The contributions of rare objects in correspondence analysis

Correspondence analysis, when used to visualize relationships in a table of counts(for example, abundance data in ecology), has been frequently criticized as being too sensitiveto objects (for example, species) that occur with very low frequency or in very few samples. Inthis statistical report we show that this criticism is generally unfounded. We demonstrate this inseveral data sets by calculating the actual contributions of rare objects to the results ofcorrespondence analysis and canonical correspondence analysis, both to the determination ofthe principal axes and to the chi-square distance. It is a fact that rare objects are oftenpositioned as outliers in correspondence analysis maps, which gives the impression that theyare highly influential, but their low weight offsets their distant positions and reduces their effecton the results. An alternative scaling of the correspondence analysis solution, the contributionbiplot, is proposed as a way of mapping the results in order to avoid the problem of outlying andlow contributing rare objects.

Asymptotic robust inferences in the analysis of mean and covariance structures

Structural equation models are widely used in economic, socialand behavioral studies to analyze linear interrelationships amongvariables, some of which may be unobservable or subject to measurementerror. Alternative estimation methods that exploit different distributionalassumptions are now available. The present paper deals with issues ofasymptotic statistical inferences, such as the evaluation of standarderrors of estimates and chi--square goodness--of--fit statistics,in the general context of mean and covariance structures. The emphasisis on drawing correct statistical inferences regardless of thedistribution of the data and the method of estimation employed. A(distribution--free) consistent estimate of $\Gamma$, the matrix ofasymptotic variances of the vector of sample second--order moments,will be used to compute robust standard errors and a robust chi--squaregoodness--of--fit squares. Simple modifications of the usual estimateof $\Gamma$ will also permit correct inferences in the case of multi--stage complex samples. We will also discuss the conditions under which,regardless of the distribution of the data, one can rely on the usual(non--robust) inferential statistics. Finally, a multivariate regressionmodel with errors--in--variables will be used to illustrate, by meansof simulated data, various theoretical aspects of the paper.

Power transformations in correspondence analysis

Power transformations of positive data tables, prior to applying the correspondence analysis algorithm, are shown to open up a family of methods with direct connections to the analysis of log-ratios. Two variations of this idea are illustrated. The first approach is simply to power the original data and perform a correspondence analysis this method is shown to converge to unweighted log-ratio analysis as the power parameter tends to zero. The second approach is to apply the power transformation to thecontingency ratios, that is the values in the table relative to expected values based on the marginals this method converges to weighted log-ratio analysis, or the spectral map. Two applications are described: first, a matrix of population genetic data which is inherently two-dimensional, and second, a larger cross-tabulation with higher dimensionality, from a linguistic analysis of several books.

Statistics in archaeology: New directions

Connections between Statistics and Archaeology have always appeared veryfruitful. The objective of this paper is to offer an outlook of somestatistical techniques that are being developed in the most recentyears and that can be of interest for archaeologists in the short run.

Distributional equivalence and subcompositional coherence in the analysis of contingency tables, ratio-scale measurements and compositional data

We consider two fundamental properties in the analysis of two-way tables of positive data: the principle of distributional equivalence, one of the cornerstones of correspondence analysis of contingency tables, and the principle of subcompositional coherence, which forms the basis of compositional data analysis. For an analysis to be subcompositionally coherent, it suffices to analyse the ratios of the data values. The usual approach to dimension reduction in compositional data analysis is to perform principal component analysis on the logarithms of ratios, but this method does not obey the principle of distributional equivalence. We show that by introducing weights for the rows and columns, the method achieves this desirable property. This weighted log-ratio analysis is theoretically equivalent to spectral mapping , a multivariate method developed almost 30 years ago for displaying ratio-scale data from biological activity spectra. The close relationship between spectral mapping and correspondence analysis is also explained, as well as their connection with association modelling. The weighted log-ratio methodology is applied here to frequency data in linguistics and to chemical compositional data in archaeology.

