Mediation analysis has been extensively applied in psychological and
other social science research. Recently, a number of methodologists
have developed a formal theoretical framework for mediation analysis
from a modern causal inference perspective. In
Imai et al. (2010),
we have offered one such approach to causal mediation analysis that
formalizes identification, estimation, and sensitivity analysis in a
single framework. This approach has been used by a number of
substantive researchers and in subsequent work we have also further
extended it to more complex settings and developed new research
designs. In an insightful article, Pearl (2013) proposes an
alternative approach that are based on a set of assumptions weaker
than ours. In this commentary, we demonstrate that the theoretical
differences between our identification assumptions and his
alternative conditions are likely to be of little practical
relevance in the substantive research settings faced by most
psychologists and other social scientists. We also show that our
proposed estimation algorithms can be easily applied in the
situations discussed in Pearl (2013). The methods discussed in this
commentary and many more are implemented via open-source software
mediation
(Tingley et al., 2013).