Topics in Bayesian sample size determination and Bayesian model selection.

Includes bibliographical references (p. 84-87).This dissertation contains three topics using the Bayesian paradigm for statistical inference. The first topic is related to Bayesian sample size determination with a misclassified prevalence variable when two possibly dependent diagnostic tests are used for estimation. After accounting for the dependence structure, the required sample size will be larger than that assuming independence between the tests. The second topic is also concerned with Bayesian sample size calculation with a misclassified binary response variable. Differing from the first topic, an error-free covariate is added. Simulations demonstrate that choices of prior distributions have a great impact on the resultant sample size. The last topic is about Bayesian variable selection under the multiple regression model. Two competing Bayesian methods are Bayesian model averaging and reversible jump MCMC. It is found that reversible jump MCMC, expected to give better models, does not seem to differ from Bayesian model averaging in examples considered.by Dunlei Cheng.Ph.D

A Bayesian approach to sample size determination for studies designed to evaluate continuous medical tests

We develop a Bayesian approach to sample size and power calculations for cross-sectional studies that are designed to evaluate and compare continuous medical tests. For studies that involve one test or two conditionally independent or dependent tests, we present methods that are applicable when the true disease status of sampled individuals will be available and when it will not. Within a hypothesis testing framework, we consider the goal of demonstrating that a medical test has area under the receiver operating characteristic (ROC) curve that exceeds a minimum acceptable level or another relevant threshold, and the goals of establishing the superiority or equivalence of one test relative to another. A Bayesian average power criterion is used to determine a sample size that will yield high posterior probability, on average, of a future study correctly deciding in favor of these goals. The impacts on Bayesian average power of prior distributions, the proportion of diseased subjects in the study, and correlation among tests are investigated through simulation. The computational algorithm we develop involves simulating multiple data sets that are fit with Bayesian models using Gibbs sampling, and is executed by using WinBUGS in tandem with R.

Resource utilization and treatment costs of patients with severe hemophilia A: Real‐world data from the ATHNdataset

Abstract Hemophilia A is characterized by unpredictable spontaneous bleeds and chronic comorbidities. However, limited data exists at the national level into detailed management patterns related to patient clinical characteristics, representative real‐world dosing and treatment frequency, and costs. To assess and characterize the US severe hemophilia A (SHA) population, including subgroups of patients, in terms of clinical and demographic characteristics, healthcare resource utilization received at hemophilia treatment centers (HTCs), and projected annual costs of treatment utilizing data from the ATHNdataset of the American Thrombosis and Hemostasis Network (ATHN). Adult male people with SHA (PwSHA) (FVIII < 1%) were identified in the ATHNdataset between January 2013 and September 2019. This retrospective cohort study described patients’ demographic and clinical characteristics, clinical history, as well as the HTC‐related health resource utilization (HRU), treatment utilization, and projected annual treatment costs of US PwSHA received over the most recent year. Results are reported for the overall population and for three mutually exclusive subpopulations of patients: PwSHA with a history of and/or current inhibitors, PwSHA without a history of inhibitors but with (or a history of) one or more transfusion‐transmitted infections (hepatitis B virus [HBV], hepatitis C virus [HCV], or human immunodeficiency virus [HIV]), and PwSHA without a history of inhibitors or of transfusion‐transmitted infections (HBV, HCV, or HIV). Of the overall PwSHA cohort (N = 3677), there was a high prevalence of HCV (24.1%) and HIV (13.7%), while the prevalence of HBV (4.9%) was lower. Note that 20.5% of PwSHA overall currently or ever had FVIII inhibitors. On average, PwSHA had 2.8 total HTC visits per year, including 0.9 comprehensive care visits, 1.1 telephone contact visits, 0.5 office visits, and 0.1 surgeries or other procedures. However, 23.3% of PwSHA were not seen at an HTC, and 33.8% of PwSHA did not have a comprehensive care visit during their most recent year of data. HTC‐related HRU was similar between the overall cohort and across the patient subpopulations, although PwSHA and inhibitors had more frequent HTC visits (a mean of 3.6 visits annually vs. 2.5–2.8 in the other groups). Using reported treatment frequency and dosing, estimated mean annual hemophilia treatment costs varied by treatment and across the three subpopulations: extended half‐life factor product ($893,609–934,301 by subpopulation), standard half‐life factor product ($798,700–930,812), plasma‐derived factor product ($613,220–801,061), and non‐factor product treatment ($765,289—833,240). This study summarized recent sociodemographic and clinical characteristics, HTC‐related HRU, and HA treatments and projected costs among adult PwSHA, including among key subpopulations of PwSHA. PwSHA experience substantial clinical and resource burden on a chronic basis, despite the care coordination efforts of ATHN‐affiliated HTCs. These findings motivate further exploration of the drivers of resource utilization, observed differences across subpopulations and other disparities, and ongoing monitoring of clinical and treatment burden in the face of an evolving care landscape

