8,097 research outputs found
Average treatment effect estimation via random recursive partitioning
A new matching method is proposed for the estimation of the average treatment
effect of social policy interventions (e.g., training programs or health care
measures). Given an outcome variable, a treatment and a set of pre-treatment
covariates, the method is based on the examination of random recursive
partitions of the space of covariates using regression trees. A regression tree
is grown either on the treated or on the untreated individuals {\it only} using
as response variable a random permutation of the indexes 1... ( being the
number of units involved), while the indexes for the other group are predicted
using this tree. The procedure is replicated in order to rule out the effect of
specific permutations. The average treatment effect is estimated in each tree
by matching treated and untreated in the same terminal nodes. The final
estimator of the average treatment effect is obtained by averaging on all the
trees grown. The method does not require any specific model assumption apart
from the tree's complexity, which does not affect the estimator though. We show
that this method is either an instrument to check whether two samples can be
matched (by any method) and, when this is feasible, to obtain reliable
estimates of the average treatment effect. We further propose a graphical tool
to inspect the quality of the match. The method has been applied to the
National Supported Work Demonstration data, previously analyzed by Lalonde
(1986) and others
Invariant and Metric Free Proximities for Data Matching: An R Package
Data matching is a typical statistical problem in non experimental and/or observational studies or, more generally, in cross-sectional studies in which one or more data sets are to be compared. Several methods are available in the literature, most of which based on a particular metric or on statistical models, either parametric or nonparametric. In this paper we present two methods to calculate a proximity which have the property of being invariant under monotonic transformations. These methods require at most the notion of ordering. An open-source software in the form of a R package is also presented.
Rhinoclemmys areolata
Number of Pages: 2Integrative BiologyGeological Science
Solution Map Analysis of a Multiscale Drift-Diffusion Model for Organic Solar Cells
In this article we address the theoretical study of a multiscale
drift-diffusion (DD) model for the description of photoconversion mechanisms in
organic solar cells. The multiscale nature of the formulation is based on the
co-presence of light absorption, conversion and diffusion phenomena that occur
in the three-dimensional material bulk, of charge photoconversion phenomena
that occur at the two-dimensional material interface separating acceptor and
donor material phases, and of charge separation and subsequent charge transport
in each three-dimensional material phase to device terminals that are driven by
drift and diffusion electrical forces. The model accounts for the nonlinear
interaction among four species: excitons, polarons, electrons and holes, and
allows to quantitatively predict the electrical current collected at the device
contacts of the cell. Existence and uniqueness of weak solutions of the DD
system, as well as nonnegativity of all species concentrations, are proved in
the stationary regime via a solution map that is a variant of the Gummel
iteration commonly used in the treatment of the DD model for inorganic
semiconductors. The results are established upon assuming suitable restrictions
on the data and some regularity property on the mixed boundary value problem
for the Poisson equation. The theoretical conclusions are numerically validated
on the simulation of three-dimensional problems characterized by realistic
values of the physical parameters
Use of surface heat transfer measurements as a flow separation diagnostic in a two dimensional reflected oblique shock/turbulent boundary layer interaction
The feasibility of using streamwise surface heat transfer measurements to detect the presence of flow separation in a two-dimensional reflected oblique shock/turbulent boundary layer interaction is reported. Surface heat transfer and static pressure data are presented for attached and separated flows for a free stream nominal Mach number range of 2.5 to 3.5 and shock generator angles of 2 to 8 degrees. The static pressure data do show the characteristic triple inflection point distribution for the strongly separated flow cases. The corresponding surface heat transfer data show unique trends that correlate well with the static pressure determination of the extent of the separated flow region. For the incipient or weakly separated flow cases, the static pressure data do not exhibit the characteristic triple inflection point distribution. However, the same trends in the heat transfer data that are seen for the strongly separated flow cases are evident for the weakly separated flows. Hence, the heat transfer data can be used to determine the extent of weakly separated flows when the surface static pressure distributions often can not
cem: Software for Coarsened Exact Matching
This program is designed to improve causal inference via a method of matching that is widely applicable in observational data and easy to understand and use (if you understand how to draw a histogram, you will understand this method). The program implements the coarsened exact matching (CEM) algorithm, described below. CEM may be used alone or in combination with any existing matching method. This algorithm, and its statistical properties, are described in Iacus, King, and Porro (2008).
