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HEOR leaders

Our health economics and outcomes research (HEOR) capabilities and expertise span several therapeutic areas. We invite you to learn more about our experts and see examples of our work.


Paul Dluzniewski, PhD

Paul Dluzniewski, PhD, joined Optum in October of 2021 as vice president of research for health economics and outcomes research (HEOR) where he leads our team of researchers conducting observational studies focused on clinical and economic value across multiple therapeutic areas. He has over 2 decades of research experience with nearly 10 years spent leading evidence generation activities in the biotechnology and pharmaceutical industry. Prior to joining Optum, Dluzniewski was a director at the Center for Observational Research at Amgen. As product area lead for the cardiovascular-metabolic group, he led a team of epidemiologists whose work focused on therapies used to treat patients at elevated risk of cardiovascular disease and other metabolic diseases. The team’s evidence generation efforts focused on conducting observational research to inform the benefit-risk profile of Amgen’s therapies and highlight the clinical value of both marketed and pipeline products. Before his time at Amgen, Dluzniewski worked as a senior research analyst at Health Net, a large California-based insurance company.

Residing on the West Coast, Dluzniewski currently serves as an adjunct assistant professor at the UCLA Fielding School of Public Health. He received his PhD in Epidemiology from the Johns Hopkins Bloomberg School of Public Health, where his research focused on prostate cancer, specifically examining methodological issues that impact the validity of genome-wide association studies. He received his Master of Public Health in Epidemiology from the Boston University School of Public Health and completed his undergraduate training at the Massachusetts Institute of Technology.


Passionate about providing high quality research solutions, Ami Buikema supports research design and innovation across all therapeutic areas. She earned her Master of Public Health in epidemiology from the University of Minnesota and is working towards her doctorate.

Buikema has authored and co-authored publications appearing in numerous journals, including Journal of the American Medical Association and Hepatology.

Selected published work

Buikema AR, Brekke L, Anderson A, Koep E, Van Voorhis D, Sharpsten L, Hahn B, Ray R, Stanford R. The effect of delaying initiation with umeclidinium/vilanterol in patients with COPD: an observational administrative claims database analysis using marginal structural models. Multidiscip Respir Med. 2018 Oct 11;13:38.

Rosenblatt L, Buikema AR, Seare J, Bengtson LG, Johnson J, Cao F, Villasis-Keever A. Economic outcomes of first-line regimen switching among stable patients with HIV. J Manag Care Spec Pharm. 2017 Jul;23(7):725-734.

Jain A, Marshall J, Buikema A, Bancroft T, Kelly JP, Newschaffer CJ. Autism occurrence by MMR vaccine status among US children with older siblings with and without autism. JAMA. 2015 Apr 21;313(15):1534-40.

Stanford RH, Buikema AR, Riedel AA, Camargo CA Jr, Rey GG, Chapman KR. Asthma controller delay and recurrence risk after an emergency department visit or hospitalization. Resp Med. 2012 Dec;106(12):1631-8.

Gordon SC, Pockros PJ, Terrault NA, Hoop RS, Buikema A, Nerenz D, Hamzeh FM. Impact of disease severity on healthcare costs in patients with chronic hepatitis C (CHC) virus infection. Hepatology. 2012 Nov; 56(5): 1651-60.


HEOR, Health Economics Outcomes Research, Health Economics, Epidemiology, Observational Research, Real-world Evidence, Real-world Data, Respiratory Disease, Infectious Disease, Vaccines

Benjamin Chastek joined Optum in 2004 and is the therapeutic lead for HEOR studies involving immunology. He oversees research, data acquisitions and study execution. 

Since 2008, he has focused on research related to rheumatoid arthritis, psoriasis, psoriatic arthritis and other autoimmune disorders.

Chastek has a Master of Science in statistics from Minnesota State University, where he specialized in theoretical and computational statistics. Prior to becoming a therapeutic lead, he was a researcher within Optum with a specific expertise on large claims datasets. 

Some of the areas in which he is well versed in include survival analysis, longitudinal or panel data sets, and cost analysis, including the presence of right censoring. 

His research has been presented at a number of national and international conferences and in numerous journals including the American College of Rheumatology and American Journal of Pharmacy Benefits.   

