietnam has seen increasing autonomisation of public hospitals in the last decade while simultaneously experiencing marked reductions in the maternal mortality ratio. Our analysis suggests that autonomisation has allowed regional regulatory regimes to emerge and that regulatory compliance must compete with other priorities. Compliance can therefore be rethought as a negotiation having implications for how government and maternal health advocates persuade self‐sufficient hospitals to take on wider health‐system goals.     

Where's the Farmer? Limiting Liability in Midwestern Industrial Hog Production

Scholars largely assume that hog production is following the same industrialization process as the integrated poultry industry. Since the collapse of hog farming in the 1990s, academics have anticipated that producers will eventually become trapped in contracts that leave the integrator with full control over the production process. Embedded in this prediction is an assumption that hog farmers respond to these productive pressures individually. Our analysis of the Carthage Management System suggests a different path for the hog commodity chain. The Carthage Management System is a conglomeration of business management firms that bring finishing hog farmers together to form limited liability corporations (LLCs) in the breed‐to‐wean stage of hog production. We use a sociology of agrifood framework to suggest that the nuances of hog production encourage the use of what we call folding corporations to limit liability in ways that profoundly transform the family farm. Corporations and individual hog farmers alike employ this creative LLC structure to deflect responsibility for the risks of hog production. We identify how folding corporations externalize the costs of production onto rural communities. Additional research is needed to better understand unfolding farmer identities, legal protections for farmers, how widespread organizational structures like Carthage Management System are, and their consequences for rural communities and the industrialization process.     

Value of the beta prior information

Information gain or loss is studied here by considering changes in the reciprocal of the expected posterior variance. For two beta distributions, the ratio of the expected values of their posterior variances provides a convenient criterion which is consistent with several results of the bayesian set-up and also permits the determination of the least informative prior beta distribution. Relations with results obtained by other authors are also discussed.     

A modified two-stage approach for joint modelling of longitudinal and time-to-event data

Joint models for longitudinal and time-to-event data have been applied in many different fields of statistics and clinical studies. However, the main difficulty these models have to face with is the computational problem. The requirement for numerical integration becomes severe when the dimension of random effects increases. In this paper, a modified two-stage approach has been proposed to estimate the parameters in joint models. In particular, in the first stage, the linear mixed-effects models and best linear unbiased predictorsare applied to estimate parameters in the longitudinal submodel. In the second stage, an approximation of the fully joint log-likelihood is proposed using the estimated the values of these parameters from the longitudinal submodel. Survival parameters are estimated bymaximizing the approximation of the fully joint log-likelihood. Simulation studies show that the approach performs well, especially when the dimension of random effects increases. Finally, we implement this approach on AIDS data.     

Design optimisation for pharmacokinetic modeling of a cocktail of phenotyping drugs

Our paper proposes a methodological strategy to select optimal sampling designs for phenotyping studies including a cocktail of drugs. A cocktail approach is of high interest to determine the simultaneous activity of enzymes responsible for drug metabolism and pharmacokinetics, therefore useful in anticipating drug–drug interactions and in personalized medicine. Phenotyping indexes, which are area under the concentration‐time curves, can be derived from a few samples using nonlinear mixed effect models and maximum a posteriori estimation. Because of clinical constraints in phenotyping studies, the number of samples that can be collected in individuals is limited and the sampling times must be as flexible as possible. Therefore to optimize joint design for several drugs (i.e., to determine a compromise between informative times that best characterize each drug's kinetics), we proposed to use a compound optimality criterion based on the expected population Fisher information matrix in nonlinear mixed effect models. This criterion allows weighting different models, which might be useful to take into account the importance accorded to each target in a phenotyping test. We also computed windows around the optimal times based on recursive random sampling and Monte‐Carlo simulation while maintaining a reasonable level of efficiency for parameter estimation. We illustrated this strategy for two drugs often included in phenotyping cocktails, midazolam (probe for CYP3A) and digoxin (P‐glycoprotein), based on the data of a previous study, and were able to find a sparse and flexible design. The obtained design was evaluated by clinical trial simulations and shown to be efficient for the estimation of population and individual parameters. Copyright © 2015 John Wiley & Sons, Ltd.     

Organic coasts? Regulatory challenges of certifying integrated shrimp–mangrove production systems in Vietnam

The Vietnamese government aims to expand the scale of Naturland certified organic production in integrated shrimp–mangrove farming systems across the coast of Ca Mau province by 2015. In doing so the division between public and private regulation has become blurred. We analyze the government's goal by examining the regulatory challenges of using organic certification as a means of linking farm-level management to the sustainability of coastal (mangrove) landscapes. The results show the importance of farmer perceptions of sustainable farm and landscape management, fair benefit sharing mechanisms in the certified value chain, and legitimate private sector-led auditing. We conclude that in order to overcome conflicts of interest and legitimate representation in organic certification, the social and economic conditions of production require regulatory intervention from provincial and local level government. To achieve benefits beyond the scale of the farm, the role of shrimp producers should be redefined as partners in rather than targets of regulation.