18 research outputs found
Towards Bounding Causal Effects under Markov Equivalence
Predicting the effect of unseen interventions is a fundamental research
question across the data sciences. It is well established that, in general,
such questions cannot be answered definitively from observational data, e.g.,
as a consequence of unobserved confounding. A generalization of this task is to
determine non-trivial bounds on causal effects induced by the data, also known
as the task of partial causal identification. In the literature, several
algorithms have been developed for solving this problem. Most, however, require
a known parametric form or a fully specified causal diagram as input, which is
usually not available in practical applications. In this paper, we assume as
input a less informative structure known as a Partial Ancestral Graph, which
represents a Markov equivalence class of causal diagrams and is learnable from
observational data. In this more "data-driven" setting, we provide a systematic
algorithm to derive bounds on causal effects that can be computed analytically
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Hypothesis testing and causal inference with heterogeneous medical data
Learning from data which associations hold and are likely to hold in the future is a fundamental part of scientific discovery. With increasingly heterogeneous data collection practices, exemplified by passively collected electronic health records or high-dimensional genetic data with only few observed samples, biases and spurious correlations are prevalent. These are called spurious because they do not contribute to the effect being studied. In this context, the modelling assumptions of existing statistical tests and causal inference methods are often found inadequate and their practical utility diminished even though these models are increasingly used as decision-support tools in practice. This thesis investigates how modern computational techniques may broaden the fields of hypothesis testing and causal inference to handle the subtleties of large heterogeneous data sets, as well as simultaneously improve the robustness and theoretical understanding of machine learning algorithms using insights from causality and statistics.
The first part of this thesis is concerned with hypothesis testing. We develop a framework for hypothesis testing on set-valued data, a representation that faithfully describes many real-world phenomena including patient biomarker trajectories in the hospital. Using similar techniques, we develop next a two-sample test for making inference on selection-biased data, in the sense that not all individuals are equally likely to be included in the study, a fact that biases tests if not accounted for and if the desideratum is to obtain conclusions that are generally applicable. We conclude this section with an investigation of conditional independence in high-dimensional data, such as found in gene expression data, and propose a test using generative adversarial networks. The second part of this thesis is concerned with causal inference and discovery, with a special focus on the influence of unobserved confounders that distort the observed associations between variables and yet may not be ruled out or adjusted for using data alone. We start by demonstrating that unobserved confounders may bias substantially the generalization performance of machine learning algorithms trained with conventional learning paradigms such as empirical risk minimization. Acknowledging this spurious effect, we develop a new learning principle inspired by causal insights that provably generalizes to test data sampled from a larger set of distributions different from the training distribution. In the last chapter we consider the influence of unobserved confounders for causal discovery. We show that with some assumptions on the type and influence on the nature of unobserved confounding one may develop provably consistent causal discovery algorithms, formulated as a solution to a continuous optimization program
Functional Causal Bayesian Optimization
We propose functional causal Bayesian optimization (fCBO), a method for
finding interventions that optimize a target variable in a known causal graph.
fCBO extends the CBO family of methods to enable functional interventions,
which set a variable to be a deterministic function of other variables in the
graph. fCBO models the unknown objectives with Gaussian processes whose inputs
are defined in a reproducing kernel Hilbert space, thus allowing to compute
distances among vector-valued functions. In turn, this enables to sequentially
select functions to explore by maximizing an expected improvement acquisition
functional while keeping the typical computational tractability of standard BO
settings. We introduce graphical criteria that establish when considering
functional interventions allows attaining better target effects, and conditions
under which selected interventions are also optimal for conditional target
effects. We demonstrate the benefits of the method in a synthetic and in a
real-world causal graph
Navigating distance learning technologies using team teaching
In 2004, the American Association of Colleges of Nursing (AACN) adopted the position to move the current level of preparation necessary for advanced practice nurse (APN) roles from the master\u27s degree to the doctoral level. AACN also called for educating APNs and other nurses seeking top leadership and clinical roles in Doctor of Nursing Practice (DNP) Programs.
In September 2007, the Jefferson School of Nursing welcomed its first cohort of 18 DNP students. Students represented a wide variety of practice specialties including acute care, primary care, healthcare administration, population health, education and industry. Twenty students comprise the second cohort entering in September 2008. Nationwide, Jefferson is one of 79 schools of nursing offering a DNP degree