Published work

Majethia S, Lee I, Chastek B, Bunner S, Wolf J, Hsiao A, Mozaffari E. Economic impact of applying the AASLD-IDSA simplified treatment algorithm on the real-world management of hepatitis CJ Manag Care Spec Pharm, 2022 Jan;28(1):48-57.

Chastek B, Segal S, Bonafede RP, Watson C, Becker L, Chaudhari S, Harrison DJ, Gandra SR. Comparative Effectiveness of TNF Blockers in Rheumatoid Arthritis PatientsAm J Pharm Benefits. 2013;5(Special Issue):SP14-SP22. 

Chastek B, Kulakodlu M, Valluri S, Seal B. Impact of Metastatic Colorectal Cancer Stage and Number of Treatment Courses on Patient Health Care Costs and UtilizationPostgrad Med. 2013 Mar;125(2):73-82.

Chastek B, Harley C, Kallich J, Newcomer L, Paoli C, Teitelbaum A. Health Care Costs for Patients With Cancer at the End of LifeJ Oncol Pract. 2012 Nov;8(6):75s-80s.

Pollack M, Chastek B, Williams S, Moran JImpact of treatment complexity on adherence and glycemic control: An analysis of oral antidiabetic agentsJCOM. 2010 Jun; 17(6), 257-265.

Chastek BJ, Oleen-Burkey M, Lopez-Bresnahan MVMedical chart validation of an algorithm for identifying multiple sclerosis relapse in healthcare claims. J Med Econ. 2010;13(4):618-25.


HEOR, Health Economics Outcomes Research, Health Economics, Immunology

Dr. Nicole Engel-Nitz joined Optum in 2003. Her research focuses on oncology and rare diseases, with an emphasis on retrospective studies that integrate data from diverse sources, including insurance claims, medical charts, electronic health records, and other data sources.

Dr. Engel-Nitz has presented at national and international conferences, and has authored and coauthored peer-reviewed publications, including in The Oncologist and The American Journal of Managed Care.

She holds a Doctorate in Health Services Research, Policy and Administration from the University of Minnesota.

Published work

Engel-Nitz NM, Johnson MPJ, Bunner SH, Ryan KJ. Real-world costs of adverse events in first-line treatment of metastatic non-small cell lung cancer. Jrn Manag Care Spec Pharm, 2020 June;26(6):729-740.

Reyes C, Engel-Nitz N, DaCosta Byfield S, et al. Cost of disease progression in patients with metastatic breast, lung, and colorectal cancer. Oncologist. 2019 Feb 22.

Reyes C, Engel-Nitz N, DaCosta Byfield S, Ravelo A, Ogale S, Bancroft T, Anderson A, Chen M, Matasar M. Cost of disease progression in patients with chronic lymphocytic leukemia, acute myeloid leukemia, and non-Hodgkin's lymphoma. Oncologist. 2019 Sep; 24(9):1219-28.

Engel-Nitz NM, Liu Z, Blauer-Peterson C, Johnson J. Rare diseases in the era of big data: selection bias in small samples. ISPOR 20th Annual International Meeting workshop; 2015 May 16–20; Philadelphia, PA.

Engel-Nitz NM, Hao Y, Becker LK, Gerdes R. Costs and mortality of recurrent versus de novo hormone receptor-positive/HER2(-) metastatic breast cancer.Jrn Comp Eff Res. 2015 Aug;4(4):303-14.

Engel-Nitz NM, Yu EB, Becker LK, Small A. Service setting impact on costs for bevacizumab-treated oncology patients.Am Jrn Manag Care. 2014 Nov 1;20(11):e515-22.

Whyte JL, Engel-Nitz NM, Teitelbaum A, Gomez Rey G, Kallich JD. An evaluation of algorithms for identifying metastatic breast, lung, or colorectal cancer in administrative claims data.Med Care. 2015 July;53(7):e49-57.


Health economics outcomes research (HEOR), health economics, oncology, rare disease

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Dr. Noelle Gronroos joined Optum in 2021. Her epidemiological research has concentrated on cardiovascular and metabolic diseases, with a focus on methodology and biostatistics.

She has a Master of Public Health (MPH) from San Diego State University and a PhD in epidemiology from the University of Minnesota.

