Parameterized complexity of k-anonymity: hardness and tractability

The problem of publishing personal data without giving up privacy is becoming increasingly important. A precise formalization that has been recently proposed is the k-anonymity, where the rows of a table are partitioned into clusters of sizes at least k and all rows in a cluster become the same tuple after the suppression of some entries. The natural optimization problem, where the goal is to minimize the number of suppressed entries, is hard even when the stored values are over a binary alphabet or the table consists of a bounded number of columns. In this paper we study how the complexity of the problem is influenced by different parameters. First we show that the problem is W[1]-hard when parameterized by the value of the solution (and k). Then we exhibit a fixed-parameter algorithm when the problem is parameterized by the number of columns and the number of different values in any column. Finally, we prove that k-anonymity is still APX-hard even when restricting to instances with 3 columns and k=3.     

Control Premium in Legally Constrained Markets for Corporate Control: The Italian Case (1993–2003)*

We discuss the simple model pioneered by Barclay and Holderness (1989, Journal of Financial Economics 25: 371–395) and recently reproposed by Dyck and Zingales (2004a, Journal of Finance 2, 537–600; 2004b Journal of Applied Corporate Finance 16, 51–72) in order to measure the value of control in countries, like Italy, where transfer of control is regulated by law. We demonstrate that it is possible to broaden the application of B&;H approach to block trades followed by mandatory tender offers and we show the conditions under which we may obtain significant measures of private benefits also when voluntary tender offers are considered. In order to test for our theoretical predictions, we analyse the pricing of 27 control transactions involving the common stock of Italian listed corporations between 1993 and 2003. We find that block-transaction (tender) premium equals on average 8% of the firm’s equity value in the case of pure block-trades, 9% in the case of block trades followed by a mandatory tender offer, while it increases to 18% in the case of voluntary tender offers. The results suggest that, in the case of block trades followed by a mandatory tender offer, the acquirer does not transfer a larger portion of its surplus. This doesn’t take place in the case of voluntary tender offers, in which the raider’s bargaining power collapses. Our estimate of the control premium is sensibly lower than that presented in previous studies based on similar methodologies, providing up-to-date evidence for control stake valuation purposes and for comparison with cross country studies aiming at assessing the quality of rules devoted to minority shareholders’ protection. We also perform a cross-sectional regression analysis of private benefits of control and confirm some of the findings presented in the previous literature: particularly, we find evidence of a positive relation between the magnitude of private benefits of control and the target’s degree of stock-pyramiding. We also find that foreign acquirers and financial investors seem likely to face greater difficulties in extracting private benefits of control.     

The tone of business model disclosure: an impression management analysis of the integrated reports

The rising emphasis on the business model (BM) as a reportable element reflects the view that it constitutes one of the key starting points for investors’ analysis. In spite of this, recent academic and professional studies describe current reporting on BMs as uninformative: too optimistic, generic and incomplete. The International Integrated Reporting Council (IIRC) claims that these limitations may be overcome by means of an “Integrated Report”, an innovative report which is expected to offer a complete and balanced representation of how organizations create value by mean of their BMs. The paper investigates the informativeness of BM disclosure questioning whether companies adopt impression management (IM) strategies by manipulating the tone of the BM disclosures provided in their reports. We perform a manual content analysis of all the reports identified in the IIRC website and a multivariate statistical analysis to assess if a positive tone of BM disclosure is significantly associated with weak corporate governance, bad performance and low verifiability of the disclosure itself. Our findings support the idea that managers use BM disclosure as an IM strategy. This evidence has relevant implications for both accounting scholars and practitioners, since it questions the role of integrated reporting in improving corporate reporting on BMs.     

The role and significance of endogenous firing costs in a matching model with endogenous job destruction

Traditional models of the labor market assume fixed firing costs. This paper explores the implications of variable firing costs, building this new assumption into a matching model with endogenous job destruction. The available evidence on the outcomes of cases brought to labor courts suggests that firing costs are negatively related with labor market tightness. In such a case, we may no longer invoke “rigidities” on labor markets as the cause of their poor performance. Our model yields three interesting results. First, labor markets may have multiple equilibria that cannot be Pareto-ordered; each with its own configuration in terms of average duration of unemployment and filled jobs, as well as employment protection. Second, the variability of firing costs produces a positive externality affecting the stability properties of these equilibria. Finally, the two externalities affect the efficiency of the social optimum, modifying the Hosios [Hosios, A.J., 1990. On the efficiency of matching and related models of search and unemployment. Review of Economic Studies 57, 279–298] condition. We use these results to interpret the recent history of European unemployment.     

