Bias and Sensitivity Analysis When Estimating Treatment Effects from the Cox Model with Omitted Covariates

Omission of relevant covariates can lead to bias when estimating treatment or exposure effects from survival data in both randomized controlled trials and observational studies. This paper presents a general approach to assessing bias when covariates are omitted from the Cox model. The proposed method is applicable to both randomized and non‐randomized studies. We distinguish between the effects of three possible sources of bias: omission of a balanced covariate, data censoring and unmeasured confounding. Asymptotic formulae for determining the bias are derived from the large sample properties of the maximum likelihood estimator. A simulation study is used to demonstrate the validity of the bias formulae and to characterize the influence of the different sources of bias. It is shown that the bias converges to fixed limits as the effect of the omitted covariate increases, irrespective of the degree of confounding. The bias formulae are used as the basis for developing a new method of sensitivity analysis to assess the impact of omitted covariates on estimates of treatment or exposure effects. In simulation studies, the proposed method gave unbiased treatment estimates and confidence intervals with good coverage when the true sensitivity parameters were known. We describe application of the method to a randomized controlled trial and a non‐randomized study

SLO Botanical Garden - Greenhouse Propagation Tables

This paper describes the planning and construction involved in retrofitting the San Luis Obispo Botanical Garden propagation greenhouse. When trying to determine a senior project, the author of this paper met with multiple non-profit organizations. After interviewing with them, the author determined that the San Luis Obispo Botanical Garden was the organization he wanted to work with. After meeting with the facility director, Chenda Lor, many potential projects were identified but the organization determined this would be of the most use immediately. Upon selection, the scope of work was determined as helping refurbish the propagation greenhouse by removal and/or demolition of the tables in the existing facility as well as the installation of new propagation tables. This paper will explain in detail the planning, financing, and construction phases of the project. The author along with several peer volunteers completed this project over a 3-month period. Planning and financing of this project occurred during March and April of 2020 and Construction began in May 2020. The final product was delivered to the San Luis Obispo Botanical Garden propagation team on June 2nd, 2020

Statistical aspects of credit scoring

This thesis is concerned with statistical aspects of credit scoring, the process of determining how likely an applicant for credit is to default with repayments. In Chapters 1-4 a detailed introduction to credit scoring methodology is presented, including evaluation of previous published work on credit scoring and a review of discrimination and classification techniques. In Chapter 5 we describe different approaches to measuring the absolute and relative performance of credit scoring models. Two significance tests are proposed for comparing the bad rate amongst the accepts (or the error rate) from two classifiers. In Chapter 6 we consider different approaches to reject inference, the procedure of allocating class membership probabilities to the rejects. One reason for needing reject inference is to reduce the sample selection bias that results from using a sample consisting only of accepted applicants to build new scorecards. We show that the characteristic vectors for the rejects do not contain information about the parameters of the observed data likelihood, unless extra information or assumptions are included. Methods of reject inference which incorporate additional information are proposed. In Chapter 7 we make comparisons of a range of different parametric and nonparametric classification techniques for credit scoring: linear regression, logistic regression, projection pursuit regression, Poisson regression, decision trees and decision graphs. We conclude that classifier performance is fairly insensitive to the particular technique adopted. In Chapter 8 we describe the application of the k-NN method to credit scoring. We propose using an adjusted version of the Eucidean distance metric, which is designed to incorporate knowledge of class separation contained in the data. We evaluate properties of the k-NN classifier through empirical studies and make comparisons with existing techniques

Effectiveness of intervention on physical activity of children: systematic review and meta-analysis of controlled trials with objectively measured outcomes (EarlyBird 54).

addresses: Department of Endocrinology and Metabolism, Peninsula College of Medicine and Dentistry, Plymouth University Campus, Plymouth, UK. [email protected]: Journal Article; Meta-Analysis; Research Support, Non-U.S. Gov't; ReviewCopyright © 2012 by the BMJ Publishing Group Ltd. This articles was first published in: BMJ, 2012, Vol. 345, pp. e5888 -To determine whether, and to what extent, physical activity interventions affect the overall activity levels of children