Published work 

Haring B, Gronroos N, Nettleton JA, von Ballmoos MC, Selvin E, Alonso A. Dietary protein intake and coronary heart disease in a large community-based cohort: Results from the atherosclerosis risk in communities (ARIC) study [corrected]. Public Library of Science One. 2014;9(10):e109552. doi: 10.1371/journal.pone.0109552.

Jensen PN, Gronroos NN, Chen LY, Folsom AR, deFilippi C, Heckbert SR, Alonso A. Incidence of and risk factors for sick sinus syndrome in the general population. Journal of the American College of Cardiology. 2014;64(6):531-38. doi: 10.1016/j.jacc.2014.03.056.

Gronroos NN, Chamberlain AM, Folsom AR, Soliman EZ, Agarwal SK, Nettleton JA, Alonso A. Fish, fish-derived n-3 fatty acids, and risk of incident atrial fibrillation in the Atherosclerosis Risk in Communities (ARIC) study. Public Library of Science One. 2012;7(5):e36686. doi: 10.1371/journal.pone.0036686.

Gronroos NN, Alonso A. Diet and risk of atrial fibrillation — epidemiologic and clinical evidence. Circulation Journal. 2010;74(10):2029-38.

Gronroos NN, Zouris JM, Wade AL. Odds of hospitalization among Marine Corps personnel by military occupational specialty and causative agents during Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF). Military Medicine. 2009;174(7):715-20.

Zouris J, Wade A, Gronroos N. (2007). Comparison of combat casualty statistics among U.S. Armed Forces during Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF).


Health economics outcomes research (HEOR), health economics, cardiovascular, endocrine and metabolic, study design and methods, program evaluation, risk adjustment, CMS Five Star Quality Ratings

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Dr. Rachel Halpern joined the Optum health economics and outcomes research (HEOR) team in 2005. As HEOR therapeutic lead for central nervous system and behavioral health (CNS/BH), Dr. Halpern conducts and oversees retrospective CNS/BH studies with administrative claims data and electronic health record data.

Before joining Optum, Dr. Halpern had eight years of health research experience, including military hospital market areas, managed care for persons with disabilities, and implementation of risk adjustment methodologies.

Dr. Halpern earned her Master of Public Health from the University of Michigan and her PhD in health services research and policy at the University of Minnesota. She has authored or co-authored over 30 articles.

Published work

Halpern R, Seare J, Tong J, Hartry A, Olaoye A, Aigbogun MS. Using electronic health records to estimate the prevalence of agitation in Alzheimer disease/dementia. International Journal of Geriatric Psychiatry. 2019;34(3):420-431.

Kalilani L, Halpern R, Seare J, Dedeken P. The challenges of assessing effectiveness of lacosamide using electronic medical record databases. Epilepsy & Behavior. 2018;85:195-199.

Ng-Mak D, Halpern R, Rajagopalan K, Loebel A. Hospitalization risk in bipolar disorder patients treated with lurasidone versus other atypical antipsychotics. Current Medical Research and Opinion. 2018;35(2):211-219.

Halpern R, Shah SN, Cappelleri JC, Masters ET, Clair A. Evaluating guideline-recommended pain medication use among patients with newly diagnosed fibromyalgia. Pain Practice. 2016;16(8):1027-1039.

Halpern R, Nadkarni A, Kalsekar I, et al. Medical costs and hospitalizations among patients with depression treated with adjunctive atypical antipsychotic therapy: An analysis of health insurance claims data. Annals of Pharmacotherapy. 2013;47(7-8):933-945.

Halpern R, Kothari S, Fuldeore M, Zarotsky V, Porter V, Dabbous O, Goldstein JL. GERD-related health care utilization, therapy and reasons for transfer of GERD patients between primary care providers and gastroenterologists in a U.S. managed care settingDigestive Diseases and Sciences. 2010;55(2):328-37.

Halpern R, Fuldeore MJ, Mody RR, Patel PA, Mikuls TR. The effect of serum urate on gout flares and their associated costsJournal of Clinical Rheumatology. 2009; 15(1):3-7.

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Jeff McPheeters joined Optum in 2011. As a research consultant, he translates broad research questions into actionable study designs. He assists in protocol development, dataset specification and statistical analysis.