Characterizing the Use of Direct Oral Anticoagulants in Children Using the American Thrombosis and Hemostasis Network Dataset (ATHNdataset)

Background: The incidence of venous thromboembolism (VTE) in children has risen significantly. (Raffini, Huang et al. 2009) There are currently four direct oral anticoagulants (DOACs) - apixaban, dabigatran, edoxaban, and rivaroxaban - approved for the acute treatment and prevention of VTE in adults. Advantages of these medications over the traditionally used anticoagulants, enoxaparin and warfarin, include fixed dosing, no need for routine laboratory monitoring, few drug interactions and no dietary restrictions. Despite lack of information on the safety and efficacy of these agents in children, pediatric hematologists across the United States are using DOACs in their patients based on extrapolated data from adult studies. The American Thrombosis and Hemostasis Network (ATHN) is a nonprofit network of over 140 federally funded Hemophilia Treatment Centers (HTCs) which provides the infrastructure for clinical and surveillance-based research. ATHN maintains the ATHNdataset (ADS), a "limited dataset" free of protected health information, with data collected on patients with bleeding and clotting disorders at participating HTCs within the Human Resources and Services Administration (HRSA)-supported regional hemophilia networks across the US. The authors acknowledge ATHN, the ATHN-affiliated U. S. Hemophilia Treatment Centers and their 39,000+ patients who have contributed their demographic, clinical, and genetic information to the ATHNdataset. Methods: The objective of this study was to describe the characteristics of pediatric patients diagnosed with VTE in the ADS, focusing on those patients who received a DOAC. Data were abstracted for patients in the ADS who had acute VTE at age <21 years from January 2010 to March 2019. Data extraction included basic demographics and information about VTE and treatment. Results : A total of 1,094 pediatric VTE cases were captured in the ADS. 577 (52.7%) were male. Caucasians were the most prevalent racial group (n = 809; 74%), followed by African-Americans (n = 203; 18.6%).14.9% (n = 163) were Hispanic. Deep venous thrombosis (DVT) was the most prevalent pediatric VTE reported in the ADS (n=889, 81.3%), followed by pulmonary embolism and cerebral venous thrombosis (n=130, 11.9% and n=40, 3.7% respectively). VTE location by age group is listed in Table 1. The most common DVT location was the lower extremities or pelvis, comprising 37.5% (n = 333) of all reported DVTs. Upper extremities or upper thorax DVT occurred less often (n = 211; 23.8 %). 345 (38.8 %) cases were reported only as "DVT" without a specific thrombus location. We reviewed 1,051 anticoagulant prescriptions for 650 VTE patients (mean 1.6 prescriptions per person). Enoxaparin was the most commonly prescribed anticoagulant (n = 676 prescriptions; 64.3%) followed by warfarin (n = 178 prescriptions, 16.9%). Interestingly, 116 (11%) patients, from 21 HTCs, had a DOAC prescribed as their anticoagulant regimen. Anticoagulant prescription by anticoagulant starting age is shown in Table 2. Further analysis of the DOAC subgroup showed that rivaroxaban was the most prescribed DOAC with 77.6% (n = 90/116) of the patients using this agent. Apixaban and dabigatran use was also reported (n= 23, 19.8% and n= 3, 2.6% respectively). The majority of DOACs were prescribed for patients older than 13 years of (111/116, 95.7 %). In children between 3 to 6 years of age (n = 3), rivaroxaban was the only DOAC prescribed. DOACs were primarily used to treat DVT of the extremities (84/116 patients). Other scenarios in which DOACs were also prescribed were PE and abdominal venous thrombosis patients (26, and 4 patients, respectively). Anticoagulant prescription by anticoagulant starting age is shown in Table 2. Conclusion: DVT of the lower extremities and pelvis is the most prevalent pediatric VTE in the ADS. Enoxaparin and warfarin remain the main anticoagulant agents used for pediatric VTE treatment. Despite lack of an FDA-approved pediatric indication, hematologists in US-based HTCs are already using DOACs in pediatric patients with VTE. As further characterization of DOAC use in children is needed, the authors, in collaboration with ATHN, are currently building a multi-institutional retrospective and prospective registry, ATHN 15. This registry will serve as a resource for pediatric hematologists to collect real-world use of DOACs in children, as we await the results of prospective clinical trials. Disclosures Davila: Octapharma: Other: Grant to attend VWD meeting ; Genentech: Other: Advisory board; Spire Learning: Speakers Bureau. Raffini:Bayer: Other: Advisory Board; CSL Behring: Other: Advisory Board; Roche: Other: Advisory Board. Thornburg:Sanofi Genzyme: Research Funding; Bluebird bio: Other: Data Safety Monitoring Board; Genentech: Speakers Bureau; NovoNordisk: Research Funding; Ironwood: Other: Data Safety Monitoring Board; Sanofi Genzyme: Other: Data Safety Monitoring Board. Corrales-Medina:Octapharma: Membership on an entity's Board of Directors or advisory committees; Kedrion: Membership on an entity's Board of Directors or advisory committees; Bayer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda-Shire: Membership on an entity's Board of Directors or advisory committees, Research Funding