Liability for Marine Pollution from Offshore Operations

This paper addresses various aspects of liability for marine pollution arising from offshore operations. The myriad of provincial, federal and international instruments which are relevant to pollution in the offshore generates complex compliance and liability issues. An operator may be subject to both criminal and civil liability for pollution under several different legislative regimes. This paper is divided into two parts. First, compliance considerations are reviewed with the primary compliance requirements under the various acts and regulations applicable to offshore operations highlighted. In the second part, the extent of civil liability for marine pollution is examined

Which children and young people are excluded from school? Findings from the Avon Longitudinal Study of Parents and Children (ALSPAC) - poster abstract

Poster abstract presented at Spring Meeting for Clinician Scientists in Training 2015BACKGROUND: School exclusion is a disciplinary method used to remove a child from the school environment. It is known to affect certain groups disproportionately, including boys, some ethnic minorities, children in care, children in poverty, and children with special educational needs. Population-based studies on wider characteristics of excluded pupils are scarce. The aim of this study was to describe factors associated with school exclusion in the Avon Longitudinal Study of Parents and Children (ALSPAC), focussing on neurodevelopment and mental health. METHODS: ALSPAC is a prospective population-based British birth cohort study, with the initial sample consisting of 14 541 pregnancies. The study has data for whether a child has been permanently excluded from school up to the age of 8 years as reported by parents and also permanent and fixed period exclusions in the preceding 12 months as reported by parents and young people at age 16 years. Upstream risk factors were assessed for associations with exclusion on univariable analysis. The association with social communication difficulties was investigated with multivariable logistic regression. FINDINGS: Data for exclusions up to the age of 8 years were available for 8245 ALSPAC participants and 4482 participants for exclusion at age 16 years. 53 pupils (0·6%) were excluded from school by age 8 years, and 390 (8·7%) at age 16 years. The odds of exclusion by 8 years and at 16 years were increased with male sex (p=0·001 and p<0·0001, respectively), low family income (p=0·014 and p<0·0001), family adversity (p<0·0001 for both), maternal psychopathology (p=0·013 and p=0·004), low intelligence quotient (p=0·041 and p<0·0001), mental health difficulties (p<0·0001 for both), psychiatric disorder (p<0·0001 for both), social communication difficulties (p<0·0001 for both), antisocial activities (p=0·004 and p<0·0001), bullying or being bullied (p=0·005 and p<0·0001), low educational attainment (p<0·0001 for both), and increased special educational needs (p<0·0001 for both). On multivariable analysis, having social communication difficulties above a clinical threshold on the Social Communication Disorders Checklist was strongly associated with exclusion by 8 years (odds ratio 7·4, 95% CI 3·6-15·4) and at 16 years (2·3, 1·5-3·5), after adjustment for relevant confounders. INTERPRETATION: Although cohort attrition and small numbers of exclusions at 8 years are limitations, this study suggests that school exclusion is associated with numerous risk factors identifiable at or before primary school entry. Child health professionals have an important role in the holistic assessment of children who are excluded, or who are at risk of school exclusion. There is particular need to ensure that mental health and neurodevelopmental difficulties are appropriately recognised and supported. FUNDING: National Institute for Health Research Academic Clinical Fellowship

Association of urinary bisphenol a concentration with heart disease: evidence from NHANES 2003/06.

addresses: Epidemiology and Public Health Group, Peninsula Medical School, University of Exeter, Exeter, United Kingdom. [email protected]: PMCID: PMC2800195types: Journal Article; Research Support, Non-U.S. Gov'tCopyright: © 2010 Melzer et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Bisphenol A (BPA) is a high production volume chemical widely used in food and drinks packaging. Associations have previously been reported between urinary BPA concentrations and heart disease, diabetes and liver enzymes in adult participants of the National Health and Nutrition Examination Survey (NHANES) 2003/04. We aimed to estimate associations between urinary BPA concentrations and health measures in NHANES 2005/06 and in data pooled across collection years

