Boyd, K. L. and Hutton, Jane L. (2006) Missing covariate data in parametric survival analysis : modelling the missing data mechanism. Working Paper. University of Warwick. Centre for Research in Statistical Methodology, Coventry.

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Abstract

Aims and Motivation To examine the effect of level of disability on the survival of children with cerebral palsy using a cohort taken from Bristol. The data is subject to, possibly not missing at random (NMAR), unobserved covariate data. Methods A joint survival model for the log-survival times and missing data mechanism is introduced. This approach enables us to model the missing data mechanism. This is then used to model the effect of level of ambulatory disability on survival in the cerebral palsy data. Extensions to the model are discussed to include continuous and multiple covariates. Results Analysis suggests that the effect of severe ambulation on survival in individuals with cerebral palsy is underestimated if no account is taken of the missing data mechanism. Simulations show that this model, under various distribution assumptions, performs well in comparison to basic exclusion techniques. Conclusions It is very important to consider the mechanism behind any missing data when studying survival. Slight deviances from the less restrictive assumptions can effect parameter estimates in survival models. In our data, we see an increased effect of severe ambulation on survival in those with cerebral palsy. A severe level of ambulatory disability causes a decrease in survival.

Item Type:	Working or Discussion Paper (Working Paper)
Subjects:	Q Science > QA Mathematics
Divisions:	Faculty of Science > Statistics
Library of Congress Subject Headings (LCSH):	Missing observations (Statistics), Survival analysis (Biometry), Cerebral palsy -- Mathematical models
Series Name:	Working papers
Publisher:	University of Warwick. Centre for Research in Statistical Methodology
Place of Publication:	Coventry
Date:	2006
Volume:	Vol.2006
Number:	No.2
Number of Pages:	25
Status:	Not Peer Reviewed
Access rights to Published version:	Open Access
References:	Collett, D. (1999), Modelling Survival Data in Medical Research, Chapman & Hall / CRC, London. Copas, J. & Shi, J. (2001), `A sensitivity analysis for publicatin bias in systematic reviews', Statistical Methods in Medical Research 10, 251{265. Cox, D. (1966), Festschrift for J. Neyman - Research Papers in Statistics, Wiley, chap- ter 4, pp. 55{71. Cox, D. (1972), `Regression models and life tables', Journal of the Royal Statistical Society, B 34, 187{220. Faires, D. & Burden, R. (2003), Numerical methods, 3 edn, Brooks/Cole, chapter 4. Hemming, K., Hutton, J. & Pharoah, P. (2006), `Long-term survival for a cohort of adults with cerebral palsy', Developmental Medicine and Child Neurology 48, 90{5. Herring, A. & Ibrahim, J. (2001), `Likelihood-based methods for missing covariates in the cox proportional hazards model', Journal of the American Statistical Association 96, 292{302. Hutton, J., Cooke, T. & Pharoah, P. (1994), `Life expectancy in children with cerebral palsy', British Medical Journal 309, 431{5. Hutton, J. & Monaghan, P. (2002), `Choice of parametric accelerated life and propor- tional hazards models for survival data: Asymptotic results', Lifetime Data Analysis 8, 375{393. Hutton, J. & Pharoah, P. (2002), `E®ects of cognitive, motor, and sensory disabilities on survival in cerebral palsy', Archives of Disease in Childhood 86, 84{9. Ibrahim, J., Chen, M.-H. & Lipsitz, S. (1999), `Monte carlo em for missing covariates in parametric regression models', Biometrics 591-596, 55. Lipsitz, S. & Ibrahim, J. (1998), `Estimating equations with incomplete categorical co- variates in the cox model', Biometrics 54, 1002{13. Little, R. & Rubin, D. (2002), Statistical Analysis with Missing Data, John Wiley and Sons, Inc., New York. Meng, X. & Schenker, N. (1999), `Maximum likelihood estimation for linear regres- sion models with right censored outcomes and missing predictors', Computational Statistics and Data Analysis 29, 471{483. Woods, G. (1957), Cerebral Palsy in childhood: The aetiology and clinica assessment with particular reference to findings in Bristol, PhD thesis, University of Bristol, Bristol, UK.
URI:	http://wrap.warwick.ac.uk/id/eprint/35562

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