Log-ratio methods in mixture models for compositional data sets

When traditional methods are applied to compositional data misleading and incoherent results could be obtained. Finite mixtures of multivariate distributions are becoming increasingly important nowadays. In this paper, traditional strategies to fit a mixture model into compositional data sets are revisited and the major difficulties are detailed. A new proposal using a mixture of distributions defined on orthonormal log-ratio coordinates is introduced. A real data set analysis is presented to illustrate and compare the different methodologies

Compositional random data: a routine for CoDaPack

Generation of random variables are needed in the simulations of many natural process. For some random variables, di erent methodologies are known, specially into euclidean spaces. In this paper a routine for dealing with random variables into a simplex space with the Aitchison geometry is presented. The routine has been implemented for the CoDaPack, a freeware software developed to be used for users with minimum programming skills

Statins and new-onset atrial fibrillation in a cohort of patients with hypertension: analysis of electronic health records, 2006-2015

Atrial Fibrillation; Electronic Health Records; HypertensionFibrilación atrial; Registros Electrónicos de Salud; HipertensiónFibril·lació atrial ; Registres Electrònics de Salut; HipertensióHypertension is the most prevalent risk factor for new-onset atrial fibrillation (AF). But few studies have addressed the effect of statins on the incidence of this arrhythmia in patients with hypertension. This study aimed to evaluate the effect of statins on new-onset of this arrhythmia in a hypertensive population, accounting for AF risk. Data from the Information System for the Development of Research in Primary Care was used to recruit a retrospective cohort of ≥55-year-old hypertensive individuals with no ischemic vascular disease, in 2006-2007, followed up through 2015. The effect of initiating statin treatment on new-onset atrial fibrillation was assessed with Cox proportional hazards models adjusted by the propensity score of receiving statin treatment, in the overall study population and stratified by AF risk. Of 100 276 included participants, 9814 initiated statin treatment. The AF incidence per 1000 person-years (95% confidence interval) was 12.5 (12.3-12.8). Statin use associated with a significant (9%) reduction in AF incidence. Differences in absolute AF incidence were higher in the highest AF risk subgroup, and the estimated number needed to treat to avoid one case was 720. The relative effect was poor, similar across groups, and non-significant, as was the association of statins with adverse effects. We found a limited protective effect of statins over new-onset AF in this hypertensive population with no ischemic vascular disease. If there is no further indication, hypertensive patients would not benefit from statin use solely for AF primary prevention

Individuals With SARS-CoV-2 Infection During the First and Second Waves in Catalonia, Spain: Retrospective Observational Study Using Daily Updated Data

Coronavirus SARS-CoV-2; COVID-19; 2019-nCoV; Epidemiologia; ComparacióCoronavirus SARS-CoV-2; COVID-19; 2019-nCoV; Epidemiología; ComparaciónCoronavirus SARS-CoV-2; COVID-19; 2019-nCoV; Epidemiology; ComparisonA description of individuals with SARS-CoV-2 infection comparing the first and second waves could help adapt health services to manage this highly transmissible infection.Objective: We aimed to describe the epidemiology of individuals with suspected SARS-CoV-2 infection, and the characteristics of patients with a positive test comparing the first and second waves in Catalonia, Spain. Methods: This study had 2 stages. First, we analyzed daily updated data on SARS-CoV-2 infection in individuals from Girona (Catalonia). Second, we compared 2 retrospective cohorts of patients with a positive reverse-transcription polymerase chain reaction or rapid antigen test for SARS-CoV-2. The severity of patients with a positive test was defined by their admission to hospital, admission to intermediate respiratory care, admission to the intensive care unit, or death. The first wave was from March 1, 2020, to June 24, 2020, and the second wave was from June 25, 2020, to December 8, 2020.Results: The numbers of tests and cases were lower in the first wave than in the second wave (26,096 tests and 3140 cases in the first wave versus 140,332 tests and 11,800 cases in the second wave), but the percentage of positive results was higher in the first wave than in the second wave (12.0% versus 8.4%). Among individuals with a positive diagnostic test, 818 needed hospitalization in the first wave and 680 in the second; however, the percentage of hospitalized individuals was higher in the first wave than in the second wave (26.1% versus 5.8%). The group that was not admitted to hospital included older people and those with a higher percentage of comorbidities in the first wave, whereas the characteristics of the groups admitted to hospital were more alike.This work was supported by grants from the European Union ERDF funds (Network for Prevention and Health Promotion in Primary Care, RedIAPP–CARDIOCAT; RD16/0007/0004) and from the Agency for Management of University and Research Grants (AGAUR; 2017-SGR 1146). We thank Eric Tornabell for his technical support. We also thank all health care professionals for their ceaseless work to care for COVID-19 patients in this pandemic

