1,720,966 research outputs found
STATISTICAL METHODS TO ANALYZE CONTINUOUS RISK VARIABLES IN INDIVIDUAL PATIENT DATA META-ANALYSES: APPLICATION ON A STUDY ON TOBACCO SMOKING AND GASTRIC CANCER RISK IN A CONSORTIUM OF CASE-CONTROL STUDIES (THE STOMACH POOLING (STOP) PROJECT)
Full text linkGastric cancer represents the fifth most common cancer and the third leading cause of cancer death over both sexes worldwide, with almost 1 million cases and over 700 000 deaths estimated in 2012. The presence of Helicobacter Pylori is a key determinant of gastric cancer. However, other factors, including familial, genetic, environmental and social characteristics appear to also have a role in the etiology of this disease. Tobacco smoking has been associated with increased risk of morbidity and mortality from many diseases and for gastric cancer. Various epidemiologic consortia have been established on several cancers but not yet on gastric cancer. A pooled-analysis of worldwide case-control studies may allow to investigate indebt gastric cancer etiology. Particularly, this large dataset will allow us to better investigate life style characteristics including tobacco smoking, in relation to gastric cancer. The Stomach cancer Pooling (StoP) Project is an international epidemiological consortium. The inclusion criteria for study participation are: a case-control study design (including nested case-control analyses derived from cohort study) and an inclusion of at least 80 cases of gastric cancer (including both cardia and non-cardia location). The aim of my project is to conduct a pooled analysis on data from already available international studies, on the role of tobacco smoking in the etiology of gastric cancer in particular, the number of cigarettes per day and the duration of smoking, using adequate statistical approaches.
During the first year of the PhD program, my project was focused on the two-stage analysis. This method is used to analyze meta-analysis and could be applicable in a case of pooled case-control analysis. The first step of the method consists in calculate adjusted study-specific odds ratios (OR) in order to overcome differences across studies in terms of design or population. The second step consists in summarize these study-specific risks using meta-analytic methods which take into account the heterogeneity across studies. During my second year of PhD program, I studied various statistical methods regarding the analysis of non-linear continuous variables. In addition to transform continuous variables in category, I considered more flexible approaches including fractional polynomials. During my third year of PhD program, I focused my research on a way to adapt these latest methods to the analysis of pooled case-control studies. In particular I chose to use factional polynomials in a two-stage method due to their simple interpretation and also because their estimates can be easily pooled through a two-stage analysis.
The first step analysis is to perform a fractional polynomial for each study. For each value of the power term (or couple of power terms for the second-order fractional polynomials), the second stage of the model is performed. The pooled dose-response relationship is estimated according to a bivariate random-effects model. The estimate of the trend components could be obtained using restricted maximum likelihood (REML) or maximum likelihood (ML) estimation. The second-stage model is fitted to the data considering each combination of the power terms. The best model, denoted by the optimal power combination is defined as the one minimizing the deviance or the Akaike Information Criterion (AIC), a penalized likelihood which takes into account the number of parameter.
We analyzed data on 21 studies including 10,040 cases and 25,602 controls. To investigate the relationship between tobacco smoking and gastric cancer risk, we first used a classical method, building categories of smokers 1) in terms of quantity; “never smokers”, “20 cigarettes per day” and 2) in terms of smoking duration; “never smokers”, “30 years of smoking”. We analyzed these variable with a two-stage method. This risk significantly increase with the number of cigarettes per day to reach an OR of 1.29 (95% CI 1.06-1.57 )for smokers of more than 20 cigarettes and, with duration to reach an OR of 1.32 (95% CI 1.17-1.49) for smokers smoking for more than 30 years compared to never smokers. These effects of increasing risk are confirmed by different statistical models of analysis including linear model and fractional polynomials, considering the number of cigarettes per day and the duration as a continuous variable.
Results from our analysis confirm that there is an association between cigarette smoking and gastric cancer risk. This risk increases with the number of cigarettes and the duration of smoking. These effects of increasing risk are confirmed by different statistical models of analysis including linear models and fractional polynomials, considering the number of cigarettes per day and the duration as continuous variables.
To our knowledge this is the first study using fractional polynomials through a two-stage random effect methods for pooled case-control studies. Through this method we were able to take into account study-specific adjustment variables and heterogeneity across studies thanks to mixed effect modeling. Categorization has the advantage of a simple epidemiologic interpretation and presentation result. However it assumes that the relationship between the risk of disease and the exposure is flat within intervals and also that there is a discontinuity in response when a category cutpoint is crossed, which is unlikely realistic. Considering exposure variables may avoid these limitations. The relationship between cigarette smoking and gastric cancer risk may be discerned from the categorical analysis, but the analysis of the variable in continuous through polynomials brought additional information in particular to understand the possible threshold and possible changes in slopes
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
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
Adherence to the Mediterranean diet and gastric cancer risk in Italy
No full textWe investigated gastric cancer risk in relation to the adherence to the Mediterranean diet using data from two case-control studies conducted in Italy between 1985 and 2007, including 999 incidents, histologically confirmed gastric cancers and 2,628 controls admitted to hospital for acute non-neoplastic diseases. Adherence to the Mediterranean diet was assessed using the Mediterranean Diet Score (MDS) based on nine of the major characteristics of the Mediterranean diet in the overall dataset. The Mediterranean Dietary Pattern adherence index (MDP) and the Mediterranean Adequacy Index (MAI) were considered in the second study only. We estimated odds ratios (OR) and corresponding 95% confidence intervals (CI) of gastric cancer for categories of the three scores using multiple logistic regression models. We found a reduced risk of gastric cancer for increasing levels of the MDS: as compared to subjects in the lowest category of the MDS, the ORs were 0.78, 0.61 and 0.57 in subsequent levels of MDS, with a significant trend in risk. Risk estimates were consistent across strata of age, sex, education, smoking, body mass index, and family history of gastric cancer. We also observed a decreased risk of gastric cancer for the highest versus the lowest quintile for MDP and MAI, with OR of 0.58 and 0.71, respectively. Our study provides convincing evidence of a beneficial role of the Mediterranean diet on gastric cancer. What's new? Adherence to the Mediterranean diet has been reported to have a beneficial effect on cardiovascular diseases and selected cancers. In this study based on data from two large Italian case-control studies, the authors considered three different scores measuring adherence to the Mediterranean diet, and found a favorable effect on gastric cancer
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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