1,720,956 research outputs found
Estimation of the effect of interventions that modify treatment
No full textMotivated by a study of surgical operating time and post-operative outcomes for lung cancer, we consider the estimation of causal effects of continuous point-exposure treatments. To investigate causality, the standard paradigm postulates a series of treatment-specific counterfactual outcomes and establishes conditions under which we may learn about them from observational study data. While many choices are possible, causal effects are typically defined in terms of variation of the mean of counterfactual outcomes in hypothetical worlds in which specific treatment strategies are ‘applied’ to all individuals. For example, one might compare two worlds: one where each individual receives some specific dose and a second where each individual receives some other dose. For our motivating study, defining causal effects in this way corresponds to (hypothetical) interventions that could not conceivably be implemented in the real world. In this work, we consider an alternative, complimentary framework that investigates variation in the mean of counterfactual outcomes under hypothetical treatment strategies where each individual receives a treatment dose corresponding to that actually received but modified in some pre-specified way. Quantification of this variation is defined in terms of contrasts for specific interventions as well as in terms of the parameters of a new class of marginal structural mean models. Within this framework, we propose three estimators: an outcome regression estimator, an inverse probability of treatment weighted estimator and a doubly robust estimator. We illustrate the methods with an analysis of the motivating data.Fil: Haneuse, Sebastian. Harvard University; Estados UnidosFil: Rotnitzky, Andrea Gloria. Universidad Torcuato Di Tella. Departamento de Economía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
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
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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Comparative Safety and Effectiveness of Anticonvulsants Among Older Adults
No full textAnticonvulsant use among older adults has increased 200-fold over the past 25 years.1 In our previous work, we estimated that one in eight older adults in the US are currently receiving anticonvulsants.2 The risk of adverse events approaches 20%, and 5% of them are potentially life-threatening.2-4 Older adults with Alzheimer’s disease and Alzheimer’s-related dementias (AD/ADRD) are more susceptible to these adverse effects.5-10 The most common indications for anticonvulsants are seizure prophylaxis, insomnia, pain, and agitation, which are all common conditions among older adults who survive an Acute Ischemic Stroke (AIS).11,12 In the US alone there are 7 million stroke survivors, and 800,000 new or recurrent stroke cases annually.11,13-15
The increasing in-hospital use of neurophysiology studies has led to greater detection of epileptiform abnormalities of uncertain clinical significance, greater perceived seizure risk, and increasing prescriptions of seizure prophylaxis with drugs like levetiracetam or phenytoin.16-19 Additionally, the rate of prescriptions of benzodiazepines for patients with post-AIS insomnia, periprocedural anxiety, and delirium (often manifested with agitation) continues to rise.2,20-23 In the meantime, major medical and psychiatric organizations suggest avoidance of anticonvulsants in those ≥65 years.2,20-28
Rigorous evidence is urgently needed about the effectiveness and safety of these drugs for older adults.5-10 However, randomized trials arguably are impractical because of large numbers needed for safety studies, the high cost of such studies, and difficulty recruiting older adults into clinical trials. Prior observational studies have severe limitations: small samples, poor data granularity and validity, selection bias, and confounding by indication. Many factors may be associated with anticonvulsant initiation, including socio-demographic, clinical, and health-care utilization characteristics.29-32
To overcome these challenges, we linked data from a prospective stroke registry (Get-With-The Guidelines-Stroke) to comprehensive electronic health records (EHRs) and applied novel statistical methods to evaluate the effects of treatment initiation strategies among adults ≥65 years who are survivors of an AIS on adverse health outcomes, initially focusing on mortality in the next months. Moreover, to enable later work toward this overall goal in national Medicare data, we conducted a validation study linking Medicare claims and EHRs to optimize claims-based definitions of AD/ADRD, an important stratification measure.
In Chapter 1, we examined the accuracy of claims-based diagnoses of AD/ADRD with respect to expert clinician adjudication using a novel database with individual-level linkages between electronic health record (EHR) and claims. A model that regressed reference standard dementia on a refined-count definition (i.e., the number of days with a qualifying diagnostic claims), and included age and sex, had excellent calibration to the reference standard with calibration-in-the-large [CV CITL] .001 and calibration slope of 0.97. The adjudicated prevalence of dementia was 7% (n=2854, 95%CI: 6%-9%) in the target population. Using a predicted probability threshold of 0.5 to classify dementia, that model demonstrated negative predictive value of 90.1% (SD 0.5%), positive predictive value of 77.1% (SD 2.0%), sensitivity of 68.0% (SD 1.8%), and specificity of 93.5% (SD 0.7%).
Next, we linked the prospective stroke registry to EHRs and examined the comparative effectiveness and safety of benzodiazepines and seizure prophylaxis initiation strategies among older adults post-AIS. In Chapter 2, we focused on benzodiazepine prescriptions, which are typically short-term (i.e., one or few doses) used to treat insomnia and agitation, and may cause serious adverse effects within few hours of initiation. In Chapter 3, we switched the focus to examine anticonvulsants given for seizure prophylaxis, which are often prescribed for 30-90 days or more, and may cause serious adverse effects within days or weeks of initiation.
Specifically, in Chapter 2, we examined the difference in 30-day mortality risk associated with initiating benzodiazepines within seven days after an AIS compared with no benzodiazepines among patients ≥65 years. We concluded that in the overall population the excess in mortality associated with initiating benzodiazepines was largely due to confounding by indication. Excess deaths per 1,000 stratified by age ranged from 2 (95% CI -16 to 12), to 12 (95% CI -9 to 143), to 20 (95% CI -43 to 81) among patients 65-74, 75-84 years, and ≥ 85 years, respectively. The RD was 1 (CI, -3 to 9) among patients with mild stroke (NIHSS ) and 18 (CI, -85 to 148) among those with moderate-to-severe stroke (NIHSS 16-20).
In Chapter 3, we examined the 90-day mortality risk associated with initiation of epilepsy-specific seizure prophylaxis within seven days after an AIS in patients ≥65 years. After standardization, the estimated mortality was 127 (95% CI, 64 to 256) and 65 (95% CI, 40 to 89) deaths per 1000 in the two strategies, corresponding to a risk difference (RD) of 62 (95% CI, -8 to 198) excess deaths per 1000 patients and a hazard ratio (HR) of 1.38 (CI, 0.60 to 3.55). Therefore, we found evidence of a potential excess in 90-day mortality associated with initiating seizure prophylaxis within seven days post-AIS compared with not initiating seizure prophylaxis in the overall population. However, the estimates were imprecise and residual confounding by indication remained a concern. In the prespecified subgroup analyses, the RD was 5 (CI, -8 to 10) among patients with minor and 88 (CI, -17 to 288) among those with moderate or severe AIS. Similarly, the RDs were 27 (95% CI -5 to 83) and 92 (95% CI -5 to 239) among patients aged 65-74 years and ≥ 75 years, respectively. The HR were similar across age and severity groups.
Our work highlights the urgent need to discuss whether older patients would benefit from or be harmed by initiation of anticonvulsant prophylaxis during the acute and post-acute stroke recovery periods. In future steps, we will examine the distribution of anticonvulsant specific outcomes as indicators of benefits (effectiveness) and harms (adverse reactions,), such as the incidence of seizure-like events and fall-related injuries and seizure-like events stratifying by care settings. We also will examine longer-term risks and benefits of other treatment indications and strategies including the comparative effectiveness and safety of specific anticonvulsants in the elderly
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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