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Standard Statistical Techniques (standard + statistical_techniques)
Selected AbstractsA latent Gaussian model for compositional data with zerosJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 5 2008Adam Butler Summary., Compositional data record the relative proportions of different components within a mixture and arise frequently in many fields. Standard statistical techniques for the analysis of such data assume the absence of proportions which are genuinely zero. However, real data can contain a substantial number of zero values. We present a latent Gaussian model for the analysis of compositional data which contain zero values, which is based on assuming that the data arise from a (deterministic) Euclidean projection of a multivariate Gaussian random variable onto the unit simplex. We propose an iterative algorithm to simulate values from this model and apply the model to data on the proportions of fat, protein and carbohydrate in different groups of food products. Finally, evaluation of the likelihood involves the calculation of difficult integrals if the number of components is more than 3, so we present a hybrid Gibbs rejection sampling scheme that can be used to draw inferences about the parameters of the model when the number of components is arbitrarily large. [source] Modeling human affective postures: an information theoretic characterization of posture featuresCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2004P. Ravindra De Silva One of the challenging issues in affective computing is to give a machine the ability to recognize the mood of a person. Efforts in that direction have mainly focused on facial and oral cues. Gestures have been recently considered as well, but with less success. Our aim is to fill this gap by identifying and measuring the saliency of posture features that play a role in affective expression. As a case study, we collected affective gestures from human subjects using a motion capture system. We first described these gestures with spatial features, as suggested in studies on dance. Through standard statistical techniques, we verified that there was a statistically significant correlation between the emotion intended by the acting subjects, and the emotion perceived by the observers. We used Discriminant Analysis to build affective posture predictive models and to measure the saliency of the proposed set of posture features in discriminating between 4 basic emotional states: angry, fear, happy, and sad. An information theoretic characterization of the models shows that the set of features discriminates well between emotions, and also that the models built over-perform the human observers. Copyright © 2004 John Wiley & Sons, Ltd. [source] Adjusting for mortality effects in chronic toxicity testing: Mixture model approachENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2000Shin Cheng David Wang Abstract Chronic toxicity tests, such as the Ceriodaphnia dubia 7-d test are typically analyzed using standard statistical methods such as analysis of variance or regression. Recent research has emphasized the use of Poisson regression or more generalized regression for the analysis of the fecundity data from these studies. A possible problem in using standard statistical techniques is that mortality may occur from toxicant effects as well as reduced fecundity. A mixture model that accounts for fecundity and mortality is proposed for the analysis of data arising from these studies. Inferences about key parameters in the model are discussed. A joint estimate of the inhibition concentration is proposed based on the model. Confidence interval estimation via the bootstrap method is discussed. An example is given for a study involving copper and mercury. [source] Effect of Off-Pump Coronary Artery Bypass Grafting on Risk-Adjusted and Cumulative Sum Failure Outcomes After Coronary Artery SurgeryJOURNAL OF CARDIAC SURGERY, Issue 6 2002Richard J. Novick M.D. We therefore applied CUSUM, as well as standard statistical techniques, to analyze a surgeon's experience with off-pump coronary artery bypass grafting (OPCAB) and on-pump procedures to determine whether the two techniques have similar or different outcomes. Methods: In 320 patients undergoing nonemergent, first time coronary artery bypass grafting, preoperative patient characteristics, rates of mortality and major complications, and ICU and hospital lengths of stay were compared between the on-pump and OPCAB cohorts using Fisher's exact tests and Wilcoxon two sample tests. Predicted mortality and length of stay were determined using previously validated models of the Cardiac Care Network of Ontario. Observed versus expected ratios of both variables were calculated for the two types of procedures. Furthermore, CUSUM curves were constructed for the on-pump and OPCAB