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Nima Hejazi, Ph.D.

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Biography
Weill Cornell Medicine, New York, NYPostdoc2022Causal Inference, Targeted Machine Learning
UC Berkeley, Berkeley, CAPhD2021Biostatistics
UC Berkeley, Berkeley, CAMA2017Biostatistics
UC Berkeley, Berkeley, CABA2015Molecular and Cell Biology, Psychology, Public Health
2024 - 2026
CFAR Early Career Investigator Development Award
2022
ACIC/SCI Early Career Scholar Travel Award
2021 - 2022
NSF Mathematical Sciences Postdoctoral Research Fellowship (MSPRF)
2020
The Wallace Lowe Fellowship
2019
Tom Ten Have Memorial Award (for "exceptionally creative or skillful research in causal inference")
2019
The Eki and Nobuta Akahoshi and Seiko Baba Brodbeck Endowed Fund Scholarship
2018
The Wellness Scholarship in Honor of Chin Long Chiang
2017 - 2018
NIH/NLM BD2K Biomedical Big Data (BBD) Training Program Fellowship
2017
Honorable Mention for the Tom Ten Have Memorial Award

Overview
My research explores how advances in causal inference, statistical machine learning, and computational statistics can empower discovery in the biomedical and health sciences. I focus primarily on the development of model-agnostic, assumption-lean statistical inference procedures, doing so while emphasizing a science-first, translational philosophy that stresses the rich interplay between the applied sciences and statistical methodology: how emerging questions in the former spur advances in the latter, which, in turn, help to refine scientific discoveries. To accomplish this, my work leverages causal inference as a framework to translate scientific questions into precise, causally interpretable statistical estimands, and then aims to obtain inference about these from data by formulating analytic methods that incorporate flexible, adaptive modeling strategies (i.e., machine learning), to avoid imposing restrictions that may not be justified by domain knowledge, and semi-parametric efficiency theory for best-in-class uncertainty quantification. I am also interested in statistical instrumentation---that is, high-performance computing and open-source software and programming---to push the boundaries of statistical methodology and to promote transparency and reproducibility in the practice of applied statistics and data science.

My methodological work draws upon tools and ideas from semi- and non-parametric statistics, high-dimensional and large-scale inference, de-biased or targeted machine learning (e.g., targeted minimum loss estimation, sieve estimation), and computational statistics. Areas of recent focus include the study of inference on treatment effects from data collected via biased or outcome-dependent sampling designs, including extensions to sequentially adaptive sampling schemes; causal effect heterogeneity for optimal treatment regime and subgroup discovery; efficient semi-parametric or causal machine learning approaches for evaluating dose-response phenomena; causal mediation analysis (i.e., path-specific direct and indirect effects) for investigating questions of mechanism; and safely drawing causal inferences from data exhibiting network dependence or interference structures.

Inspired by John Tukey's sentiment that "the best thing about being a statistician is that you get to play in everyone's backyard", my past substantive collaborations have spanned diverse areas of the biomedical and public health sciences---from toxicology and computational biology to environmental health and nutritional epidemiology. Recently, though, I've been captivated by the rich scientific and statistical problems that abound in the infectious disease sciences, especially in efforts to evaluate investigational therapeutics and preventive vaccines in randomized controlled clinical trials and observational studies. My work has contributed novel methods and insights for characterizing immune correlates (surrogate endpoints) in vaccine efficacy trials of HIV and COVID-19; for comparing therapeutics in studies of COVID-19 and TB/HIV co-infection; and for identifying post-acute sequelae of COVID-19.

Here are a few reflections on the intertwined philosophies of science and of statistics that have shaped my own perspective:

"Far better an approximate answer to the right question, which is often vague, than the exact answer to the wrong question, which can always be made precise." --John Tukey

"Everyone is sure of this [that errors are normally distributed]...since the experimentalists believe that it is a mathematical theorem, and the mathematicians that it is an experimentally determined fact." --Henri Poincare

"Science is the belief in the ignorance of experts." --Richard Feynman

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Funded by the NIH National Center for Advancing Translational Sciences through its Clinical and Translational Science Awards Program, grant number UL1TR002541.