STATISTICA & APPLICAZIONI - 2008 - 2 - autori-vari - Vita e Pensiero - Fascicolo digitale Statistica & Applicazioni


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Issue 2 - 2008
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Minimum sample sizes in asymptotic confidence intervals for Gini’s inequality measure
by Francesca Greselin, Leo Pasquazzi pages: 17 Download
Statistical inference for inequality measures has been of considerable interest in recent years. Income studies often deal with very large samples, hence precision would not seem a serious issue. Yet, in many empirical studies large standard errors are observed (Maasoumi, 1997). Therefore, it is important to provide methodologies to assess whether differences in estimates are statistically significant. This paper presents an analysis of the performance of asymptotic confidence intervals for Gini’s index, virtually the most widely used inequality index. To determine minimum sample sizes assuring a given accuracy in confidence intervals, an extensive simulation study has been carried out. A wide set of underlying distributions has been considered, choosing from specific models for income data. As expected, the minimum sample sizes are seriously affected by some population characteristics as tail heaviness and asymmetry. However, in a wide range of cases, it turns out that they are smaller than sample sizes actually used in social sciences.
A Subgroups Decomposition of Zenga’s Uniformity and Inequality indexes
by Paolo Radaelli pages: 20 Download
We propose a subgroups decomposition of the uniformity index recently introduced by Zenga [2007]. The decomposition scheme adopted follows the structure of the index which is based on the ratios between lower and upper arithmetic means. The keypoint is the evaluation of the point uniformity index both within the same subgroup and between two different subgroups. The decomposition obtained for the uniformity index is finally applied to achieve an analogous decomposition of the inequality index.
The continuous random variable with uniform point inequality measure
by Marcella Polisicchio pages: 15 Download
By using the conditions that the expected value of an absolute random variable X is finite and positive and that the point inequality measure I ðpÞ is uniform for 0 < p < 1, this paper discusses the question of the existence of such random variable and proves that this problem has a unique solution. The obtained cumulative distribution function of X is a truncated Pareto distribution, with traditional inequality parameter equal to 0,5 and with support depending on the finite and positive expected value and the level of uniformity, based on the ratios between the lower means and the upper means, used for defining the point inequality measure I(p).
A symbolic data approach for missing values treatment in principal component analysis
by Paola Zuccolotto pages: 28 Download
There are two ways in order to completely perform a Principal Component Analysis over a data table with missing values: somehow imputating values to the missing data or excluding some part of the original sample from the analysis. Both these solutions can be rather costly, expecially with datasets having an appreciable number of missing values, but only one or at most two missing on any particular observational unit. An alternative proposal is formulated in this paper using the concept of Symbolic Data.
Estimation of power function distribution with application to ecological relative abundance
by N.A. Al-Odat, Mohd T. Alodat, H. Beldjillali, R.A. Muhaidat pages: 12 Download
In this paper we derive Bayesian and non-Bayesian estimators for the parameter of the power function distribution, and prediction intervals for the maximum of a future sample. We apply our approach to field data of plant species relative abundance, the abundance of a given species divided by the total abundance of all plant species in given a community, collected in a biodiversity project in central Europe.
Measuring loan recovery rate: methodology and empirical evidence
by Raffaella Calabrese, Michele Zenga pages: 22 Download
This paper aims at proposing a new methodology to compute recovery rate on non-performing bank loans, in order to confine this variable within the interval [0,1]. Such a methodology is then applied to data on loans gathered by the Bank of Italy and some interesting characteristics of the loan recovery process in the Italian banking market are highlighted. The combined effects of some variables on the recovery rates are also analysed. In particular, the presence of either collateral or personal guarantee, the borrower’s residence area are considered, thereby emphasizing the relationship between the recovery rate and the total exposure.
A definition of neighborhoods based on Local Labor Systems: a regional application on employment data
by Pamela Mason, Gian Pietro Zaccomer pages: 22 Download
The singling out of a neighborhood is often a critical point when we wish to employ one of the tools proposed by spatial statistics. In fact this is directly correlated to the researcher’s hypothesis on how interactions among territorial units affect the performances of the phenomenon under examination. The aim of this article is to compare results obtained by different shift-share decompositions related to the annual variation of regional employment in Friuli Venezia Giulia. Many of the different spatial weights matrices proposed by literature are here taken into consideration. As in other contexts, in this paper the interpretation of neighborhood is fundamental. Therefore, we introduce a specific method to create a neighborhood in order to assign it an explicit territorial meaning.
Errata corrige
pages: 1 Download
STATISTICA & APPLICAZIONI, VOL. IV, Numero Speciale 2, 2006 We regret a mispelling error of the author name Kadarmanto on the cover page, table of contents and Editorial (page 3). Our apologies to the author.

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