bluuebunny/crossref_metadata_2025_split huggingface dataset:
A quantitative study of the bias in estimating the treatment effect caused by omitting a balanced covariate in survival models
Authors: Chastang Claude , Byar David , Piantadosi Steven 
Published: April 2007

AbstractThis paper discusses the quantitative aspects of bias in estimates of treatment effect in survival models when there is failure to adjust on balanced prognostic variables. A simple numerical example of this bias is given along with approximate formulae for its calculation in the multiplicative exponential survival model. The accuracy of the formulae is checked by simulation. In addition, approximate calculations and simulations of power loss and the effects of omitting more than one prognostic covariate are presented. The Weibull and Cox models are also examined using simulation. Study of this bias is pertinent to much applied work, and shows that the effect of omitting balanced covariates can be modest unless the variables are strongly prognostic or many in number. This work emphasizes the need for thorough comparisons of adjusted and unadjusted analyses for sensible interpretation of treatment effects.
Non‐parametric analysis of treatment—covariate interaction in the presence of censoring
Authors: Schemper M. 
Published: April 2007

AbstractThe demonstration of varying treatment efficacy among different subsets of patients is an important part of the analysis of clinical trials. The paper commences by clarifying the meaning of interaction and by reviewing valid procedures of analysis in the presence of interaction. Suitable descriptive measures of treatment—covariate interactions are (ratios of) hazard ratios to which generalized Patel—Hoel tests for qualitative or ordinal categorical covariates are related. Both the hazard ratios and the tests are given in a formulation for use with different scoring systems such as u‐ or e. Furthermore, the procedures are related to common k‐sample tests and thus are suitable for proportional and for converging hazards. A worked example is included.
On sample sizes to estimate the protective efficacy of a vaccine
Authors: O'neill Robert T. 
Published: April 2007

AbstractTo estimate vaccine protective efficacy, defined as VE = 1 — ARV/ARU where ARV is the disease attack rate in the vaccinated group and ARU is the disease attack rate in the controls, investigators have used both cohort and case‐control designs. For each design, we present a method for calculation of the sample size required to provide an approximate confidence interval for VE of predetermined width and probability of coverage. The required sample size is a function of the desired width of the confidence interval, the probability of coverage, the assumed VE, and, for cohort designs, the assumed disease attack rate in the controls, and for case‐control designs, the assumed vaccine exposure prevalence for the controls.
Beyond sensitivity, specificity and statistical independence
Authors: Jones Richard H. , McClatchey Maureen W. 
Published: April 2007

AbstractSensitivity and specificity have clear definitions when there is a single test for one disease, and the test is either positive or negative. This paper presents a unified appraoch for obtaining posterior probabilities (predictive values) when there are more than two test outcomes and/or more than one disease state. In these cases, sensitivity and specificity do not have clear definitions. Three examples from the literature demonstrate how this approach simplifies the presentation of Bayesian revision of prior probabilities. Use of proper care in data collection for the purpose of estimating conditional probabilities can avoid assumptions of statistical independence.
Doubling the one‐sided p‐value in testing independence in 2 × 2 tables against a two‐sided alternative
Authors: Lloyd Christopher J. 
Published: April 2007

AbstractDupont investigated the advantages of doubling the one‐sided P‐value in conducting a two‐sided test of independence in a 2 × 2 table and claimed that the main advantage was that, unlike the ‘exact’ P‐value, small changes in the table resulted in small changes in the significance. He admitted that this practice had no obvious theoretical justification. In this paper, I take the view that repeated sampling properties should form the basis of any such justification. I develop an appropriate framework for studying P‐values and show that doubling the one‐sided P‐value produces a biased test whenever the table is asymmetric. I show how one may derive a slightly more complicated P‐value from a uniformly most powerful test. While there are difficulties in interpreting these P‐values, I argue that, in principle, one should prefer the latter. In practice the difference between the two is typically less than 10 per cent (for the tables Dupont considered, the difference is of the order of 1 per cent) but with highly skew tables the difference can be much larger.
Adjusting for baseline: Change or percentage change?
Authors: Kaiser Lee 
Published: April 2007