Exploring the Adolescent Fall in Physical Activity: A 10-yr Cohort Study (EarlyBird 41)

This is a non-final version of an article published in final form in Medicine & Science in Sports & Exercise Vol. 47 (10), pp. 2084–2092 (2015)INTRODUCTION: Contemporary adolescents are deemed inactive, especially girls, but whether for biological reasons associated with their maturation, changes in their behavior or because of environmental constraints, is uncertain. We examined the trends in physical activity (PA) in relation to both biological and environmental factors in an attempt to establish what drives activity patterns from childhood through adolescence. METHODS: Physical activity (7-d Actigraph accelerometry) was measured annually from 5 to 15 yr in a single cohort of some 300 UK children. Total PA (TPA; in-school and out-of-school separately and combined as whole day) and intensity-specific PA (sedentary, light, and moderate-and-vigorous [MVPA]) were analyzed. Biological age (years before/after measured peak height velocity) and pubertal stage (self-reported pubic hair development-Tanner staging) were also measured as was socioeconomic status (postcode-derived index of multiple deprivation [IMD]). RESULTS: Total PA was stable from 5 to 8 yr (trend P = 0.10) but fell progressively from 9 to 15 yr (by approximately 30% in girls and approximately 20% in boys, both P < 0.001; sex interaction, P < 0.01). Half of this fall was attributable to light intensity PA and only a quarter to MVPA. The decline in PA was related similarly to chronological and biological age, whereas pubertal stage explained the more rapid PA decline in girls (puberty-adjusted sex interaction, P = 0.51). Total PA fell to the same extent for in-school and out-of-school settings (both P < 0.001), and for lower and higher IMD areas (both P < 0.001). Total PA tracked moderately to strongly from childhood into adolescence (r = 0.58; P < 0.001). CONCLUSIONS: The adolescent decline in PA is consistent across different environmental settings, attributable to falls in light-intensity/habitual activity and influenced by puberty, suggesting that the inactivity of adolescence may, in part, be under biological control.Bright Future TrustKirby Laing FoundationPeninsula FoundationEarlyBird Diabetes TrustNational Institute for Health Research (NIHR) Collaborations for Leadership in Applied Health Research and Care (CLAHRC

Variation in referral and access to new psychological therapy services by age: an empirical quantitative study.

Background: Older people with common mental health problems (CMHPs) are known to have reduced rates of referral to psychological therapy. Aim: We aimed to assess referral rates to the Improving Access to Psychological Therapies (IAPT) service, contact with a therapist and clinical outcome by age. Design and Setting: Empirical research using patient episodes of care from South West IAPT. Method: By analysing 82,513 episodes of care (2010-2011), referral rates and clinical improvement were compared to both total population and estimated prevalence in each age group using IAPT data. Probable recovery of those completing treatment were calculated for each group. Results: Estimated prevalence of CMHPs peaks in 45–49 year olds (20.59% of population). The proportions of patients identified with CMHPs being referred peaks at 20-24 years (22.95%) and reduces with increase in age thereafter to 6.00% for 70-74 year olds. Once referred, the proportion of those attending first treatment increases with age between 18 years (57.64%) and 64 years (76.97%). In addition, the percentage of those having a clinical improvement gradually increases from the age 20 years (12.94%) to 69 years (20.74%). Conclusion: Younger adults are more readily referred to IAPT services. However, as a proportion of those referred, probabilities of attending once, attending more than once, and clinical improvement, increase with age. It is uncertain whether optimum levels of referral have been reached for young adults. It is important to establish whether changes to service configuration, treatment options, and GP behaviour can increase referrals for middle-aged and older adults