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Publication Detail
Combining fractional polynomial model building with multiple imputation
  • Publication Type:
    Journal article
  • Publication Sub Type:
  • Authors:
    Morris TP, White IR, Carpenter JR, Stanworth SJ, Royston P
  • Publisher:
    John Wiley and Sons
  • Publication date:
  • Journal:
    Statistics in Medicine
  • Status:
  • Print ISSN:
  • Keywords:
    fractional polynomials, multivariable fractional polynomials, multiple imputation, missing data
  • Addresses:
    London School of Hygiene and Tropical Medicine

    MRC Clinical Trials Unit at UCL

    MRC Biostatistics Unit

    NHS Blood and Transplant
Multivariable fractional polynomial (MFP) models are commonly used in medical research. The datasets in which MFP models are applied often contain covariates with missing values. To handle the missing values, we describe methods for combining multiple imputation with MFP modelling, considering in turn three issues: first, how to impute so that the imputation model does not favour certain fractional polynomial (FP) models over others; second, how to estimate the FP exponents in multiply imputed data; and third, how to choose between models of differing complexity. Two imputation methods are outlined for different settings. For model selection, methods based on Wald-type statistics and weighted likelihood-ratio tests are proposed and evaluated in simulation studies. The Wald-based method is very slightly better at estimating FP exponents. Type I error rates are very similar for both methods, although slightly less well controlled than analysis of complete records; however, there is potential for substantial gains in power over the analysis of complete records. We illustrate the two methods in a dataset from five trauma registries for which a prognostic model has previously been published, contrasting the selected models with that obtained by analysing the complete records only. © 2015 The Authors. Statistics in Medicine Published by John Wiley & Sons Ltd.
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