AbstractClinical trials data often include baseline and response measurements on each patient. Comparisons of treatments commonly employ either change from baseline or percentage change from baseline as the analysis variable. This paper provides guidance on the choice between these two by means of plots of these variables versus baseline. I provide two examples that illustrate the problem and I discuss the impact of use of the wrong adjusted response.
A discussion on the conventional estimator of sensitivity and specificity in multiple tests
Authors: Lui Kung‐Jong 
Published: April 2007

AbstractBoth the variation of positive responses (negative responses) among individuals and the internal correlation among responses for the same individual affect the precision of the estimate of sensitivity (specificity). To estimate the sensitivity (specificity) of a medical diagnostic test, this paper proposes a Bayesian approach with a simple Markov model to evaluate the performance of the conventional estimator under different situations. On the basis of the assumed model, we derive a general formula for the variance of the conventional estimator regarding multiple tests and present a quantitative discussion on the limitations of this estimator.
Survival analysis in natural history studies of disease
Authors: Cnaan Avital , Ryan Louise 
Published: April 2007

AbstractClinicians often wish to use data from clinical trials or hospital databases to study disease natural history. Of particular interest are estimated survival and prognostic factors. In this context, it may be appropriate to measure survival from diagnosis or some other time origin, possibly prior to study entry. We describe the application of methods for truncated survival data, and compare these with the standard product limit estimator and proportional hazards models in the measurement of survival from entry. Theoretical considerations suggest that analysis of survival from entry may under‐ or overestimate the survival distribution of interest, depending on the shape of the true underlying hazard. Analogous results hold for the coefficients from a proportional hazards model. We illustrate our findings with data from a multicenter clinical trial and a hospital database.
On the statistical analysis of ROC curves
Authors: Thompson M. L. , Zucchini W. 
Published: April 2007

AbstractWe introduce a new accuracy index for receiver operating characteristic (ROC) curves, namely the partial area under the binormal ROC graph over any specified region of interest. We propose a simple but general procedure, based on a conventional analysis of variance, for comparing accuracy indices derived from two or more different modalities. The proposed method is related to and compared with existing methodology, and is illustrated by results from an experiment on optimization of density and contrast yielded by multiform photographic images used for scintigraphy.
Mixture models for partially unclassified data: A case study of renal venous renin in hypertension
Authors: McLachlan G. J. , Gordon R. D. 
Published: April 2007

AbstractIn many applications of discriminant analysis in medicine, data of known origin which can be reasonably assumed to be a random sample from the entire class may not be available for each of the possible classes. In this paper we note how such situations can be handled by using finite mixture models to formulate the estimation problem. This approach is adopted to model the distribution of the renal venous renin ratio (RVRR) between left and right kidneys in patients with hypertension. This distribution is used in the formation of a probabilistic allocation rule as an aid in the diagnosis of renal artery stenosis, which is potentially curable by surgery.
Changes in executive compensation following an environmental shift: the role of top management team turnover
Authors: Cho Theresa S. , Shen Wei 
Published: April 2007

AbstractIn this study we examine the changes in executive compensation at the top management team (TMT) level following an environmental shift. Using the context of deregulation in the airline industry, we find that: (1) a dramatic environmental change that heightens managerial discretion leads to greater pay level and performance sensitivity of TMT compensation; and (2) the greater the magnitude of turnover among TMT members following the environmental shift, the greater the compensation change. Copyright © 2007 John Wiley & Sons, Ltd.
Acquisitions of private vs. public firms: Private information, target selection, and acquirer returns
Authors: Capron Laurence , Shen Jung‐Chin 
Published: April 2007