Athn 15: Characterizing the Real-World Use of Direct Oral Anticoagulants in Pediatric Patients - Interim Analysis

Background: There are currently four direct oral anticoagulants (DOACs) approved for the acute treatment and prevention of venous thromboembolism (VTE) in adults. Pediatric hematologists across the United States (US) are using DOACs for their patients based on extrapolated data from adult studies and recently published phase 3 pediatric-specific studies. (Brandao LR, et al. Blood, 2019 and Male C, et al. Lancet Haematol, 2020.) Because further data regarding DOAC use in children are needed, ATHN 15: Characterizing the Real-World Use of Direct Oral Anticoagulants in Pediatric Patients, was developed and is being sponsored by the American Thrombosis and Hemostasis Network (ATHN). The study is being conducted at ATHN-affiliated sites in the US and aims to characterize the real-world use of DOACs in children diagnosed with VTE. ATHN is a nonprofit network of over 140 federally funded hemophilia treatment centers (HTCs) that provides the infrastructure for clinical research and public health surveillance. Methods: Data being captured includes demographics, clinical characteristics, anticoagulation management, and treatment outcomes (bleeding and recurrent thrombosis) of patients <21 years of age, who have received or are receiving a DOAC since January 1, 2015 for the treatment of an acute VTE episode or prevention of thrombosis recurrence. Data are collected for up to 6 months from the start of DOAC treatment. Results: As of May 31, 2020, 76 patients from 9 sites have been enrolled (see Table 1 for demographics). Deep venous thrombosis (DVT) of the lower extremities or pelvis is the most prevalent VTE (n = 23, 30.26%), followed by DVT of the upper extremity or upper thorax and pulmonary embolism plus VTE (n = 22, 28.95 and n = 13, 17.1% respectively). 82.89% of patients did not have a history of prior VTE at the time of enrollment. Of the 15 patients with a radiologically confirmed anatomic anomaly, Paget Schroetter/Thoracic Outlet Syndrome and May-Turner Syndrome are the most common (n = 6, 40% and n = 4, 26.7%, respectively). Factor V Leiden heterozygosity, reported in 8 patients, is the most prevalent inherited thrombophilia. Forty-eight patients were identified as having a medical risk factor associated with their VTEs. Sixteen (33.3%) were classified as obese and another 13 (27.1%) had a hospital admission stay greater than 7 days and within 30 days prior to the VTE. At least one specific drug or environmental risk factor was reported in 44 patients. Concomitant use of hormonal contraception (currently taking/stopped within 4 weeks prior to VTE) and the presence of a central venous catheter (present at time of VTE or within 30 days prior to VTE) were the most commonly reported (n = 18, 40.9% and n = 15, 34.09%, respectively). Rivaroxaban is the most prescribed DOAC with 59.2% (n = 45) of patients using this agent. Apixaban and dabigatran use is also reported (n = 29; 38.2% and n = 2; 2.6% respectively). Of the 76 patients, 65 received a different anticoagulant prior to starting a DOAC. Enoxaparin and unfractionated heparin are most commonly prescribed prior to the institution of a DOAC regimen (n = 52, 80% and n = 17, 26.2%). Conclusions: Despite lack of an FDA-approved pediatric indication, hematologists in the US are already using DOACs for children with VTE. Most pediatric patients treated with a DOAC are older than 13 years of age, although we anticipate this will change as providers develop more comfort with these drugs. Interestingly, most of these patients were started on a different anticoagulation regimen prior to starting a DOAC. As enrollment continues, ATHN 15 will serve as a resource for pediatric hematologists to characterize the real-world use of DOACs in children. Further analysis will evaluate DOAC-specific utilization, efficacy and adverse events, including heavy menstrual bleeding. Disclosures Davila: Spire Learning: Speakers Bureau; ATHN: Other: Grant Funding. Corrales-Medina:Bayer: Consultancy; Takeda: Consultancy; Octapharma: Consultancy, Speakers Bureau. Raffini:XaTek: Other: Advisory Board; CSL Behring: Other: Advisory Board; HemaBiologics: Other: Advisory Board; Bayer: Other: Advisory Board; Roche: Other: Advisory Board. Thornburg:Sanofi Genzyme: Consultancy, Other: Data Safety Monitoring Board, Research Funding; NovoNordisk: Research Funding; Genentech: Speakers Bureau; Biomarin: Consultancy, Speakers Bureau; Bayer Pharmaceuticals: Research Funding; American Thrombosis and Hemostasis Network: Research Funding; National Hemophilia Foundation: Membership on an entity's Board of Directors or advisory committees, Research Funding; Ironwood Pharmaceuticals: Consultancy, Other: Data Safety Monitoring Board; Bluebird Bio: Consultancy; Spark Therapeutics: Consultancy. OffLabel Disclosure: Apixaban, Rivaroxaban, Dabigatran and Enoxaparin use in the pediatric population