1,721,091 research outputs found
Interval-Wise Control of the Family Wise Error Rate: a New Inferential Procedure in Functional Data Analysis
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Modelling time‐varying mobility flows using function‐on‐function regression: analysis of a bike sharing system in the city of Milan
No full textIn today's world, bike sharing systems are becoming in- creasingly common in all main cities around the world. To understand the spatiotemporal patterns of how people move by bike through the city of Milan, we apply func- tional data analysis to study the flows of a bike sharing mobility network. We introduce a complete pipeline to properly analyse and model functional data through a con- current functional-on-functional model taking into account the effects of weather conditions and calendar on the bike flows. In the end, we develop an interactive interface to explore the results of the analyses
Testing Phase and Amplitude Variability in Functional Data Analysis: a Hierarchical Permutation Test Approach
No full textThe interval testing procedure: a general framework for inference in functional data analysis
No full textWe introduce in this work the Interval Testing Procedure (ITP), a novel inferential technique for functional data. The procedure can be used to test different functional hypotheses, e.g., distributional equality between two or more functional populations, equality of mean function of a functional population to a reference. ITP involves three steps: (i) the representation of data on a (possibly high-dimensional) functional basis; (ii) the test of each possible set of consecutive basis coefficients; (iii) the computation of the adjusted p-values associated to each basis component, by means of a new strategy here proposed. We define a new type of error control, the interval-wise control of the family wise error rate, particularly suited for functional data. We show that ITP is provided with such a control. A simulation study comparing ITP with other testing procedures is reported. ITP is then applied to the analysis of hemodynamical features involved with cerebral aneurysm pathology. ITP is implemented in the fdatest R package
Multi-aspect local inference for functional data: Analysis of ultrasound tongue profiles
Full text linkMotivated by the analysis of a data set of ultrasound tongue profiles, we present multi-aspect interval-wise testing (IWT), i.e., a local nonparametric inferential technique for functional data embedded in Sobolev spaces. Multi-aspect IWT is a nonparametric procedure that tests differences between groups of functional data, jointly taking into account the curves and their derivatives. Multi-aspect IWT provides adjusted multi-aspect
-value functions that can be used to select intervals of the domain that are imputable for the rejection of a null hypothesis. As a result, it can impute the rejection of a functional null hypothesis to specific intervals of the domain and to specific orders of differentiation. We show that the multi-aspect
-value functions are provided with a control of the family-wise error rate and that they are consistent. We apply multi-aspect IWT to the analysis of a data set of tongue profiles recorded for a study on Tyrolean, a German dialect spoken in South Tyrol. We test differences between five different ways of articulating the uvular /r/: vocalized /r/, approximant, fricative, tap, and trill. Multi-aspect IWT-based comparisons result in an informative and detailed representation of the regions of the tongue where a significant difference occurs
Hotelling’s T2 in separable Hilbert spaces
No full textWe address the problem of finite-sample null hypothesis significance testing on the mean element of a random variable that takes value in a generic separable Hilbert space. For this purpose, we propose a (re)definition of Hotelling’s T2
that naturally expands to any separable Hilbert space that we further embed within a permutation inferential approach. In detail, we present a unified framework for making inference on the mean element of Hilbert populations based on Hotelling’s T2
statistic, using a permutation-based testing procedure of which we prove finite-sample exactness and consistency; we showcase the explicit form of Hotelling’s T2
statistic in the case of some famous spaces used in functional data analysis (i.e., Sobolev and Bayes spaces); we demonstrate, by means of simulations, that Hotelling’s T2
exhibits the best performances in terms of statistical power for detecting mean differences between Gaussian populations, compared to other state-of-the-art statistics, in most simulated scenarios; we propose a case study that demonstrate the importance of the space into which one decides to embed the data; we provide an implementation of the proposed tools in the R package fdahotelling available at https://github.com/astamm/fdahotelling
Machine perfusion techniques for liver transplantation - A meta-analysis of the first seven randomized-controlled trials
No full textBackground & aims: Machine perfusion is increasingly being tested in clinical transplantation. Despite this, the number of large prospective clinical trials remains limited. The aim of this study was to compare the impact of machine perfusion vs. static cold storage (SCS) on outcomes after liver transplantation. Methods: A systematic search of MEDLINE, EMBASE, CINAHL and the Cochrane Central Register of Controlled Trials (CENTRAL) was conducted to identify randomized-controlled trials (RCTs) comparing "post-transplant" outcomes following machine perfusion vs. SCS. Data were pooled using random effect models. Risk ratios (RRs) were calculated for relevant outcomes. The quality of evidence was rated using the GRADE-framework. Results: Seven RCTs were identified (four on hypothermic oxygenated [HOPE] and three on normothermic machine perfusion [NMP]), including a total number of 1,017 patients. Both techniques were associated with significantly lower rates of early allograft dysfunction (NMP: n = 41/282, SCS: n = 74/253, RR 0.50, 95% CI 0.30-0.86, p = 0.01, I2 = 39%; HOPE: n = 45/241, SCS: n = 97/241, RR 0.48, 95% CI 0.35-0.65, p < 0.00001, I2 = 5%). The HOPE approach led to a significant reduction in major complications (Clavien Grade ≥IIIb; HOPE: n = 90/241; SCS: n = 117/241, RR 0.76, 95% CI 0.63-0.93, p = 0.006, I2 = 0%), "re-transplantation" (HOPE: n = 1/163; SCS: n = 11/163; RR 0.21, 95% CI 0.04-0.96, p = 0.04; I2 = 0%) and graft loss (HOPE: n = 7/163; SCS: n = 19/163; RR 0.40, 95% CI 0.17-0.95, p = 0.04; I2 = 0%). Both perfusion techniques were found to 'likely' reduce overall biliary complications and non-anastomotic strictures. Conclusions: Although this study provides the highest current evidence on the role of machine perfusion, outcomes remain limited to a 1-year follow-up after liver transplantation. Comparative RCTs and large real-world cohort studies with longer follow-up are required to enhance the robustness of the data further, thereby supporting the introduction of perfusion technologies into routine clinical practice. Prospero-registration: CRD42022355252. Impact and implications: For a decade, two dynamic perfusion concepts have increasingly been tested in several transplant centres worldwide. We undertook the first systematic review and meta-analysis and identified seven published RCTs, including 1,017 patients, evaluating the effect of machine perfusion (hypothermic and normothermic perfusion techniques) compared to static cold storage in liver transplantation. Both perfusion techniques were associated with lower rates of early allograft dysfunction in the first week after liver transplantation. Hypothermic oxygenated perfusion led to a reduction in major complications, lower "re-transplantation" rates and better graft survival. Both perfusion strategies were found to 'likely' reduce overall biliary complications and non-anastomotic biliary strictures. This study provides the highest current evidence on the role of machine perfusion. Outcomes remain limited to a 1-year post-transplant follow-up. Larger cohort studies with longer follow-up and clinical trials comparing the perfusion techniques are required. This is especially relevant to provide clarity and optimise implementation processes further to support the commissioning of this technology worldwide
Continuous Crossover Femoropopliteal Bypass Is an Unusual Route when Revascularisation Seems Impossible
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