AbstractThe acquisition of privately held firms is a prevalent phenomenon that has received little attention in mergers and acquisitions research. In this study, we examine three questions: (1) What drives the acquirer's choice between public and private targets? (2) Do acquisitions of private targets elicit a more positive stock market reaction than acquisitions of public targets, which, on average, destroy value for acquirers' shareholders? (3) Do acquirers gain when their selection of a public or private target fits the theory? In this paper, we argue that the lack of information on private targets limits the breadth of the acquirer's search and increases its risk of not evaluating properly the assets of private targets. At the same time, less information on private targets creates more value‐creating opportunities for exploiting private information, whereas the market of corporate control for public targets already serves as an information‐processing and asset valuation mechanism for all potential bidders. Using an event study and survey data, we find that: (1) acquirers favor private targets in familiar industries and turn to public targets to enter new business domains or industries with a high level of intangible assets; (2) acquirers of private targets perform better than acquirers of public targets on merger announcement, after controlling for endogeneity bias; (3) acquirers of private firms perform better than if they had acquired a public firm, and acquirers of public firms perform better than if they had acquired a private firm. These results support the expectation that acquirer returns from their target choice (private/public) are not universal but depend on the acquirer's type of search and on the merging firms' attributes. Copyright © 2007 John Wiley & Sons, Ltd.
Market orientation and performance
Authors: Connor Tom 
Published: April 2007

AbstractThis response is prompted by Hult, Ketchen and Slater's (2005) article entitled ‘Market orientation and performance: an integration of disparate approaches.’ As a contributor to the foregoing debate in the pages of this journal to which they refer I am writing to offer some observations on the nature and implications of the research reported in their paper and to clarify my essential difficulty as a strategist with the ‘market‐oriented: customer‐led’ construct. Copyright © 2007 John Wiley & Sons, Ltd.
XAS analysis on mesoporous vanadium oxide thin films by sol‐gel
Authors: Cremonesi A. , Calestani G. , Antonioli G. , Bersani D. , Lottici P. P. , Djaoued Y. , Brüning R. 
Published: April 2007

AbstractIn this work an extended x‐ray absorption fine structure (EXAFS) analysis on sol‐gel derived VOx thin films, templated using polyethylene glycol (PEG), is reported. The results, together with previous Raman and x‐ray diffraction (XRD) investigation, indicate two different structures for our samples: the first is characterized by a nearly 3D network with both axial and planar order, while the second has a 2D‐character with short range order. Copyright © 2007 John Wiley & Sons, Ltd.
Civilian Extraperitoneal Rectal Gunshot Wounds: Surgical Management Made Simpler
Authors: Navsaria Pradeep H. , Edu Sorin , Nicol Andrew J. 
Published: April 2007

AbstractBackgroundRectal injuries are associated with significant morbidity and mortality. Controversy persists regarding routine presacral drainage, distal rectal washout (DRW), and primary repair of extraperitoneal rectal injuries. This retrospective review was performed to determine the outcome of rectal injuries in an urban trauma center with a high incidence of penetrating trauma where a non‐aggressive surgical approach to these injuries is practiced.MethodsThe records of all patients with a full‐thickness penetrating rectal injury admitted to the Trauma Center at Groote Schuur Hospital over a 4‐year period were reviewed. These were reviewed for demographics, injury mechanism and perioperative management, anatomical site of the rectal injury, associated intra‐abdominal injuries and their management. Infectious complications and mortality were noted. Intraperitoneal rectal injuries were primarily repaired, with or without fecal diversion. Extraperitoneal rectal injuries were generally left untouched and a diverting colostomy was done. Presacral drainage and DRW were not routinely performed.ResultsNinety‐two patients with 118 rectal injuries [intraperitoneal (7), extraperitoneal (59), combined (26)] were identified. Only two extraperitoneal rectal injuries were repaired. None had presacral drainage. Eighty‐six sigmoid loop colostomies were done. Two (2.2%) fistula, one rectocutaneous, and one rectovesical, were recorded. There were nine (9.9%) infectious complications: surgical site infection (4), buttock abscess (1), buttock necrosis (1), pubic ramus osteitis (1), septic arthritis (2). No perirectal sepsis occurred.ConclusionsExtraperitoneal rectal injuries due to low‐velocity trauma can be safely managed by fecal diversion alone.
Interaction between parallel Gaussian electromagnetic beams in ionic collision dominated plasmas with thermal conduction
Authors: SODHA MAHENDRA SINGH , AGARWAL SUJEET KUMAR , SHARMA ASHUTOSH 
Published: April 2007

