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Evaluating Comparative Effectiveness of Simultaneous Liver and Kidney Transplant versus Liver Transplant Alone using Instrumental Variables

Wang, Mengqi (2020) Evaluating Comparative Effectiveness of Simultaneous Liver and Kidney Transplant versus Liver Transplant Alone using Instrumental Variables. Master's Thesis, University of Pittsburgh. (Unpublished)

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Improving the quality of medical care often requires assessment of comparative effectiveness between treatments. Although randomized controlled trials (RCTs) are considered as the gold standard for generating evidence, they may not be feasible or ethical to conduct for some comparisons. Therefore, observational studies are required to address many research questions. However, observational data may lead to a high potential for selection bias because subjects or physicians choose their treatments, which may complicate the estimation of causal effects. As one approach to overcome these issues, instrumental variables (IVs) can be used to potentially estimate unbiased causal effect in the setting of observational comparative effectiveness research.
The goal of this thesis is reducing unmeasured confounding in an observational study to compare the effectiveness of simultaneous liver and kidney transplants (SLKT) versus liver-only transplants (LTA) in patients who were on the liver transplant wait list with dialysis. We hypothesize that SLKT could lower mortality by replacing both organs in the same operation.
A two-stage least squares (2SLS) was used to estimate causal effects. The first stage was regressing treatment on IV and covariates to determine whether IV met the assumption of strongly predicting treatment. Then, the second stage least squares analysis was performed by regressing outcome on estimated treatment and covariates. This analysis used several strategies for formulating the IV based on geographic region, with similar results. Although our IV met the necessary assumptions, results did not show a significant causal relationship between treatment and mortality.
Findings of this thesis are significant to public health because more than ten thousand patients in the US are on the liver transplant waiting list. While performing both a kidney and liver transplant in these patients may save lives, we are not aware of any other studies that evaluated this problem using IVs or other approaches that potentially account for unmeasured confounding. By evaluating the causal effects of the different transplant approaches, physician and patients can make more informed decision. The information may also be important for organ allocation strategies nationally.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Wang, Mengqimew173@pitt.edumew173
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairLandsittel,
Committee MemberYouk,
Committee MemberBuchanich,
Committee MemberCarlson,
Date: 31 March 2020
Date Type: Completion
Defense Date: 20 April 2020
Approval Date: 31 July 2020
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 57
Institution: University of Pittsburgh
Schools and Programs: School of Public Health > Biostatistics
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: kidney transplant; liver transplant; instrumental variables
Date Deposited: 30 Jul 2020 21:05
Last Modified: 31 Jul 2020 14:02


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