title: Analysis of multivariate longitudinal kidney function outcomes using generalized linear mixed models.
abstract: BACKGROUND
  Renal transplant patients are mandated to have continuous assessment of their kidney function over time to monitor disease progression determined by changes in blood urea nitrogen (BUN), serum creatinine (Cr), and estimated glomerular filtration rate (eGFR). Multivariate analysis of these outcomes that aims at identifying the differential factors that affect disease progression is of great clinical significance. Thus our study aims at demonstrating the application of different joint modeling approaches with random coefficients on a cohort of renal transplant patients and presenting a comparison of their performance through a pseudo-simulation study. The objective of this comparison is to identify the model with best performance and to determine whether accuracy compensates for complexity in the different multivariate joint models.
  
  
  RESULTS
  We propose a novel application of multivariate Generalized Linear Mixed Models (mGLMM) to analyze multiple longitudinal kidney function outcomes collected over 3 years on a cohort of 110 renal transplantation patients. The correlated outcomes BUN, Cr, and eGFR and the effect of various covariates such patient's gender, age and race on these markers was determined holistically using different mGLMMs. The performance of the various mGLMMs that encompass shared random intercept (SHRI), shared random intercept and slope (SHRIS), separate random intercept (SPRI) and separate random intercept and slope (SPRIS) was assessed to identify the one that has the best fit and most accurate estimates. A bootstrap pseudo-simulation study was conducted to gauge the tradeoff between the complexity and accuracy of the models. Accuracy was determined using two measures; the mean of the differences between the estimates of the bootstrapped datasets and the true beta obtained from the application of each model on the renal dataset, and the mean of the square of these differences. The results showed that SPRI provided most accurate estimates and did not exhibit any computational or convergence problem.
  
  
  CONCLUSIONS
  Higher accuracy was demonstrated when the level of complexity increased from shared random coefficient models to the separate random coefficient alternatives with SPRI showing to have the best fit and most accurate estimates.
authors.affiliation: Epidemiology and Population Health Department, Faculty of Health Sciences, American University of Beirut, P.O. Box 11-0236, Riad El-Solh, Beirut, 1107 2020, Lebanon. ms148@aub.edu.lb.
authors.forename: Miran A
authors.initials: MA
authors.lastname: Jaffa
authors.affiliation: Department of Public Health Sciences, Medical University of South Carolina, Charleston, SC, 29425, USA. gebregz@musc.edu.
authors.forename: Mulugeta
authors.initials: M
authors.lastname: Gebregziabher
authors.affiliation: Department of Medicine, Medical University of South Carolina, Charleston, SC, USA. Jaffaa@musc.edu.|Department of Biochemistry and Molecular Genetics, Faculty of Medicine, American University of Beirut, P.O. Box 11-0236, Riad El-Solh, Beirut, 1107 2020, Lebanon. Jaffaa@musc.edu.
authors.forename: Ayad A
authors.initials: AA
authors.lastname: Jaffa
mesh_terms: D003198:Computer Simulation; D005260:Female; D006801:Humans; D007668:Kidney / Q000503:physiopathology*; D007677:Kidney Function Tests; D016030:Kidney Transplantation; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D015999:Multivariate Analysis