AbstractIn this communication the interaction between two Gaussian electromagnetic beams in an ionic collision dominated plasma has been investigated, when the axes of the two beams are initially (z = 0) parallel along the z-axis in the xz plane; the beams are initially propagating in the z-direction. Taking into account the loss of electron energy by collisions and by thermal conduction, the energy balance equation for electrons has been solved to obtain the space dependence of the electron temperature and the dielectric function has been expressed as a function of the electron temperature; this expression for the dielectric function has been substituted in the wave equation and a solution of the resulting nonlinear equation obtained in the paraxial approximation. Second-order coupled ordinary differential equations have been obtained for the distance between the centers of the beams and the beam widths in the x- and y-directions as a function of the distance of propagation along the z-axis. The equations have been solved numerically for a range of parameters and a discussion of the results is presented for the case when the two beams have the same axial irradiance, frequency and width. From simple considerations it is seen that the beams attract each other when 2xo < wro and in this situation beams are close enough for the paraxial approximation to be valid.
Inhibitory deficits for negative information in persons with major depressive disorder
Authors: LAU MARK A. , CHRISTENSEN BRUCE K. , HAWLEY LANCE L. , GEMAR MICHAEL S. , SEGAL ZINDEL V. 
Published: April 2007

ABSTRACTBackgroundWithin Beck's cognitive model of depression, little is known about the mechanism(s) by which activated self-schemas result in the production of negative thoughts. Recent research has demonstrated that inhibitory dysfunction is present in depression, and this deficit is likely valence-specific. However, whether valence-specific inhibitory deficits are associated with increased negative cognition and whether such deficits are specific to depression per se remains unexamined. The authors posit the theory that inhibitory dysfunction may influence the degree to which activated self-schemas result in the production of depressive cognition.MethodIndividuals with major depressive disorder (MDD, n=43) versus healthy (n=36) and non-depressed anxious (n=32) controls were assessed on the Prose Distraction Task (PDT), a measure of cognitive inhibition, and the Stop-Signal Task (SST), a measure of motor response inhibition. These two tasks were modified in order to present emotionally valenced semantic stimuli (i.e. negative, neutral, positive).ResultsParticipants with MDD demonstrated performance impairments on the PDT, which were most pronounced for negatively valenced adjectives, relative to both control groups. Moreover, these impairments correlated with self-report measures of negative thinking and rumination. Conversely, the performance of the MDD participants did not differ from either control group on the SST.ConclusionsImplications of these findings for understanding the mechanisms underlying the development and maintenance of depressive cognition are discussed.
Austrian Breast and Colorectal Cancer Study Group (ABCSG)
Authors:   The Breast International Group
Published: April 2007

This section provides current contact details and a summary of recent or ongoing clinical trials being coordinated by Austrian Breast and Colorectal Cancer Study Group ABCSG. Clinical trials include:Adjuvant therapy with CMF versus goserelin plus tamoxifen in pre-menopausal, hormone-responsive, lymph node-positive or -negative patients. Study 5Adjuvant endocrine therapy in postmenopausal patients with hormone-responsive breast cancer: tamoxifen versus tamoxifen plus aminoglutethimide. Study 6Pre and postoperative chemotherapy versus conventional adjuvant chemotherapy alone in patients presenting with hormone receptor-negative breast cancer. Study 7Adjuvant endocrine therapy in postmenopausal patients with hormone-responsive breast cancer, G1 and G2 (ARNO). Study 8Adjuvant chemotherapy in postmenopausal patients with hormone-responsive breast cancer, G3. Study 9Adjuvant endocrine therapy and bisphosphonate therapy: tamoxifen in comparison to anastrozole, alone or in combination with zoledronate, in premenopausal patients presenting with hormone-responsive, Stage I and II breast cancer. Study 12Effect of 3 versus 6 cycles of epidoxorubicin/docetaxel G-CSF upon the rate of complete pathological remissions in the neoadjuvant treatment of patients with primary breast cancer and no distant metastases. Study 14SALSA (Secondary Adjuvant Long-term Study with Arimidex): a prospective, randomized, open, multicentre Phase III study to assess the efficacy of secondary adjuvant endocrine anastrozole therapy for 2 further years versus 5 further years in patients with hormone receptor-positive breast cancer after a 5-year primary adjuvant endocrine therapy. Study 16Neoadjuvant hormonal therapy with exemestane in postmenopausal patients with primary hormone receptor-positive breast cancer and no distant metastases. Study 17A randomized, double-blind, placebo-controlled, multi-centre phase 3 study to determine the treatment effect of denosumab in subjects with non-metastatic breast cancer receiving aromatase inhibitor therapy. Study 18A randomised Phase II study comparing anastrozole and fulvestrant to anastrozole for adjuvant treatment of postmenopausal patients with early breast cancer and disseminated tumour cells in bone marrow. Study 21A randomized Phase III study comparing epirubicin, docetaxel and capecitabine G-CSF to epirubicin and docetaxel G-CSF as neoadjuvant treatment for early HER-2 negative breast cancer and comparing epirubicin, docetaxel and capecitabine G-CSF trastuzumab to epirubicin and docetaxel G-CSF trastuzumab as neoadjuvant treatment for early HER-2 positive breast cancer. Study 24
Adjuvant Tamoxifen – Longer Against Shorter (ATLAS)
Authors:   The Breast International Group
Published: April 2007

