When do improved covariance matrix estimators enhance portfolio optimization? An empirical comparative study of nine estimators

The use of improved covariance matrix estimators as an alternative to the sample estimator is considered an important approach for enhancing portfolio optimization. Here we empirically compare the performance of nine improved covariance estimation procedures using daily returns of 90 highly capitalized US stocks for the period 1997–2007. We find that the usefulness of covariance matrix estimators strongly depends on the ratio between the estimation period T and the number of stocks N, on the presence or absence of short selling, and on the performance metric considered. When short selling is allowed, several estimation methods achieve a realized risk that is significantly smaller than that obtained with the sample covariance method. This is particularly true when T/N is close to one. Moreover, many estimators reduce the fraction of negative portfolio weights, while little improvement is achieved in the degree of diversification. On the contrary, when short selling is not allowed and T?>?N, the considered methods are unable to outperform the sample covariance in terms of realized risk, but can give much more diversified portfolios than that obtained with the sample covariance. When T?<?N, the use of the sample covariance matrix and of the pseudo-inverse gives portfolios with very poor performance.     

Social Media managerial implications for budget accommodation venues: use of Social Media platforms more effectively and efficiently

Quality & Quantity - Social Media has transformed people’s lives and behaviour. Over the past decade it has also transformed the Tourism Industry. Despite this triumph, insufficient...     

Type of diversification and firm resources: new empirical evidence from the Spanish tourism industry

This paper analyses the diversification strategies followed by tourism firms from the perspective of the resource‐based view. More specifically, it seeks to verify whether the composition of the firms' resources has a bearing on the decision to undertake one type of diversification or another (related or unrelated). From a mail survey to 80 Spanish tourism firms, we identified 94 entries into new business areas. We applied an ordered logit regression and have statistically confirmed that intangible resources lead to a more related type of diversification. Copyright © 2008 John Wiley & Sons, Ltd.     

An empirical investigation of the sustainability of the public deficit in Portugal

In this paper, we investigate Portuguese government expenditures and revenues as an example for a long time series. Our hypothesis states that there may be periods when the deficit is sustainable and those when it is not. Usually, after a period of unsustainable deficits, a new regime takes over. These regime shifts call for an approach that takes into account a non-constant structure of the underlying data generating process. Consequently, we use different tests which we set up in a time-varying framework. We apply and compare the results of the Trace test, Breitung’s non-parametric test and the Bohn test. We identify several break points and find that the Trace test performs worst in this case while Breitung’s test and the Bohn test give similar results. Comparing the results with history, we find that the last two tests best reflect what happened historically.     

Network analysis approach to map tourism mobility

The spatial distribution of tourists is uneven and it can include some areas at regional and/or sub-regional level. The social–economic and environmental impacts of tourism, are concentrated in different areas. Some recent contributions show the usefulness and the effectiveness of network analysis (NA) approach in revising the organization of tourist facilities and services. This paper proposes to apply methods borrowed from NA to map the spatial distribution of tourism mobility in Sicily. So, we analyze the network features of tourism in a multi-destinations net. By means of traditional measures of NA, we propose to measure the links among destinations. The study aims to connect destinations, represented as nodes, to define a territorial network of tourism demand. In the specific instance, the degree centrality, closeness centrality, betweenness centrality are used to localize central areas and the main routes. We test survey data collected on a sample of tourists leaving from airports and ports of the main Sicilian cities, who visited two destinations at least. Then, we study tourism mobility on those areas selected by tourists. Finally, employing measures derived from NA, the work attempts to set out territorial networks. This approach could be useful to plane tourism development policies.     

Internationalisation speed and technological patterns: A panel data study on Spanish SMEs

The last ten years has seen a proliferation of works attempting to explain why some firms internationalise rapidly, rather than following a sequential process. Many of these works have focused on the role of technology as the driving force behind the phenomenon. Following this argument, this work studies the effect that different technological patterns have on firms' internationalisation speed. In order to observe this effect, a sample of 945 SMEs was used over a 17-year period (1990–2006). By undertaking a micro-level analysis, we explain the possible effect of sectoral technological intensity on internationalisation speed, observing significant differences between technology-intensive and non-intensive sectors, and identify which technological parameters have a greater effect on the acceleration of internationalisation in each of these sectors.     

Imported inputs and skill upgrading

This paper studies the effect of imported inputs on the relative demand for high-skill labor. To this purpose, it applies propensity score matching techniques to firm-level data for 27 transition countries. The results show that importing inputs induces skill upgrading. Specifically, it explains more than one-quarter of the unconditional difference between importers and non-importers in the employment share of high-skill workers. The paper explores possible mechanisms behind this result. In particular, it reports suggestive evidence that importing leads firms to engage in high-skill intensive activities, such as production of new goods, improvement of product quality and, to a lesser extent, R&D and technology adoption.     

The effects of public infrastructure on the cost structure of Spanish industries

This paper examines the impact of public infrastructures on the performance of Spanish private business at a disaggregated industry level. We use duality theory to recover the productivity effects of public capital by calculating the cost saving effects that are associated to public services. Using a translog cost function we present panel estimates for 14 Spanish industries during the period 1980–1991. Our results strongly suggest that public capital formation can be considered to be an instrument to improve competitiveness by reducing production costs. However, the results also indicate that there is a technologically induced labor saving effect through higher public investment. Furthermore, our estimates suggest that a distinction among industries is of importance because the effects of public infrastructures vary across industries considerably.     

Addendum: Gender discrimination and intergenerational transmission of preferences

The paper ‘Gender discrimination and intergenerationaltransmission of preferences’ was published in Oxford