The Role of supply constraints in multiplier analysis

Multiplier analysis based upon the information contained in Leontief's inverse is undoubtedly part of the core of the input-output methodology and numerous applications an extensions have been developed that exploit its informational content. Nonetheless there are some implicit theoretical assumptions whose implications have perhaps not been fully assessed. This is the case of the 'excess capacity' assumption. Because of this assumption resources are available as needed to adjust production to new equilibrium states. In real world applications, however, new resources are scarce and costly. Supply constraints kick in and hence resource allocation needs to take them into account to really assess the effect of government policies. Using a closed general equilibrium model that incorporates supply constraints, we perform some simple numerical exercises and proceed to derive a 'constrained' multiplier matrix that can be compared with the standard 'unrestricted' multiplier matrix. Results show that the effectiveness of expenditure policies hinges critically on whether or not supply constraints are considered.

On the automatic application of inequality indexes in the analysis of the international distribution of environmental indicators

In recent years traditional inequality measures have been used to quite a considerable extent to examine the international distribution of environmental indicators. One of its main characteristics is that each one assigns different weights to the changes that occur in the different sections of the variable distribution and, consequently, the results they yield can potentially be very different. Hence, we suggest the appropriateness of using a range of well-recommended measures to achieve more robust results. We also provide an empirical test for the comparative behaviour of several suitable inequality measures and environmental indicators. Our findings support the hypothesis that in some cases there are differences among measures in both the sign of the evolution and its size. JEL codes: D39; Q43; Q56. Keywords: international environment factor distribution; Kaya factors; Inequality measurement

A fully-automatic caudate nucleus segmentation of brain MRI: application in volumetric analysis of pediatric attention-deficit/hyperactivity disorder

Background Accurate automatic segmentation of the caudate nucleus in magnetic resonance images (MRI) of the brain is of great interest in the analysis of developmental disorders. Segmentation methods based on a single atlas or on multiple atlases have been shown to suitably localize caudate structure. However, the atlas prior information may not represent the structure of interest correctly. It may therefore be useful to introduce a more flexible technique for accurate segmentations. Method We present Cau-dateCut: a new fully-automatic method of segmenting the caudate nucleus in MRI. CaudateCut combines an atlas-based segmentation strategy with the Graph Cut energy-minimization framework. We adapt the Graph Cut model to make it suitable for segmenting small, low-contrast structures, such as the caudate nucleus, by defining new energy function data and boundary potentials. In particular, we exploit information concerning the intensity and geometry, and we add supervised energies based on contextual brain structures. Furthermore, we reinforce boundary detection using a new multi-scale edgeness measure. Results We apply the novel CaudateCut method to the segmentation of the caudate nucleus to a new set of 39 pediatric attention-deficit/hyperactivity disorder (ADHD) patients and 40 control children, as well as to a public database of 18 subjects. We evaluate the quality of the segmentation using several volumetric and voxel by voxel measures. Our results show improved performance in terms of segmentation compared to state-of-the-art approaches, obtaining a mean overlap of 80.75%. Moreover, we present a quantitative volumetric analysis of caudate abnormalities in pediatric ADHD, the results of which show strong correlation with expert manual analysis. Conclusion CaudateCut generates segmentation results that are comparable to gold-standard segmentations and which are reliable in the analysis of differentiating neuroanatomical abnormalities between healthy controls and pediatric ADHD.

Flow cytometry in the analysis of cellular populations

Flow cytometry has become a valuable tool in cell biology. By analyzing large number of cells individually using light-scatter and fluorescence measurements, this technique reveals both cellular characteristics and the levels of cellular components. Flow cytometry has been developed to rapidly enumerate cells and to distinguish among different cell stages and structures using multiple staining. In addition to high-speed multiparametric data acquisition, analysis and cell sorting, which allow other characteristics of individual cells to be studied, have increased the interest of researchers in this technique. This chapter gives an overview of the principles of flow cytometry and examples of the application ofthe technique.