His primary research areas include cancer, opioid use disorders and infectious disease. He has significant experience with retrospective study design, longitudinal data, survival analysis, cost analysis and cost‐effectiveness modeling.

Before joining Optum, McPheeters worked as a research analyst for Charles River Associates in Boston, Massachusetts. He earned his Bachelor of Arts in Economics from Boston College.


Health economics and outcomes research (HEOR), administrative claims, SAS

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Dr. Kristin Moore joined the Optum HEOR team in 2021. She has experience working on oncology, maternal and child health, and health services research projects.

Since joining Optum, she has worked on retrospective and prospective studies utilizing primary data collection methods, claims data and electronic health records (EHR).

Dr. Moore received her PhD in epidemiology from the University of North Carolina at Chapel Hill and her Master in Public Health from the University of Minnesota.

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Andrea Steffens joined Optum in 2021 as a senior researcher.

Prior to joining Optum, Steffens was an epidemiologist with the National Center for Immunization and Respiratory Diseases within the Centers for Disease Control and Prevention (CDC), where her research interests included the burden and severity of influenza and other respiratory viruses.

She also contributed to the COVID-19 pandemic response, leveraging electronic health data sources to better understand severe COVID-19 illness and the effectiveness of SARS-CoV-2 vaccines.

Steffens earned her Epidemiology Master of Public Health in Epidemiology from the University of Minnesota and her Bachelor of Arts from St. Olaf College.

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Rifky Tkatch, PhD

Rifky Tkatch, PhD, is the director of Primary Data Collection (PDC) for Optum Life Sciences health economics and outcomes research (HEOR). She provides oversight of project development and supports the business development activities for the PDC team.

Dr. Tkatch has been at Optum since 2015. She is trained as a social and health psychologist with expertise in research and program design and evaluation, survey development, and quantitative and qualitative analysis. She received her PhD in Psychology from Wayne State University, where she also completed an NIH-funded pre- and post-doctoral training program at the Institute of Gerontology. Dr. Tkatch completed her post-doctoral fellowship at the Karmanos Cancer Institute and the Department of Oncology at Wayne State University in Communication and Behavioral Oncology.

She has presented at numerous scientific conferences and published in several high-impact peer-reviewed journals, including Heart & Lung, Journal of Cancer Education, Journals of Gerontology and Aging and Mental Health.

Dr. Phani Veeranki is a physician-scientist with more than 10 years of experience in clinical epidemiology, policy analysis and economic valuations to demonstrate the value of health care interventions.

Dr. Veeranki has served as an advisor and investigator for numerous clinical trials, several cohort studies and cross-sectional surveys, along with hospital-based quality improvement projects.

He has deep knowledge and expertise in methodological approaches to address client needs in multiple therapeutic areas including respiratory, oncology, cardiovascular, neurology, psychiatry and rare/genetic diseases.

Additionally, he is an expert in retrospective and prospective cohort studies, clinical trials, medical chart review studies, preference-elicitation methods, expert-elicitation methods and health care economic models.

He has authored or coauthored more than 70 peer-reviewed publications and over 100 conference abstracts or presentations. His work has been published in leading journals including Journal of the American Medical Association, CHEST, BMJ and American Journal of Public Health.

In his current role with Optum life sciences, Dr. Veeranki leads a team of researchers in conducting retrospective cohort studies using administrative claims data and electronic health record data.

Before joining Optum, he held research positions in both academia and the life sciences industry. He holds both a doctorate and a Doctor of Public Health in epidemiology, and completed a fellowship in health outcomes research from Vanderbilt University Medical Center.

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Dr. Michelle Vu is a pharmacist and health economics and outcomes researcher, with experience in research and health care operations settings.

She has led pharmacoepidemiologic and pharmacoeconomic studies, and quality improvement evaluations, using administrative claims, electronic health records and adverse drug event reporting data sets.

Prior to joining the Optum health economics and outcomes research (HEOR) team, she designed risk-stratification models for clinical programs, conducted budget impact modeling and supported strategic opportunity analyses for MedImpact Healthcare Systems, Inc., a pharmacy benefit manager.

She completed her Doctor of Pharmacy and Master of Public Health at Mercer University in Atlanta, Georgia. She conducted her post-doctoral fellowship in medication safety and pharmacy outcomes research with the Veteran’s Health Administration.