Enhancing the First-Pass Effect in Acute Stroke: The Impact of Stent Retriever Characteristics

Introduction: Although stentrievers (SRs) have been a mainstay of mechanical thrombectomy (MT), and current guidelines recommend the use of SRs in the treatment of large vessel occlusion stroke (LVO), there is a paucity of studies in the literature comparing SRs directly against each other in terms of mechanical and functional properties. Timely access to endovascular therapy and the ability to restore intracranial flow in a safe, efficient, and efficacious manner have been critical to the success of MT. This study aimed to investigate the impact of contemporary SR characteristics, including model, brand, size, and length, on the first-pass effect (FPE) in patients with acute ischemic stroke. Methods: Consecutive patients with M1 occlusion treated with a single SR+BGC were recruited from the ROSSETTI registry. The primary outcome was the FPE that was defined as modified (mFPE) or true (tFPE) for the achievement of modified thrombolysis in cerebral infarction (mTICI) grades 2b-3 or 3 after a single device pass, respectively. We compared patients who achieved mFPE with those who achieved tFPE according to SR characteristics. Results: We included 610 patients (52.3% female and 47.7% male, mean age 75.1 +/- 13.62 years). mFPE was achieved in 357 patients (58.5%), whereas tFPE was achieved in 264 (43.3%). There was no significant association between SR characteristics and mFPE or tFPE. Specifically, the SR size did not show a statistically significant relationship with improvement in FPE. Similarly, the length of the SR did not yield significant differences in the mFPE and tFPE, even when the data were grouped. Conclusions: Our data indicate that contemporary SR-mediated thrombectomy characteristics, including model, brand, size, and length, do not significantly affect the FPE

Aportacions de l'anàlisi composicional a les mixtures de distribucions

The present thesis is a compendium of three original works produced between 2014 and 2018. The papers have a common link: they are different contributions made by compositional data analysis to the study of the models based on mixtures of probability distributions. In brief, we could say that compositional data analysis is a methodology that consists of studying a sample of measures that are strictly positive from a relative point of view. Mixtures of distributions are a specific type of probability distribution defined to be the convex linear combination of other distributionsLa present tesi representa un compendi de tres treballs originals realitzats durant els anys 2014-2018. Aquests treballs comparteixen un nexe comú: tots ells són diferents aportacions de l'anàlisi composicional a l'estudi dels models basats en mixtures de distribucions de probabilitat. D'una forma molt breu, podríem dir que l'anàlisi composicional és una metodologia consistent en estudiar una mostra de mesures estrictament positives des d'un punt de vista relatiu. Les mixtures de distribucions, també anomenades barreges de distribucions, són un tipus particular de distribucions de probabilitat definides com la combinació lineal convexa d'altres distribucion

Vertex fusion under diameter constraints

Given a graph $G$=($V$,$E$), a positive integer $k$ and a positive integer $d$, we want find a subset $V_k$ with $k$ vertices such the graph obtained by identifying the vertices from $V_k$ in $G$ has diameter at most $d$. We prove that for every $d geq 2$ the problem is NP-complete. For the case of trees we provide a polynomial time algorithm that exploits the relationship with the $r$-dominating set problem

Vertex fusion under diameter constraints

Given a graph $G$=($V$,$E$), a positive integer $k$ and a positive integer $d$, we want find a subset $V_k$ with $k$ vertices such the graph obtained by identifying the vertices from $V_k$ in $G$ has diameter at most $d$. We prove that for every $d geq 2$ the problem is NP-complete. For the case of trees we provide a polynomial time algorithm that exploits the relationship with the $r$-dominating set problem.Postprint (published version

Vertex fusion under diameter constraints

Given a graph $G$=($V$,$E$), a positive integer $k$ and a positive integer $d$, we want find a subset $V_k$ with $k$ vertices such the graph obtained by identifying the vertices from $V_k$ in $G$ has diameter at most $d$. We prove that for every $d geq 2$ the problem is NP-complete. For the case of trees we provide a polynomial time algorithm that exploits the relationship with the $r$-dominating set problem