cohorts. A multivariable analysis of the predictors of hospital length of stay was also performed to determine whether the type of coronary artery bypass procedure had an independent impact on this variable. Results: The predicted mortality risk and predicted hospital length of stay were almost identical in the 208 on-pump patients ( 2.2 ± 3.9% ; 8.2 ± 2.5 days) and the 112 OPCAB patients ( 2.0 ± 2.2% ; 7.8 ± 2.1 days). The incidence of hospital mortality and postoperative stroke were 2.9% and 2.4% in on-pump patients versus zero in OPCAB patients (p= 0.09 and 0.17, respectively). Mechanical ventilation for greater than 48 hours was significantly less common in OPCAB (1.8%) than in on-pump patients (7.7%, p= 0.04). The rate of 10 major complications was 14.9% in on-pump versus 8.0% in OPCAB patients (p= 0.08). OPCAB patients experienced a hospital length of stay that was a median of 1.0 day shorter than on-pump patients (p= 0.01). The observed versus expected ratio for length of stay was 0.78 in OPCAB patients versus 0.95 in on-pump patients. On CUSUM analysis, the failure curve in OPCAB patients was negative and was flatter than that of on-pump patients throughout the duration of the study. Furthermore, OPCAB was an independent predictor of a reduced hospital length of stay on multivariable analysis. Conclusions: OPCAB was associated with better outcomes than on-pump coronary artery bypass despite a similar predicted risk. This robust finding was documented on sensitive CUSUM analysis, using standard statistical techniques and on a multivariable analysis of the independent predictors of hospital length of stay.(J Card Surg 2002;17:520-528) [source] Statistical issues in the assessment of health outcomes in children: a methodological reviewJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 4 2009Gillian A. Lancaster Summary., The lack of outcome measures that are validated for use on children limits the effectiveness and generalizability of paediatric health care interventions. Statistical epidemiology is a broad concept encompassing a wide range of useful techniques for use in child health outcome assessment and development. However, the range of techniques that are available is often confusing and prohibits their adoption. In the paper an overview of methodology is provided within the paediatric context. It is demonstrated that in many cases assessment can be performed relatively straightforwardly by using standard statistical techniques, although sometimes more sophisticated techniques are required. Examples of both physiological and questionnaire-based outcomes are given. The usefulness of these techniques is highlighted for achieving specific objectives and ultimately for achieving methodological rigour in clinical outcome studies that are performed in the paediatric population. [source] Regular Tracheostomy Tube Changes to Prevent Formation of Granulation TissueTHE LARYNGOSCOPE, Issue 1 2003Kathleen Yaremchuk MD Abstract Objectives/Hypothesis Tracheostomy is a commonly performed operative procedure that has been described since 2000 b.c. The early indications for tracheostomy were for upper airway obstruction, usually occurring in young people as a result of an infectious process. Recently, tracheostomies are more commonly performed in the critically ill patient to assist in long-term ventilatory support. Granulation tissue at the stoma and the trachea has been described as a late complication resulting in bleeding, drainage, and difficulty with maintaining mechanical ventilatory support. Study Design The present report is of an observational study of a newly implemented policy that required regular changing of tracheostomy tubes. Comparable groups of patients were compared before and after this procedural change to document complications. Data collection consisted of chart reviews of all admissions for 1 year before the policy change and the subsequent 2 years. Complication rates were compared using standard statistical techniques. Methods A policy change was instituted that required all tracheostomy tubes to be changed every 2 weeks in conjunction with a detailed evaluation of the tracheostomy stoma. Charts were reviewed the year before the change in policy and in the subsequent 2 years to determine the incidence of granulation tissue requiring operative intervention. Results The number of patients requiring surgical intervention secondary to granulation tissue showed a statistically significant decrease (P = .02). A review of policies and procedures from the six largest hospitals in southeastern Michigan had no recommendations for routine tracheostomy tube changes. Conclusions A policy requiring a routine change of tracheostomy tubes results in fewer complications from granulation tissue. Tracheostomy tube changes to prevent granulation tissue and its complications. [source] | |||||||||||||