title: A new comorbidity index: the health-related quality of life comorbidity index.
abstract: OBJECTIVE
  To derive and validate the health-related quality of life comorbidity index (HRQL-CI).
  
  
  METHODS
  Of 261 clinical classification codes (CCCs) in the 2003 Medical Expenditure Panel Survey (MEPS), 44 were identified as adult, gender-neutral, chronic conditions. The least absolute shrinkage and selection operator (LASSO) procedure identified CCCs significantly associated with the Short Form-12 physical component summary (PCS) and mental component summary (MCS) scores. Regression models were fitted with the selected CCCs, resulting in two subsets corresponding to PCS and MCS, collectively called the HRQL-CI. Internal validation was assessed using 10-fold cross-validation, whereas external validation in terms of prediction accuracy was assessed in the 2005 MEPS database. Prediction errors and model R² were compared between HRQL-CI models and models using the Charlson-CI.
  
  
  RESULTS
  LASSO identified 20 CCCs significantly associated with PCS and 15 with MCS. The R² for the models, including the HRQL-CI (0.28 for PCS and 0.16 for MCS) were greater than those using the Charlson-CI (0.13 for PCS and 0.01 for MCS). The same pattern of higher R² for models using the HRQL-CI was observed in the validation tests.
  
  
  CONCLUSIONS
  The HRQL-CI is a valid risk adjustment index, outperforming the Charlson-CI. Further work is needed to test its performance in other patient populations and measures of HRQL.
authors.affiliation: Department of Biostatistics, School of Public Health, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Bhramar
authors.initials: B
authors.lastname: Mukherjee
authors.forename: Huang-Tz
authors.initials: HT
authors.lastname: Ou
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.forename: Steven R
authors.initials: SR
authors.lastname: Erickson
mesh_terms: D000328:Adult; D015897:Comorbidity; D006304:Health Status; D006801:Humans; D011788:Quality of Life; D018570:Risk Assessment; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires / Q000592:standards*