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Since joining Optum in 1992, Valery Walker’s research has spanned numerous therapeutic areas and types of projects. She specializes in observational primary data collection studies linking administrative claims data to patient surveys and/or chart reviews.

Walker has experience in disease management programs, burden of illness studies, cross sectional and prospective observational “real world” studies, pragmatic trials, retrospective chart reviews, administrative claims and electronic health record (EHR) analysis. 

Her therapeutic areas cover work in osteoporosis, schizophrenia, depression, wound management, rheumatoid arthritis, fungal infections, osteoarthritis, gout, chronic obstructive pulmonary disease, diabetic macular edema, constipation and atopic dermatitis. 

Walker received her MSc from the Department of Clinical Epidemiology and Biostatistics at McMaster University, with a focus on the design, measurement and evaluation of health care research. She has published over 25 manuscripts in peer-reviewed journals.

Published work 

Harris SB, Mohammedi K, Bertolini M, White J, Walker V, Zhou FL, Anderson JE, Seufert J. Patient perspectives and experiences with basal insulin titration in type 2 diabetes in the United States: A cross-sectional survey. Diabetes Obes Metab. 2023;1‐5. doi:10. 1111/dom.14973

Brakenridge SC, Wilfret DA, Maislin G, Andrade KE, Walker V, May AK, Dankner WM, Bulger EM. Resolution of organ dysfunction as a predictor of long-term survival in necrotizing soft tissue infections: Analysis of the AB103 Clinical Composite Endpoint Study in Necrotizing Soft Tissue Infections trial and a retrospective claims database-linked chart study. J Trauma Acute Care Surg. 2021;91(2):384-392. DOI: 10.1097/TA.0000000000003183

Wei W, Ghorayeb E, Andria ML, Walker V, Schnitzer J, Kennedy M, Chen Z, Belland A, White J, Silverberg JI. A real-world study evaluating adeQUacy of Existing Systemic Treatments for patients with moderate-to-severe Atopic Dermatitis (AD-QUEST): Baseline treatment patterns and unmet needs assessment. Ann Allergy Asthma Immunol. 2019;123(4):381-388.

Strange C, Walker V, DePietro M, Tong J, Kurlander J, Carlyle M, Millette L, Wittbrodt E. Patient-reported outcomes of dual bronchodilator fixed-dose combination versus bronchodilator monotherapy in individuals with COPD. Int J Chron Obstruct Pulmon Dis. 2019:14;1377-1388.

Walker V, Patel H, Kurlander JL, Essoi B, Yang J, Mahableshwarkar AR, Samp JC, Akhras KS. Association between cognitive function and health care costs 3 months and 6 months after initiating antidepressant medication for depressive disorders. J Manag Care Spec Pharm. 2015 Sep;21(9):742-52.

Khanna PP, Shiozawa A, Walker V, Bancroft T, Essoi B, Akhras KS, Khanna D. Health-related quality of life and treatment satisfaction in patients with gout disease: results from a cross-sectional study in a managed care setting. Patient Prefer Adherence. 2015 Jul;9:971-81.


HEOR, Health Economics Outcomes Research, Health Economics, PDC, Primary Data Collection, Algorithm development

Yiran Zhang, PhD

Yiran Zhang, PhD, joined Optum in 2021 as a senior researcher in the Primary Data Collection (PDC) group. Dr. Zhang holds a PhD in Health Service Research from the University of Iowa, where she received systematic training on designing and conducting qualitative and quantitative research, and focused on pharmacy practice research among the older adult population.

Upon graduation, she completed a 2-year, post-doctoral training in an academia-industrial joint fellowship program at Virginia Commonwealth University and global pharmaceutical company Indivior, with a specific focus on health economics and outcomes research (HEOR). Prior to joining Optum, she was a manager at Indivior in the Global HEOR function, working in the therapeutic areas of opioid use disorder and schizophrenia. While at Indivior, she developed and implemented HEOR real-world evidence generation strategies to support market access of the company’s key assets, led the development of study protocol and analysis plan, and coordinated and executed scientific research and project management activities. Her research work has been shared through several national and international conferences, as well as publications in peer-reviewed journals, including the American Journal of Transplantation, Journal of the American Pharmacists Association and Research in Social and Administrative Pharmacy.

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