Francisco Montes

Pegylated α-interferon-2a plus ribavirin compared with pegylated α-interferon-2b plus ribavirin for initial treatment of chronic hepatitis C virus: Prospective, non-randomized study

Background and Aim:  We assessed whether the two regimens of pegylated α‐interferon‐2b (PEG‐IFN‐α2b) plus ribavirin and pegylated α‐interferon‐2a (PEG‐IFN‐α2a) plus ribavirin showed differences in terms of sustained virological response, withdrawal due to side‐effects and dose adjustment requirements in the treatment of naive chronic hepatitis C virus (HCV) patients.

Modelling and forecasting mortality in Spain

Experience shows that static life tables overestimate death probabilities. As a consequence of this overestimation the premiums for annuities, pensions and life insurance are not what they actually should be, with negative effects for insurance companies or policy-holders. The reason for this overestimation is that static life tables, through being computed for a specific period of time, cannot take into account the decreasing mortality trend over time. Dynamic life tables overcome this problem by incorporating the influence of the calendar when graduating mortality. Recent papers on the topic look for the development of new methods to deal with this dynamism. Most methods used in dynamic tables are parametric, apply traditional mortality laws and then analyse the evolution of estimated parameters with time series techniques. Our contribution consists in extending and applying Lee-Carter methods to Spanish mortality data, exploring residuals and future trends.

Model comparison and selection for stationary space-time models

An intensive simulation study to compare the spatio-temporal prediction performances among various space-time models is presented. The models having separable spatio-temporal covariance functions and nonseparable ones, under various scenarios, are also considered. The computational performance among the various selected models are compared. The issue of how to select an appropriate space-time model by accounting for the tradeoff between goodness-of-fit and model complexity is addressed. Performances of the two commonly used model-selection criteria, Akaike information criterion and Bayesian information criterion are examined. Furthermore, a practical application based on the statistical analysis of surface shortwave radiation budget (SSRB) data is presented.

Modelling residuals dependence in dynamic life tables: A geostatistical approach

The problem of modelling dynamic mortality tables is considered. In this context, the influence of age on data graduation needs to be properly assessed through a dynamic model, as mortality progresses over the years. After detrending the raw data, the residuals dependence structure is analysed, by considering them as a realisation of a homogeneous Gaussian random field defined on RxR. This setting allows for the implementation of geostatistical techniques for the estimation of the dependence and further interpolation in the domain of interest. In particular, a complex form of interaction between age and time is considered, by taking into account a zonally anisotropic component embedded into a nonseparable covariance structure. The estimated structure is then used for prediction of mortality rates, and goodness-of-fit testing is performed through some cross-validation techniques. Comments on validity and interpretation of the results are given.

The lack of balance in the Spanish First Division football league

Research question: The importance of balance in sports competitions has been made evident on many occasions. The dominance of a few teams over the rest of the participants in the Spanish First Division Football League has made the subject of a lack of balance an omnipresent one in sports journalism. The aim of this article is to show that the lack of balance is not just a matter of the past few seasons, but also it has been evidenced since far back in time. To test this hypothesis, the results of the league have been analyzed since its inception through various static and dynamic indices of competitive balance. Research methods: The empirical distribution of static and dynamic indices under the hypothesis of perfect balance were obtained by means of a simulation procedure. A Montecarlo test is used to contrast the hypothesis of balance in each season. The performance of this test is also evaluated. Results and findings: Both the static and the dynamic analyses confirm the competitive imbalance in the First Division league practically since its beginnings, with the occasional exception which does not invalidate this statement. Implications: The imbalance influences the low attendance at the stadiums. The Spanish league managers must contrive some measures to reduce this imbalance. The first of them should be a fairer distribution of TV rights since with the current system the ratio between the highest and lowest receivers is 12 to 1 while in the other European leagues it does not exceed 2 to 1.

