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\begin{document}

\title{Personalizing Evidence for Shoulder Fracture Patients Using an Extended
Instrumental Variable Causal Forest Algorithm}



\author[1]{John M. Brooks}%
\author[2]{Cole G. Chapman}%
\author[3]{Sarah Floyd}%
\author[4]{Brian K. Chen}%
\author[5]{Charles A. Thigpen}%
\author[6]{Michael Kissenberth}%
\affil[1]{Center for Effectiveness Research in Orthopaedics - Arnold School of Public Health Greenville, South Carolina United States}%
\affil[2]{University of Iowa }%
\affil[3]{Clemson University College of Behavioral Social and Health Sciences}%
\affil[4]{University of South Carolina Arnold School of Public Health}%
\affil[5]{University of South Carolina}%
\affil[6]{Prisma Health}%


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  \date{June 14, 2024}


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\begin{abstract}
Objective: To assess the ability of an extended Instrumental Variable
Causal Forest Algorithm (IV-CFA) to provide personalized evidence of
early surgery effects on benefits and detriments for elderly shoulder
fracture patients. Data Sources/Study Setting: Population of 72,751
fee-for-service Medicare beneficiaries with proximal humerus fractures
(PHFs) in 2011 who survived a 60-day treatment window after an index PHF
and were continuously Medicare fee-for-service eligible over the period
12 months prior to index to the minimum of 12 months after index or
death. Study Design: IV-CFA estimated early surgery effects on both
beneficial and detrimental outcomes for each patient in the study
population. Classification and regression trees (CART) were applied to
these estimates to create patient reference classes. Two-stage least
squares (2SLS) estimators were applied to patients in each reference
class to scrutinize the estimates relative to the known 2SLS properties.
Principal Findings: This approach uncovered distinct reference classes
of elderly PHF patients with respect to early surgery effects on benefit
and detriment. Older, frailer patients with more comorbidities, and
lower utilizers of healthcare were less likely to gain benefit and more
likely to have detriment from early surgery. Reference classes were
characterized by the appropriateness of early surgery rates with respect
to benefit and detriment. Conclusions: Extended IV-CFA provides an
illuminating method to uncover reference classes of patients based on
treatment effects using observational data with a strong instrumental
variable. This study isolated reference classes of new PHF patients in
which changes in early surgery rates would improve patient outcomes. The
inability to measure fracture complexity in Medicare claims means
providers will need to discuss the appropriateness of these estimates to
patients within a reference class in context of this missing
information.%
\end{abstract}%



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