title: A comparison of stroke severity proxy measures for claims data research: a population-based cohort study.
abstract: OBJECTIVE
  Confounding by disease severity has been viewed as an intractable problem in claims-based studies. A novel 7-variable stroke severity index (SSI) was designed for estimating stroke severity by using claims data. This study compared the performance of mortality models with various proxy measures of stroke severity, including the SSI, in patients hospitalized for acute ischemic stroke (AIS).
  
  
  METHODS
  Data from the Taiwan National Health Insurance Research Database (NHIRD) were analyzed. Three proxy measures of stroke severity were evaluated: Measure 1, the SSI; Measure 2, intensive care unit admission and length of stay; and Measure 3, surgical operation, mechanical ventilation, hemiplegia or hemiparesis, and residual neurological deficits. We performed logistic regression by including age, sex, vascular risk factors, Charlson comorbidity index, and one of the proxy measures as covariates to predict 30-day and 1-year mortality after AIS. Model discrimination was evaluated using the area under the receiver-operating characteristic curve (AUC).
  
  
  RESULTS
  We identified 7551 adult patients with AIS. Models using the SSI (Measure 1) outperformed models using the other proxy measures in predicting 30-day mortality (AUC 0.892 vs 0.851, p < 0.001 for Measure 2; 0.892 vs 0.853, p < 0.001 for Measure 3) and 1-year mortality (AUC 0.816 vs 0.784, p < 0.001 for Measure 2; 0.816 vs 0.782, p < 0.001 for Measure 3).
  
  
  CONCLUSIONS
  Using the SSI facilitated risk adjustment for stroke severity in mortality models for patients with AIS. The SSI is a viable methodological tool for stroke outcome studies using the NHIRD.
authors.affiliation: Division of Neurology, Department of Internal Medicine, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi City, Taiwan.
authors.forename: Sheng-Feng
authors.initials: SF
authors.lastname: Sung
authors.affiliation: Department of Medical Research, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chiayi City, Taiwan.
authors.forename: Solomon Chih-Cheng
authors.initials: SC
authors.lastname: Chen
authors.affiliation: Department of Neurology, Tainan Sin Lau Hospital, Tainan City, Taiwan.
authors.forename: Cheng-Yang
authors.initials: CY
authors.lastname: Hsieh
authors.affiliation: Department of Public Health, College of Medicine, National Cheng Kung University, Tainan City, Taiwan.
authors.forename: Chung-Yi
authors.initials: CY
authors.lastname: Li
authors.affiliation: Institute of Clinical Pharmacy and Pharmaceutical Sciences, College of Medicine, National Cheng Kung University, Tainan City, Taiwan.|Duke Clinical Research Institute, Duke University School of Medicine, Durham, NC, USA.
authors.forename: Edward Chia-Cheng
authors.initials: EC
authors.lastname: Lai
authors.affiliation: Department of Information Management and Institute of Healthcare Information Management, National Chung Cheng University, Chiayi County, Taiwan.
authors.forename: Ya-Han
authors.initials: YH
authors.lastname: Hu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002545:Brain Ischemia / Q000401:mortality / Q000503:physiopathology*; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D016208:Databases, Factual / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D012372:ROC Curve; D012307:Risk Factors; D012720:Severity of Illness Index; D020521:Stroke / Q000401:mortality / Q000503:physiopathology*; D013624:Taiwan; D013997:Time Factors
keywords: acute ischemic stroke; claims data; disease severity; outcomes research; pharmacoepidemiology