Reputational cues in repeated trust games

The importance of reputation in human societies is highlighted both by theoretical models and empirical studies. In this paper, we have extended the scope of previous experimental studies based on trust games by creating treatments where players can rate their opponents’ behavior and know their past ratings. Our results showed that being rated by other players and letting this rating be known are factors that increase cooperation levels even when rational reputational investment motives are ruled out. More generally, subjects tended to respond to reputational opportunities even when this was neither rational nor explainable by reciprocity.     

Optimal Bayesian estimators for latent variable cluster models

In cluster analysis interest lies in probabilistically capturing partitions of individuals, items or observations into groups, such that those belonging to the same group share similar attributes or relational profiles. Bayesian posterior samples for the latent allocation variables can be effectively obtained in a wide range of clustering models, including finite mixtures, infinite mixtures, hidden Markov models and block models for networks. However, due to the categorical nature of the clustering variables and the lack of scalable algorithms, summary tools that can interpret such samples are not available. We adopt a Bayesian decision theoretical approach to define an optimality criterion for clusterings and propose a fast and context-independent greedy algorithm to find the best allocations. One important facet of our approach is that the optimal number of groups is automatically selected, thereby solving the clustering and the model-choice problems at the same time. We consider several loss functions to compare partitions and show that our approach can accommodate a wide range of cases. Finally, we illustrate our approach on both artificial and real datasets for three different clustering models: Gaussian mixtures, stochastic block models and latent block models for networks.     

Reintermediating Voluntary Action: The Path-Dependent Pluralization of the Italian Volunteering Field

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations - While the international literature has significantly addressed the “new forms of voluntary action,” there has...     

An Indicator for the Measurement of Political Participation: The Case of Italy

In the modern globalized world, political participation is of paramount importance for balanced socio-economic growth and for human development. The Indagine Multiscopo sulle famiglie, a survey by Italian public institutions (ISTAT and CNEL), provides a wide range of data to evaluate specific aspects of Italian life. This work uses a set of data from the Indagine to analyse political participation in Italy at a regional level, by means of a composite indicator using parametric (Pena’s distance) and non-parametric (Mazziotta–Pareto Index) techniques. We have obtained a ranking that shows the level of political participation in different territorial contexts. The aim is to analyse the relation between Italian regions and the political behaviour of their communities: political discussions, participation in political meetings and marches, voluntary activity or donations to political parties and so on. The ranking is not correlated to voter turnout. We can assume that the politically engaged minority are unable to convince and involve the rest. At the same time, these small groups do not alter the general mistrust in parties and, generally speaking, in politics, which is spreading across Italy and also Europe.     

Finding disjoint paths on edge-colored graphs: more tractability results

The problem of finding the maximum number of vertex-disjoint uni-color paths in an edge-colored graph (called MaxCDP) has been recently introduced in literature, motivated by applications in social network analysis. In this paper we investigate how the complexity of the problem depends on graph parameters (namely the number of vertices to remove to make the graph a collection of disjoint paths and the size of the vertex cover of the graph), which makes sense since graphs in social networks are not random and have structure. The problem was known to be hard to approximate in polynomial time and not fixed-parameter tractable (FPT) for the natural parameter. Here, we show that it is still hard to approximate, even in FPT-time. Finally, we introduce a new variant of the problem, called MaxCDDP, whose goal is to find the maximum number of vertex-disjoint and color-disjoint uni-color paths. We extend some of the results of MaxCDP to this new variant, and we prove that unlike MaxCDP, MaxCDDP is already hard on graphs at distance two from disjoint paths.     

Themed section: the person-centred turn in welfare policies: bad wine in new bottles or a true social innovation?

This themed section is aimed at evaluating different personalised policies and at drawing a clear map of opportunities and challenges for future implementations. All the essays are based on evaluative researches and on original case studies. They concern different policies: the Australian National Disability Scheme (NDIS) a first serious venture into personalised funding; personalisation in the management of offenders in probation services within the English criminal justice system; social care services for young disabled people attempting to personalise their transition from childhood into adulthood (in Redbridge, UK); health personal plans for disabled people (in Sardinia, Italy). These case studies address the question of how transferable the concept of personalisation is from the social care sector to other and outline different methodologies for developing and evaluating person-centred policies. Last but not least they reflect on a bundle of issues which seem to emerge autonomously from such different case studies. We can sum up their results affirming that personalisation is not an individual consumer-client technology, simply confronted with a single market context and new professionals. It has to be steered within an appropriate context, including new type of professionals, users' led associations and a new governance's architecture. If the public role has to shape freedom and control, helping people to exercise choice in a collectively responsible way and, consequently, to participate in creating public goods, then the person-centred turn will have to confront, at least, some emergent issues, which in turn need specific forms of governance.