Heterogeneity and event dependence in the analysis of sickness absence

Sickness absence (SA) is an important social, economic and public health issue. Identifying and understanding the determinants, whether biological, regulatory or, health services-related, of variability in SA duration is essential for better management of SA. The conditional frailty model (CFM) is useful when repeated SA events occur within the same individual, as it allows simultaneous analysis of event dependence and heterogeneity due to unknown, unmeasured, or unmeasurable factors. However, its use may encounter computational limitations when applied to very large data sets, as may frequently occur in the analysis of SA duration. To overcome the computational issue, we propose a Poisson-based conditional frailty model (CFPM) for repeated SA events that accounts for both event dependence and heterogeneity. To demonstrate the usefulness of the model proposed in the SA duration context, we used data from all non-work-related SA episodes that occurred in Catalonia (Spain) in 2007, initiated by either a diagnosis of neoplasm or mental and behavioral disorders. As expected, the CFPM results were very similar to those of the CFM for both diagnosis groups. The CPU time for the CFPM was substantially shorter than the CFM. The CFPM is an suitable alternative to the CFM in survival analysis with recurrent events,especially with large databases.

The global report of trafficking in persons: analysis and results

L'Oficina de les Nacions Unides contra la Droga i el Delicte en el seu informe "Global Report on Trafficking in Persons" de 2012 recull que "l'explotació sexual és, amb gran diferència, la forma de tràfic de persones detectades amb més freqüència, concretament en xifres un total del 79 % dels casos. Enllaç a l'informe sencer: http://www.unodc.org/documents/data-and-analysis/glotip/Trafficking_in_Persons_2012_web.pdf

Final architecture diploma projects in the analysis of the UPC buildings energy performance

A partir de maig de 2003, per iniciativa del Vicerectorat adjunt d’Edificacions de la UPC, el Centre Interdisciplinari de Tecnologia, Innovació i Educació per a la Sostenibilitat (CITIES) treballa en l’elaboració i la implantació del Pla d’Eficiència en el Consum de Recursos (PECR), amb l’objectiu d’establir polítiques i definir línees d’actuació per a l’estalvi i l’eficiència en el consum dels recursos energètics i d’ aigua en els edificis de la UPC.El PECR contempla, en una de les primeres fases, la realització d’avaluacions energètiques en les edificacions de la UPC per valorar l’estat actual dels edificis i poder establir uns indicadors del seu comportament energètic a partir dels quals establir els objectius d’estalvi i d’eficiència. Per fer aquestes avaluacions, es va crear una línea de projectes finals de carrera (PFC) per a estudiants de l’Escola Politècnica Superior de l’Edificació de Barcelona (EPSEB), sota la coordinació de professors tutors de diferents departaments y amb la col•laboració indispensable de totes les unitats de recolzament de la UPC.Aquesta publicació és la ponència presentada al IV Congrès "Sustainable City", a Tallinn, en el que es va presentar aquest projecte com a una eina de treball amb l'objectiu de reduir l'impacte ambiental dels edificis universitaris en les ciutats.

The Application of 3D Reconstruction Techniques in the Analysis of Ancient Tarraco’s Urban Topography

The widespread implementation of GIS-based 3D topographical models has been a great aid in the development and testing of archaeological hypotheses. In this paper, a topographical reconstruction of the ancient city of Tarraco, the Roman capital of the Tarraconensis province, is presented. This model is based on topographical data obtained through archaeological excavations, old photographic documentation, georeferenced archive maps depicting the pre-modern city topography, modern detailed topographical maps and differential GPS measurements. The addition of the Roman urban architectural features to the model offers the possibility to test hypotheses concerning the ideological background manifested in the city shape. This is accomplished mainly through the use of 3D views from the main city accesses. These techniques ultimately demonstrate the ‘theatre-shaped’ layout of the city (to quote Vitrubius) as well as its southwest oriented architecture, whose monumental character was conceived to present a striking aspect to visitors, particularly those arriving from the sea.

Analytical challenges in breath analysis and its application to exposure monitoring

There is an increasing interest in the use of breath analysis for monitoring human physiology and exposure to toxic substances or environmental pollutants. This review focuses on the current status of the sampling procedures, collection devices and sample-enrichment methodologies used for exhaled breath-vapor analysis. We discuss the different parameters affecting each of the above steps, taking into account the requirements for breath analysis in exposure assessments and the need to analyze target compounds at sub-ppbv levels. Finally, we summarize the practical applications of exposure analysis in the past two decades