Pseudo-likelihood Inference for Gibbs Processes with Exponential Families through Generalized Linear Models

Parameter estimation for two-dimensional point pattern data is difficult, because most of the available stochastic models have intractable likelihoods which usually depend on an unknown scaling factor. However, this problem can be bypassed using the pseudo-likelihood estimation method. Baddeley and Turner (1998) presented a numerical algorithm for computing approximated maximum pseudo-likelihood estimates for Gibbs point processes with exponential family likelihoods. We use their method and a new technique based on Voronoi polygons to evaluate the qua-drature points to present an intensive comparative simulation study which evaluates the performance of these two methods compared to the traditional approximation under varying circumstances. Two Gibbs point process models, the Strauss and saturation processes, have been used.

Temporal Evolution of Mortality Indicators

Abstract In Spain, as in other developed countries, significant changes in mortality patterns have occurred during the 20th and 21st centuries. One reflection of these changes is life expectancy, which has improved in this period, although the robustness of this indicator prevents these changes from being of the same order as those for the probability of death. If, moreover, we bear in mind that life expectancy offers no information as to whether this improvement is the same for different age groups, it is important and necessary to turn to other mortality indicators whose past and future evolution in Spain we are going to study. These indicators are applied to Spanish mortality data for the period 1981–2008, for the age range 0–99. To study its future evolution, the mortality ratios have to be projected using an adequate methodology, namely, the Lee-Carter model. Confidence intervals for these predictions can be calculated using the methodology that Lee and Carter apply in their original article for expected lifetime confidence intervals, but they take into account only the error in the prediction of the mortality index obtained from the ARIMA model adjusted to its temporal series, excluding other sources of error such as that introduced by estimations of the other parameters in the model. That is why bootstrap procedures are preferred, permitting the combination of all sources of uncertainty.

Measuring spatial inhomogeneity at different spatial scales using hybrids of Gibbs point process models

Infectious diseases give rise to complex spatial patterns exhibiting aggregation at different scales. Baddeley (J Stat Softw 55:1–43, 2013) proposed a technique for constructing new Gibbs models for spatial point patterns, combining existing models available in the literature. We use their proposal to model the spatial point pattern of varicella, a highly contagious airborne disease, in Valencia, Spain. We employed descriptive analysis to get a glimpse of the basic properties of the point pattern. Covariate information such as the density of population (children under 14 years old) living in the study region, the distance to the nearest school, and the composition of families (expressed as the average number of persons per family) is used to describe the intensity of the process. We used SatScan to identify main clusters of schools, and to feed the model with this further information. Our analysis shows the relation between varicella cases and school locations, and highlights aggregation in the data at different spatial scales.

Low intensity magnetic field influences short-term memory: A study in a group of healthy students.

This study analyzes if an external magnetic stimulus (2 kHz and approximately 0.1 μT applied near frontal cortex) influences working memory, perception, binary decision, motor execution, and sustained attention in humans. A magnetic stimulus and a sham stimulus were applied to both sides of the head (frontal cortex close to temporal-parietal area) in young and healthy male test subjects (n = 65) while performing Sternbergs memory scanning task. There was a significant change in reaction time. Times recorded for perception, sustained attention, and motor execution were lower in exposed subjects (P < 0.01). However, time employed in binary decision increased for subjects exposed to magnetic fields. From results, it seems that a low intensity 2 kHz exposure modifies short-term working memory, as well as perception, binary decision, motor execution, and sustained attention.

Space-time airborne disease mapping applied to detect specific behaviour of varicella in Valencia, Spain.

Airborne diseases are one of humanitys most feared sicknesses and have regularly caused concern among specialists. Varicella is an airborne disease which usually affects children before the age of 10. Because of its nature, varicella gives rise to interesting spatial, temporal and spatio-temporal patterns. This paper studies spatio-temporal exploratory analysis tools to detect specific behaviour of varicella in the city of Valencia, Spain, from 2008 to 2013. These methods have shown a significant association between the spatial and the temporal component, confirmed by the space-time models applied to the data. High relative risk of varicella is observed in economically disadvantaged regions, areas less involved in vaccination programmes.