Luis C. Nunes

Mutations in CTC1, encoding conserved telomere maintenance component 1, cause Coats plus

Coats plus is a highly pleiotropic disorder particularly affecting the eye, brain, bone and gastrointestinal tract. Here, we show that Coats plus results from mutations in CTC1, encoding conserved telomere maintenance component 1, a member of the mammalian homolog of the yeast heterotrimeric CST telomeric capping complex. Consistent with the observation of shortened telomeres in an Arabidopsis CTC1 mutant and the phenotypic overlap of Coats plus with the telomeric maintenance disorders comprising dyskeratosis congenita, we observed shortened telomeres in three individuals with Coats plus and an increase in spontaneous γH2AX-positive cells in cell lines derived from two affected individuals. CTC1 is also a subunit of the α-accessory factor (AAF) complex, stimulating the activity of DNA polymerase-α primase, the only enzyme known to initiate DNA replication in eukaryotic cells. Thus, CTC1 may have a function in DNA metabolism that is necessary for but not specific to telomeric integrity.

Combining Averting Behavior and Contingent Valuation Data: An Application to Drinking Water Treatment

This paper is an empirical application that combines averting behavior with contingent valuation data. Consistency tests are performed incorporating alternative heteroscedastic structures in the bivariate probit models by taking advantage of the different information content that characterizes each data source. We look at three covariates not yet examined in the literature when combining stated and revealed preferred data to explain the variance in the models: income, the bid in the contingent valuation questionnaire, and the distance between the bid and the averting expenditures with drinking water. The models estimated include between and within data sources heteroscedasticity. The results obtained allow the combination of the two data sources under a common preference structure.

Protesting or Justifying? A Latent Class Model for Contingent Valuation with Attitudinal Data

This article develops a latent class model for estimating willingness-to-pay for public goods using simultaneously contingent valuation (CV) and attitudinal data capturing protest attitudes related to the lack of trust in public institutions providing those goods. A measure of the social cost associated with protest responses and the consequent loss in potential contributions for providing the public good is proposed. The presence of potential justification biases is further considered, that is, the possibility that for psychological reasons the response to the CV question affects the answers to the attitudinal questions. The results from our empirical application suggest that psychological factors should not be ignored in CV estimation for policy purposes, allowing for a correct identification of protest responses.

Spurious number of breaks

This paper considers the problem of choosing the number of breaks in the mean or trend of a series. We take the Schwarz-Bayesian criterion (SBC) which can be considered either as a proxy or as an alternative for what might be inferred from visual inspection of the graph of a time series. We show that spuriously many breaks will be inferred when the process is integrated of order one without breaks.

Instability in cointegration regressions: a brief review with an application to money demand in Portugal

This study addresses some modelling questions related to the possibility of structural change in models with nonstationary variables. Focusing on cointegration issues, some methodological aspects are discussed, attempting to integrate coherently the several steps of the modelling strategy. These range from unit root to cointegration testing and to testing for instability in the cointegration vector. An empirical example with Portuguese data tries to illustrate the usefulness of this approach, where a simple money demand function is estimated using an error-correction model (ECM). If a break is explicitly allowed in the cointegration vector the forecasting performance of the ECM improves.

The impact of pharmaceutical policy measures: An endogenous structural-break approach

Pharmaceutical spending in many countries has seen a steep increase in recent years. Governments have adopted several measures to reduce pharmaceutical expenditure growth, ranging from increased co-payments to price decreases determined administratively. Promotion of generic consumption has also ranked high in political priorities. We adopt a novel time series approach to the detection of which policy measures have a noticeable impact. The number and timing of the structural breaks are endogenously determined. As an illustration, we assess the overall impact of the several policy measures on total pharmaceutical spending, using monthly data from January 1995 to August 2008 for the Portuguese market. Our findings suggest that, in general, policy measures aimed at controlling pharmaceutical expenditure have been unsuccessful. Two breaks that were identified coincide with administratively determined price decreases. Measures aimed at increasing competition in the market had no visible effect on the dynamics of Government spending in pharmaceutical products. In particular, the introduction of reference pricing had only a transitory effect of less than one year, with historical growth resuming quickly. The consequence of this policy ineffectiveness is a transfer of financial burden from the Government to the patients, with no apparent effect on the dynamics of total pharmaceutical spending.

Identifying non-consistent choice behavior in recreation demand models

In a RPL model, rather than imposing consistency with consumer theory by constraining the distribution of the price coefficient to have negative support, a more general procedure is developed. Non-consistent choice behavior is identified in a recreation demand model for game reserves in South Africa.

