A likelihood-based constrained algorithm for multivariate normal mixture models

It is well known that the log-likelihood function for samples coming from normal mixture distributions may present spurious maxima and singularities. For this reason here we reformulate some Hathaways results and we propose two constrained estimation procedures for multivariate normal mixture modelling according to the likelihood approach. Their perfomances are illustrated on the grounds of some numerical simulations based on the EM algorithm. A comparison between multivariate normal mixtures and the hot-deck approach in missing data imputation is also considered.Salvatore Ingrassia: S. Ingrassia carried out the research as part of the project Metodi Statistici e Reti Neuronali per lAnalisi di Dati Complessi (PRIN 2000, resp. G. Lunetta).     

Entrepreneurial Orientation in low- and medium-tech industries: The need for Absorptive Capacity to increase performance

The implications of Entrepreneurial Orientation (EO) for firm performance in low- and medium-tech (LMT) industries are largely unexplored and seem to be limited. In this paper we seek to address this research gap studying how Absorptive Capacity can act as a key factor determining the effectiveness of EO in such a context. Specifically, we adopt the knowledge-based view of the firm and explore the moderating effects of Absorptive Capacity’s Potential and Realized dimensions on the EO–performance relationship in LMT industries. Our regression results based on a lagged dataset of 103 medium-sized firms based in Italy confirm our hypotheses that, in LMT industries, EO has a positive effect on firm performance when coupled with high levels of both Potential and Realized Absorptive Capacity.     

The effect of natural disasters on nuptiality: evidence from L’Aquila earthquake (Italy)

Population and Environment - Drawing on socio-psychology and economics literature contributions, this paper provides an original conceptual framework examining whether and how natural disasters...     

Stay at Home! Governance Quality and Effectiveness of Lockdown

Social Indicators Research - In order to control the spread of the COVID-19 pandemic, during the first wave of the pandemic numerous countries decided to adopt lockdown policies. It had been a...     

Determinants of Foreign Workers’ Wages in Two Italian Regions with High Illegal Immigration

Since the end of the 1970s Italy has moved from being an out-migration country to being a foreign immigration country, but very few studies have addressed the factors determining the wages of immigrant workers, owing to the lack of available data. In this paper we analyse the determinants of the wages of immigrants in some areas of Latium and Campania, where the share of illegal immigration is relatively high, using the results of a set of sample surveys which collected information on several aspects of the immigration process in the years 1993–94. The purpose of the article is to shed some light on the factors underlying wage distribution among the immigrants using an estimation method that controls for sample selection problems. According to the empirical results, income differences seem to be relatively high among immigrants. Differences in labour market integration among sexes and area of origin clearly emerge from the results. Moreover, legal status plays an important role in the explanation of the wage gap between documented and undocumented immigrants, also because of the different occupational sector structure in the two groups.