1,720,979 research outputs found
Note statistiche. Curve di rischio istantaneo di morte : il loro ruolo nella decisione clinica del cardiologo
No full textNegli studi di lunga durata (follow-up) l’interesse del ricercatore è volto soprattutto a cogliere l’andamento nel tempo dell’accadimento delle morti. Questa nota statistica ha come oggetto i metodi dell’analisi della sopravvivenza, strumento di elezione per trattare questo tipo di dati. Si introducono qui la curva di sopravvivenza, la curva cumulativa di mortalità, la curva del rischio istantaneo di morte ed un pertinente indicatore di rischio relativo: l’hazard ratio. L’utilizzo di quest’ultimo è illustrato per mezzo della sperimentazione clinica controllata randomizzata TARGET
Sample size for recurrent events data in non randomized studies with an historical control
No full textIn some exceptional circumstances, as in very rare diseases, non randomised trials with historical controls may be the only way to demonstrate efficacy and safety of a new treatment. The design of such studies needs a sound methodological approach in order to provide a good level of scientific evidence. To our knowledge, no attention has been given to the development of methods for sample size calculation for non randomized controlled trials (one treatment arm) where the end-point deals with recurrent events. In this context, guidelines for study design, including formulas for sample size, were only proposed for the typical scenario of randomized clinical trial (Bernardo and Harrington, 2001; Cook and Wei, 2003; Matsui, 2005). Here we propose an approach to power and sample size calculation for non randomised trials with historical controls that relies on simulation studies. Non parametric tests statistics will be considered, with the rate of events of the historical control as a reference. We will also develop an extension that accounts for paired comparisons in cases where information on pre-treatment event history of patients is available. Simulations will explore different models for the underlying event generation process (i.e. homogeneous, non homogeneous, mixed Poisson process) in order to evaluate the robustness of sample size calculation. The approach will be illustrated with a non randomized trial on experimental gene therapy in a very rare immunodeficiency (ADA-SCID), where a major end-point is the history of recurrent severe infections
Note statistiche. A quali rischi espone i propri pazienti il cardiologo che accetta di partecipare ad una sperimentazione clinica senza un'approfondita riflessione sulle evidenze disponibili a priori?
No full textThe aim of this statistical note is to describe the results of the randomized controlled clinical trial TARGET, which compared the effect of tirofiban (new treatment) and abciximab (standard treatment) in patients who were expected to undergo coronary stenting. Primary aim of TARGET was to evaluate the non-inferiority of tirofiban with respect to abciximab, but it concluded in favor of superiority of the standard treatment. The authors of this study point out that a deep consideration regarding a priori available evidence could have avoided to expose 2398 patients randomized to tirofiban to the risk of death or non-fatal myocardial infarction
Note statistiche. Sperimentazioni cliniche controllate randomizzate sia di superiorità che di non-inferiorità : considerazioni critiche
No full textScopo di questa nota statistica, la quarta della serie, è descrivere e discutere criticamente la sperimentazione
clinica controllata randomizzata (SCCR) GUSTO V, che costituisce un tentativo di combinare in una sola sperimentazione le due tipologie di SCCR di superiorità e di non inferiorità. In questa nota si descrive il percorso logico che gli autori hanno seguito per la programmazione della SCCR sia di superiorità che di non inferiorità e se ne presentano i risultati. Inoltre si mettono
in luce i possibili aspetti critici di una SCCR programmata in tal modo e si chiede al lettore di riflettere a riguardo
Analysis of recurrent complications with intermittent exposure and time-varying treatment in cancer
No full textCancer treatment usually induces a depression of the immune system, that may cause neutropenic periods in which the patient is exposed to an increased risk of infections and sever complications, typically announced by fever (common symptom). A prospective observational study conducted between 2002 and 2004 at the Gaslini Hospital in Italy gathered information on neutropenic periods of 157 children affected by different types of solid tumours, receiving chemotherapy regimens (classified into two broad categories, very intensive and intensive) and, possibly, autologous hemopoietic stem cell transplantation. The aim was to asses the role of treatment in the incidence of recurrent febrile complications during neutropenic periods, accounting for the history of past events, the intermittence of exposure and the time-varying nature of treatment.
We considered a stratified Cox model for a marginal and frailty analysis, stratified by type of cancer, with age and sex as fixed covariates and treatment as a time-dependent covariate. The results suggested that patients who underwent transplantation were more likely to develop febrile episodes. Unmeasured heterogeneity between patients did not appear to be relevant and results of the frailty model were very similar to that of the marginal model. The need to evaluate how the history of previous febrile episodes impacts on the current risk of developing fever requires further developments. In particular, the approach explored in this regard is the Aalen’s Additive Hazard model, that may be useful to disentangle the role of treatment and the influence of previous events
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Timing of Familial Breast Cancer in Sisters
No full textBackground: Women who have had a first-degree relative diagnosed with breast cancer (ie, a positive family history) have a rate of breast cancer that is approximately twice that of all women their age, but it is unclear how they should perceive this risk at different ages or if they should be considered at higher risk for the remainder of their lifetime.
Methods: We used Swedish population–based data to assess the risk of breast cancer in 23654 sisters of women diagnosed with breast cancer and in 1 732 775 sisters of unaffected women from 1958 through 2001. Poisson models were used to express the rate of breast cancer as a function of current age, whether a woman had an affected sister, time since the first diagnosis in the family, and family size (number of sisters). The effect of the age of the index case (the first sister diagnosed in the family) at diagnosis and whether her "at-risk" sisters had achieved this age were examined in stratified analyses. Incidence rate ratios of breast cancer in exposed compared with unexposed sisters were calculated with 95% confidence intervals. All estimates were adjusted for calendar time.
Results: Sisters of breast cancer patients had higher breast cancer incidence than unexposed sisters at all ages. The association of exposure (ie, a diagnosis of breast cancer in a sister) with the risk of breast cancer was most pronounced in young women (age 20–39; incidence rate ratio = 6.64, 95% confidence interval = 4.66 to 9.48), and the relative risk decreased to approximately 2 in women older than 50 years. The risk associated with having a sister diagnosed with breast cancer was not modified substantially by the age of the index case at diagnosis (≤45 years vs >45 years). The risk was similar for women who were approaching the age at which the first sister was diagnosed in their family and those who had already attained it. The incidence rate ratio of breast cancer in exposed sisters compared with unexposed sisters was constant over time for all age categories of at-risk women.
Conclusions: Women who have a sister diagnosed with breast cancer have an increased risk of breast cancer throughout much of their lifetimes
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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