Factors influencing time to HIV disease progression in Romanian children

The purpose of this research was two-fold; to investigate the effect of institutionalization on death and CD4 decline in a cohort of 325 HIV-infected Romanian children, and to investigate the effect of disclosure of the child's own HIV status in this cohort. All children were treated with Kaletra-based highly active antiretroviral therapy, and were followed from November, 2001 through October, 2004. The mean age of the children included in the cohort is 13. The study found that children in biological families were more likely to experience disease progression through either death or CD4 decline than children in institutions (p=0.04). The family home-style institution may prove to be a replicable model for the safe and appropriate care of HIV-infected orphaned and abandoned children and teens. The study also found that children who do not know their own HIV infection status were more likely to experience disease progression through either death or CD4 decline than children who know their HIV diagnosis (p=0.03). This evidence suggests that, in the context of highly active anti retroviral therapy, knowledge of one's own HIV infection status is associated with delayed HIV disease progression. ^

Analyzing left-truncated right-censored data with uncertain onset time with parametric models

Prevalent sampling is an efficient and focused approach to the study of the natural history of disease. Right-censored time-to-event data observed from prospective prevalent cohort studies are often subject to left-truncated sampling. Left-truncated samples are not randomly selected from the population of interest and have a selection bias. Extensive studies have focused on estimating the unbiased distribution given left-truncated samples. However, in many applications, the exact date of disease onset was not observed. For example, in an HIV infection study, the exact HIV infection time is not observable. However, it is known that the HIV infection date occurred between two observable dates. Meeting these challenges motivated our study. We propose parametric models to estimate the unbiased distribution of left-truncated, right-censored time-to-event data with uncertain onset times. We first consider data from a length-biased sampling, a specific case in left-truncated samplings. Then we extend the proposed method to general left-truncated sampling. With a parametric model, we construct the full likelihood, given a biased sample with unobservable onset of disease. The parameters are estimated through the maximization of the constructed likelihood by adjusting the selection bias and unobservable exact onset. Simulations are conducted to evaluate the finite sample performance of the proposed methods. We apply the proposed method to an HIV infection study, estimating the unbiased survival function and covariance coefficients. ^

On the time to reach a critical number of infections in epidemic models with infective and susceptible immigrants.

In this paper we examine the time T to reach a critical number K0 of infections during an outbreak in an epidemic model with infective and susceptible immigrants. The underlying process X, which was first introduced by Ridler-Rowe (1967), is related to recurrent diseases and it appears to be analytically intractable. We present an approximating model inspired from the use of extreme values, and we derive formulae for the Laplace-Stieltjes transform of T and its moments, which are evaluated by using an iterative procedure. Numerical examples are presented to illustrate the effects of the contact and removal rates on the expected values of T and the threshold K0, when the initial time instant corresponds to an invasion time. We also study the exact reproduction number Rexact,0 and the population transmission number Rp, which are random versions of the basic reproduction number R0.

Parametric & nonparametric approaches to event studies: an application to a hotel’s market value

The main objective of this paper is twofold: on the one hand, to analyse the impact that the announcement of the opening of a new hotel has on the performance of its chain by carrying out an event study, and on the other hand, to compare the results of two different approaches to this method: a parametric specification based on the autoregressive conditional heteroskedasticity models to estimate the market model, and a nonparametric approach, which implies employing Theil’s nonparametric regression technique, which in turn, leads to the so-called complete nonparametric approach to event studies. The results that the empirical application arrives at are noteworthy as, on average, the reaction to such news releases is highly positive, both approaches reaching the same level of significance. However, a word of caution must be said when one is not only interested in detecting whether the market reacts, but also in obtaining an exhaustive calculation of the abnormal returns to further examine its determining factors.

The Boston Marathon and the Visa Negotiations between the EU and Russia: Time to get real and positive. CEPS Commentary, 8 May 2013

Against the background of the Boston Marathon bombing as a violent reminder of the lawlessness throughout much of the Northern Caucasus, Michael Emerson calls in this commentary for a fresh direction in the EU’s negotiations with Russia over visa-free travel. While finding that a ‘visa liberalisation’ regime has a very slim prospect of materialising any time soon, on the other hand, he sees realistic possibilities for fast delivery of a ‘virtual visa free regime’ of the multi-year, multi-entry visa, which would be a real and important achievement for EU-Russian relations.

Time to move north? CEPS Commentary, 27 May 2013

A staggering one out of every four young people is presently unemployed in Spain. And comparable numbers in Greece, Portugal and Italy are hardly more encouraging. Germany, on the other hand, enjoys a historically low youth unemployment rate of 8% and is experiencing skill shortages in some occupations. Against this background, this Commentary calls upon the European Commission to use its considerable strength and know-how in bringing partners and stakeholders together in order to facilitate the necessary infrastructure to allow better matching across borders of workers and employers. The authors point to the June European Council meeting as offering a good occasion to launch initiatives to this effect.

The EU and Syria – Time to Play behind Closed Doors. Jean Monnet/Robert Schuman Paper Series Special Issue, September 13, 2013

From the Introduction. Since the – presumed – utilization of chemical weapons against civilians by the Assad regime late August, the members of the Euro-Atlantic community have been building the case for a military intervention, a punishing mission against Bashar al-Assad. Despite evidences that sarin gas was used, the UK and Germany seem to be out of the race – for a similar reason: domestic politics –, leaving the US and France in the starting blocks. French President Hollande has expressed his commitment to go to war. The world is now on hold waiting for the US as President Obama, after asking US Congress to postpone a vote on a military intervention, is working on a possible diplomatic solution with Russian President Putin. Since Kerry’s comments in London earlier this week, Russian President Putin has been seeking for a diplomatic solution that would put all Syrian chemical arsenals under international supervision.