The Development of the CAT Statistical Injury Severity Score Incorporating Comorbidities, Age, and TRISS Open Access

Rutkowski, Rachel Elizabeth (2012)

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The Development of the CAT Statistical Injury Severity Score Incorporating Comorbidities, Age, and TRISS

Background: Trauma severity scoring is a tool that standardizes the risk of a certain outcome, such as death, following a trauma incident. A universal, quantitative representation of this risk is critical to clinical treatment evaluation and the advancement of trauma research. The triage of patients, the assessment of hospital and clinic care, the prediction of trauma patient outcome performance, and epidemiologic studies all rely on trauma severity scoring. Despite the many advancements and promising applications of new severity scores, there is still a need for acceptance of these valuable tools by clinicians. There is a strong push for the statistical models to better account for comorbid conditions. Often, age is used as a proxy to represent the effect of pre-existing conditions as it is believed that many conditions like heart disease worsen or develop later in life. However, such logic does not always apply to all conditions or patients.

Methods: A sample of 1,250,549 patients and 39 variables was taken from the National Trauma Data Bank Version 7.1 between the Emergency Department admission years 2002 to 2006. Logistic Regression, multiple imputation, and model discrimination techniques (NRI/IDI) were employed to investigate the relationship between comorbidities, TRISS, and age through model development. Mortality risk ratios from model building analysis were used to create two Comorbidity-Age-TRISS (CAT) scores. Comparisons between the CAT models, the unadjusted comorbidity model, and binary comorbidity model with TRISS and age were conducted.

Results: All models show a significant increased risk in mortality for a patient with pre-existing conditions; however, the score models show the highest risk - unadjusted model: RR=1.018, 95% CI=(1.018, 1.019); binary model: RR=1.018, 95% CI= (1.018, 1.019), unaltered CAT model: RR=1.273, 95% CI= (1.264, 1.283), beneficial CAT model: RR=1.185, 95% CI= (1.177, 1.192).

Conclusions: Comorbidities play a major role in the development of mortality risk. However, the extent to which these comorbidities affect mortality is still unclear. More research needs to be conducted on the conditions producing beneficial risk ratios (RR<1), and a unified approach to dealing with them in the creation of the scores should be employed.

Table of Contents

Table of Contents
Chapter One: Introduction...1

Problem Statement...2
Purpose Statement...3
Significance Statement...5

Chapter Two: Review of Literature...7

Review of Anatomic Scores...7
Review of Physiologic Status Scores...12
Review of Comorbidity Adjustment Scores...12
Review of Combined Scoring Systems...13

Chapter Three: Research Methodology...15

Description of the Procedures...15

Data Cleaning & Variable Manipulations...15
Methods for Data Investigation: Descriptive Statistics...34
Methods for Data Investigation: Regression Analysis...36
CAT Severity Score Creation and Testing...43

Rationale for Solution Choice...47

Chapter Four: Results...50

Description of the Outcome Results...50

Results of Data Investigation: Descriptive Statistics...50
Results of Data Investigation: Regression Analysis...85
CAT Severity Score Testing Results...102

Unexpected Problems and Findings...105

Chapter Five: Conclusions, Implications, and Recommendations...108


Appendix A: SAS Code...115

Analysis Part 1...115
Analysis Part 2...117
Analysis Part 3...119
Analysis Part 4...128
Analysis Part 5...129
Analysis Part 6...131
Analysis Part 7...221
Analysis Part 8...240

Appendix B: SAS Macro...249

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