This section provides current contact details and a summary of recent or ongoing clinical trials being coordinated by Adjuvant tamoxifen – longer against shorter (ATLAS). Clinical trials include:
Phase III ATLAS adjuvant tamoxifen – longer against shorter: an international trial of adjuvant hormonal treatment duration (www.ctsu.ox.ac.uk/~atlas/index.html).
Fondazione Michelangelo Breast Cancer Group (FM-B)
Authors:   The Breast International Group
Published: April 2007

This section provides current contact details and a summary of recent or ongoing clinical trials being coordinated by Fondazione Michelangelo Breast Cancer Group (FM-B). Clinical trials include:
European cooperative study of chemotherapy and surgery comparing adjuvant doxorubicin followed by CMF versus adjuvant doxorubicin/paclitaxel followed by CMF versus primary doxorubicin/paclitaxel followed by CMF in women with operable breast cancer and T > 2cm.European Cooperative Study of Primary Systemic Therapy in Women with Operable Breast Cancer and T > 2cm.
Grupo de Estudios Clínicos Oncológicos del Perú (GECO PERU)
Authors:   The Breast International Group
Published: April 2007

This section provides current contact details and a summary of recent or ongoing clinical trials being coordinated by Grupo de Estudios Clínicos Oncológicos del Perú (GECO PERU). Clinical trials include:
Determination of prognostic factors in the outcome to a metronomic treatment with low doses of cyclophosphamide and methotrexate in patients with advanced breast cancer.
National Surgical Adjuvant Breast and Bowel Project (NSABP)
Authors:   The Breast International Group
Published: April 2007

This section provides current contact details and a summary of recent or ongoing clinical trials being coordinated by National Surgical Adjuvant Breast and Bowel Project (NSABP). Clinical trials include:
NSABP B-35 – A clinical trial comparing anastrozole with tamoxifen in postmenopausal patients with ductal carcinoma in situ (DCIS) undergoing lumpectomy with radiation therapy.NSABP B-36 – A clinical trial of adjuvant therapy comparing six cycles of 5-fluorouracil, epirubicin and cyclophosphamide (FEC) to four cycles of adriamycin and cyclophosphamide (AC) in patients with node-negative breast cancer.NSABP B-38 – A phase III, adjuvant trial comparing three chemotherapy regimens in women with node-positive breast cancer: docetaxel/doxorubicin/cyclophosphamide (TAC); dose-dense (DD) doxorubicin/cyclophosphamide followed by DD paclitaxel (DD AC→P): DD AC followed by DD paclitaxel plus gemcitabine (DD AC→PG).NSABP B-39 – A randomized phase III study of conventional whole breast irradiation (WBI) versus partial breast irradiation (PBI) for women with stage 0, I, or II breast cancer.