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Surrogate models are frequently used to replace costly engineering simulations. A single surrogate is frequently chosen based on previous experience or by fitting multiple surrogates and selecting one based on mean cross-validation errors. A novel stacking strategy will be presented in this paper. This new strategy results from reinterpreting the model selection process based on the generalization error. For the first time, this problem is proposed to be translated into a well-studied financial problem: portfolio management and optimization. In short, it is demonstrated that the individual residues calculated by leave-one-out procedures are samples from a given random variable ϵi, whose second non-central moment is the i-th model's generalization error. Thus, a stacking methodology based solely on evaluating the behavior of the linear combination of the random variables ϵi is proposed. At first, several surrogate models are calibrated. The Directed Bubble Hierarchical Tree (DBHT) clustering algorithm is then used to determine which models are worth stacking. The stacking weights can be calculated using any financial approach to the portfolio optimization problem. This alternative understanding of the problem enables practitioners to use established financial methodologies to calculate the models' weights, significantly improving the ensemble of models' out-of-sample performance. A study case is carried out to demonstrate the applicability of the new methodology. Overall, a total of 124 models were trained using a specific dataset: 40 Machine Learning models and 84 Polynomial Chaos Expansion models (which considered 3 types of base random variables, 7 least square algorithms for fitting the up to fourth order expansion's coefficients). Among those, 99 models could be fitted without convergence and other numerical issues. The DBHT algorithm with Pearson correlation distance and generalization error similarity was able to select a subgroup of 23 models from the 99 fitted ones, implying a reduction of about 77% in the total number of models, representing a good filtering scheme which still preserves diversity. Finally, it has been demonstrated that the weights obtained by building a Hierarchical Risk Parity (HPR) portfolio perform better for various input random variables, indicating better out-of-sample performance. In this way, an economic stacking strategy has demonstrated its worth in improving the out-of-sample capabilities of stacked models, which illustrates how the new understanding of model stacking methodologies may be useful.

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INTRODUCTION: Gout occurs frequently in patients with kidney disease and can lead to a significant burden on quality of life. Gout prevalence, and its association with outcomes in hemodialysis (HD) and peritoneal dialysis (PD) populations located in North America, is unknown. METHODS: We used data from North America cohorts of 70,297 HD patients (DOPPS, 2012-2020) and 5117 PD patients (PDOPPS, 2014-2020). We used three definitions of gout for this analysis: (1) having an active prescription for colchicine or febuxostat; (2) having an active prescription for colchicine, febuxostat, or allopurinol; or (3) having an active prescription for colchicine, febuxostat, or allopurinol, or prior diagnosis of gout. Propensity score matching was used to compare outcomes among patients with versus without gout. Outcomes included erythropoietin resistance index (ERI=erythropoiesis stimulating agent dose per week/(hemoglobin×weight)), all-cause mortality, hospitalization, and patient-reported outcomes (PROs). RESULTS: The gout prevalence was 13% in HD and 21% in PD; it was highest among incident dialysis patients. Description of previous history of gout was rare, and identification of gout defined by colchicine (2%-3%) or febuxostat (1%) prescription was less frequent than by allopurinol (9%-12%). Both HD and PD patients with gout (versus no gout) were older, were more likely male, had higher body mass index, and had higher prevalence of cardiovascular comorbidities. About half of patients with a gout history were prescribed urate-lowering therapy. After propensity score matching, mean ERI was 3%-6% higher for gout versus non-gout patients while there was minimal evidence of association with clinical outcomes or PROs. CONCLUSION: In a large cohort of PD and HD patients in North America, we found that gout occurs frequently and is likely under-reported. Gout was not associated with adverse clinical or PROs.

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Introduction: Since most of the autoimmune diseases (AID) affect mostly women in their fertile years, and fertility is in general preserved, the use of disease-modifying antirheumatic drugs (DMARDs) during conception, pregnancy, and lactation has been a matter of concern in the treatment of women affected by AID. Areas covered: We performed a comprehensive review of the latest and most relevant research papers published in the field and discussed different aspects related to the use of synthetic and biologic DMARDs and immunosuppressants in the preconceptional period, during pregnancy and lactation in AID patients, both in males and females. Expert commentary: Active AID impose an increased risk for adverse maternal and fetal outcomes, such as preeclampsia, miscarriage, intrauterine growth restriction, prematurity, low birth weight, and stillbirth. Family planning with proper contraception and shared decision-making on the ideal time to conceive with treatment adjustment must be a rule. One of the main challenges when counseling and/or adjusting treatment of patients that are planning a pregnancy is to provide a medication that is at the same time efficacious and safe at the conceptional period and to developing the fetus.

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The current treatment for antiphospholipid syndrome (APS) with thrombotic manifestation is long-term anticoagulation. Vitamin K antagonists (VKA) are usually the agents of choice. However, VKA limitations, such as unpredictable anticoagulation effects due to interaction with diet and other drugs, require regular monitoring. This may impact on patients' quality of life. Since the approval of new oral anticoagulants (NOAC) for non-valvular atrial fibrillation and deep vein thrombosis prevention, much has been speculated about its use in APS patients. We report here a series of eight APS patients with failure of thrombotic prevention during rivaroxaban use. All patients had venous thrombosis as the initial manifestation of APS, and two of them also had arterial manifestations. Three patients had triple antibody positivity. Five patients developed arterial events during the treatment with rivaroxaban. Until the results of ongoing trials of rivaroxaban for APS are presented, NOAC should not be recommended to APS patients. Our preliminary experience as well cases previously reported in the literature suggest that there is a high-risk group that is less protected with rivaroxaban, namely those with previous arterial thrombosis or triple positivity. VKA remains to be the mainstay treatment for thrombotic APS.

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Respiratory tract disorders in the juvenile rheumatic diseases are not infrequent and can have different clinical features when compared with those in the adult diseases. The purpose of this review article is to show the main manifestations of the respiratory tract, with an emphasis on lung involvement, in the most frequent juvenile rheumatic diseases.

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Distúrbios do aparelho respiratório nas doenças reumáticas que acometem a faixa etária pediátrica não são raros e podem apresentar características clínicas diferentes quando comparados ao quadro clínico de adultos. Este artigo de revisão procura mostrar as principais manifestações do aparelho respiratório, com ênfase no acometimento pulmonar, nas principais doenças reumáticas da infância e adolescência.

Respiratory tract disorders in the juvenile rheumatic diseases are not infrequent and can have different clinical features when compared with those in the adult diseases. The purpose of this review article is to show the main manifestations of the respiratory tract, with an emphasis on lung involvement, in the most frequent juvenile rheumatic diseases.

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