Tests for Multiple Breaks in the Trend with Stationary or Integrated Shocks

In this paper, we propose new tests of the presence of multiple breaks in the trend of a univariate time-series where the number and dates of the breaks are unknown and that are valid in the presence of stationary or unit root shocks. These tests can also be used to sequentially estimate the number of breaks. The behaviour of the proposed tests is studied through Monte Carlo experiments.

Insights into the Responsiveness of Cork Oak (Quercus suber L.) to Bark Harvesting

Insights into the Responsiveness of Cork Oak ( Quercus suber L.) to Bark HarvestingThe cork oak (Quercus suber L.) is harvested for its bark (cork), a highly valuable non-timber forest product. Recurrent cork harvesting is practiced over the lifetime of the tree and constitutes a stressful action that, while artificially promoting cork growth, may severely deplete tree vigor after an exploitation time span. To date, few long-term studies have been conducted regarding the effect of recurrent cork harvests on cork growth rates, and there is a complete lack of knowledge on the effect of the stress, induced by cork harvesting, on the vigor of the cork oak. In this study we propose to address the resilience of the cork oak to cork harvesting, using cork-ring width as an indicator of tree vigor. We use dendrochronological methods to develop an extended cork-ring width series that was analyzed by autoregressive integrated moving average modeling with an intervention analysis approach. We show that cork harvesting represents a human-induced loss of tree resilience only after six consecutive harvests, and that only after a single stochastic cork-harvesting event may trigger a sudden collapse in cork oak vigor. Our results also suggest that the tree (optimum) exploitation period of 110–120 years, which includes more than nine consecutive harvests, extends more than 35 years beyond the tree vigor breakpoint (occurring at the sixth consecutive harvest). Within this time frame, the tree is producing cork instinctively to survive, and its vulnerability to other (a)biotic stresses may increase, leading to untimely cork oak decline. These results suggest that there is a great potential in the time-series analysis of cork-ring widths for the development of tools that may enhance typical cork oak management planning by addressing both economic and ecological objectives.Compreender a capacidade de resposta do sobreiro ( Quercus suber L.) ao descortiçamentoO sobreiro (Quercus suber L.) distingue-se das outras árvores pelas características singulares da sua espessa casca suberosa, a cortiça. Atualmente, a cortiça é considerada um importante produto não-lenhoso da floresta da região Mediterrânica, com elevado valor comercial. A extração da cortiça (descortiçamento) é feita periodicamente ao longo da vida da árvore, em sucessivos ciclos de produção de cortiça. Após um descortiçamento, a camada geradora de cortiça (felogene) morre e a árvore tem a capacidade de regenerar uma nova que, quase imediatamente, começa a formar novas camadas de cortiça. A longo prazo, os sucessivos descortiçamentos, do mesmo modo que “forçam” a árvore a produzir novas camadas de cortiça, afetam decisivamente os processos fisiológicos da árvore. Apesar de bem estudadas, as reações fisiológicas imediatas do sobreiro ao descortiçamento e a curva crescimento de cortiça num ciclo de produção, nada se sabe sobre como a árvore reage a sucessivos descortiçamentos, ao longo da sua vida.Neste estudo, apresenta-se uma abordagem inovadora para obter informação sobre a variação da resiliência do sobreiro ao descortiçamento. Assume-se que a largura do anel de crescimento da cortiça é um indicador do vigor vegetativo da árvore e efetuou-se uma análise dendrocronológica de séries temporais extensas da largura dos anéis para modelar o crescimento da cortiça. Os resultados obtidos mostraram que a resposta da árvore ao descortiçamento é diferente ao longo da sua vida. A partir de determinado descortiçamento, a árvore tem um colapso da sua resiliência ao descortiçamento, reduzindo drasticamente a largura do seu anel de crescimento da cortiça. A explorabilidade económica da árvore estende-se muito para além deste colapso na sua resiliência ao descortiçamento, a partir do qual poderá aumentar a vulnerabilidade da árvore a outros agentes nocivos (a)bióticos e a promover a sua morte prematura.

Consistency in Mixed Demand Systems: Contingent Valuation and Travel Cost Data

In contrast to previous literature, we propose a consistency test that does not impose any particular common functional form for the preference structure underlying the travel cost (TC) and contingent valuation (CV) models. We derive testable consistency conditions between TC and CV data in the context of mixed demand systems when valuing changes in environmental quality. These conditions are a subset of the rationality conditions. The proposed consistency tests are implemented combining TC and CV data. The empirical results show that it is possible to combine stated TC and CV, but not revealed TC and CV data.