99 research outputs found
When does the ID algorithm fail?
The ID algorithm solves the problem of identification of interventional
distributions of the form p(Y | do(a)) in graphical causal models, and has been
formulated in a number of ways [12, 9, 6]. The ID algorithm is sound (outputs
the correct functional of the observed data distribution whenever p(Y | do(a))
is identified in the causal model represented by the input graph), and complete
(explicitly flags as a failure any input p(Y | do(a)) whenever this
distribution is not identified in the causal model represented by the input
graph).
The reference [9] provides a result, the so called "hedge criterion"
(Corollary 3), which aims to give a graphical characterization of situations
when the ID algorithm fails to identify its input in terms of a structure in
the input graph called the hedge. While the ID algorithm is, indeed, a sound
and complete algorithm, and the hedge structure does arise whenever the input
distribution is not identified, Corollary 3 presented in [9] is incorrect as
stated. In this note, I outline the modern presentation of the ID algorithm,
discuss a simple counterexample to Corollary 3, and provide a number of
graphical characterizations of the ID algorithm failing to identify its input
distribution.Comment: arXiv admin note: substantial text overlap with arXiv:2108.0681
Counterfactual Graphical Models for Longitudinal Mediation Analysis with Unobserved Confounding
Questions concerning mediated causal effects are of great interest in
psychology, cognitive science, medicine, social science, public health, and
many other disciplines. For instance, about 60% of recent papers published in
leading journals in social psychology contain at least one mediation test
(Rucker, Preacher, Tormala, & Petty, 2011). Standard parametric approaches to
mediation analysis employ regression models, and either the "difference method"
(Judd & Kenny, 1981), more common in epidemiology, or the "product method"
(Baron & Kenny, 1986), more common in the social sciences. In this paper we
first discuss a known, but perhaps often unappreciated fact: that these
parametric approaches are a special case of a general counterfactual framework
for reasoning about causality first described by Neyman (1923), and Rubin
(1974), and linked to causal graphical models by J. Robins (1986), and Pearl
(2000). We then show a number of advantages of this framework. First, it makes
the strong assumptions underlying mediation analysis explicit. Second, it
avoids a number of problems present in the product and difference methods, such
as biased estimates of effects in certain cases. Finally, we show the
generality of this framework by proving a novel result which allows mediation
analysis to be applied to longitudinal settings with unobserved confounders.Comment: To appear in the 2012 Rumelhart prize special issue of Cognitive
Science honoring Judea Pear
Semiparametric theory for causal mediation analysis: Efficiency bounds, multiple robustness and sensitivity analysis
While estimation of the marginal (total) causal effect of a point exposure on
an outcome is arguably the most common objective of experimental and
observational studies in the health and social sciences, in recent years,
investigators have also become increasingly interested in mediation analysis.
Specifically, upon evaluating the total effect of the exposure, investigators
routinely wish to make inferences about the direct or indirect pathways of the
effect of the exposure, through a mediator variable or not, that occurs
subsequently to the exposure and prior to the outcome. Although powerful
semiparametric methodologies have been developed to analyze observational
studies that produce double robust and highly efficient estimates of the
marginal total causal effect, similar methods for mediation analysis are
currently lacking. Thus, this paper develops a general semiparametric framework
for obtaining inferences about so-called marginal natural direct and indirect
causal effects, while appropriately accounting for a large number of
pre-exposure confounding factors for the exposure and the mediator variables.
Our analytic framework is particularly appealing, because it gives new insights
on issues of efficiency and robustness in the context of mediation analysis. In
particular, we propose new multiply robust locally efficient estimators of the
marginal natural indirect and direct causal effects, and develop a novel double
robust sensitivity analysis framework for the assumption of ignorability of the
mediator variable.Comment: Published in at http://dx.doi.org/10.1214/12-AOS990 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Semiparametric Causal Sufficient Dimension Reduction Of High Dimensional Treatments
Cause-effect relationships are typically evaluated by comparing the outcome
responses to binary treatment values, representing two arms of a hypothetical
randomized controlled trial. However, in certain applications, treatments of
interest are continuous and high dimensional. For example, understanding the
causal relationship between severity of radiation therapy, represented by a
high dimensional vector of radiation exposure values and post-treatment side
effects is a problem of clinical interest in radiation oncology. An appropriate
strategy for making interpretable causal conclusions is to reduce the dimension
of treatment. If individual elements of a high dimensional treatment vector
weakly affect the outcome, but the overall relationship between the treatment
variable and the outcome is strong, careless approaches to dimension reduction
may not preserve this relationship. Moreover, methods developed for regression
problems do not transfer in a straightforward way to causal inference due to
confounding complications between the treatment and outcome. In this paper, we
use semiparametric inference theory for structural models to give a general
approach to causal sufficient dimension reduction of a high dimensional
treatment such that the cause-effect relationship between the treatment and
outcome is preserved. We illustrate the utility of our proposal through
simulations and a real data application in radiation oncology
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