Social networks, happiness and health: from sentiment analysis to a multidimensional indicator of subjective well-being
This paper applies a novel technique of opinion analysis over social media
data with the aim of proposing a new indicator of perceived and subjective
well-being. This new index, namely SWBI, examines several dimension of
individual and social life. The indicator has been compared to some other
existing indexes of well-being and health conditions in Italy: the BES
(Benessere Equo Sostenibile), the incidence rate of influenza and the abundance
of PM10 in urban environments. SWBI is a daily measure available at province
level. BES data, currently available only for 2013 and 2014, are annual and
available at regional level. Flu data are weekly and distributed as regional
data and PM10 are collected daily for different cities. Due to the fact that
the time scale and space granularity of the different indexes varies, we apply
a novel statistical technique to discover nowcasting features and the classical
latent analysis to study the relationships among them. A preliminary analysis
suggest that the environmental and health conditions anticipate several
dimensions of the perception of well-being as measured by SWBI. Moreover, the
set of indicators included in the BES represent a latent dimension of
well-being which shares similarities with the latent dimension represented by
SWBI.Comment: 26 pages, 5 figur
Measuring Social Well Being in The Big Data Era: Asking or Listening?
The literature on well being measurement seems to suggest that "asking" for a
self-evaluation is the only way to estimate a complete and reliable measure of
well being. At the same time "not asking" is the only way to avoid biased
evaluations due to self-reporting. Here we propose a method for estimating the
welfare perception of a community simply "listening" to the conversations on
Social Network Sites. The Social Well Being Index (SWBI) and its components are
proposed through to an innovative technique of supervised sentiment analysis
called iSA which scales to any language and big data. As main methodological
advantages, this approach can estimate several aspects of social well being
directly from self-declared perceptions, instead of approximating it through
objective (but partial) quantitative variables like GDP; moreover
self-perceptions of welfare are spontaneous and not obtained as answers to
explicit questions that are proved to bias the result. As an application we
evaluate the SWBI in Italy through the period 2012-2015 through the analysis of
more than 143 millions of tweets.Comment: 40 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1512.0156
Notes on the ancient indian settlements of the upper Trombetas and Mapuera rivers, Pará, Brazil
A 'Relação' de 1728 de frei Francisco de São Manços, com a narrativa da primeira exploração da bacia Trombetas-Mapuera, no noroeste do Estado do Pará, embora publicada há mais de cem anos, é aqui, pela primeira vez, objeto de análise e de interpretação geográfica e etno-histórica. A importância do documento está em nomear e em localizar com aproximação cerca de 50 'nações' indÃgenas, quase todas ignoradas pelas fontes históricas e etnográficas posteriores, além de mencionar muitas de suas aldeias e de seus chefes. A reconstituição do itinerário permitiu concluir que a viagem do 'descobridor do Trombetas' transcorreu, na verdade, em grande parte, pelo Mapuera, seu afluente, até o planalto das Guianas. A informação etnográfica, embora limitada, inclui referências a dois nÃveis de chefia polÃtica e à guerra como meio de obter escravos destinados ao escambo por mercadorias.This is the first geographical and ethnohistorical analysis of the 1728 narrative of friar Francisco de São Manços on the first expedition to the Trombetas and Mapuera rivers in Northwestern Pará. The relevance of this document consists in the naming and approximate location of near 50 Indian 'nations', most of them not mentioned by later historical and ethnographical sources, including many names of their villages and local chiefs. The reconstruction of the expedition's course showed that São Manços, known as the "Trombetas' discoverer", had in fact traveled mostly through the Mapuera, its western tributary, up to the Guyana highlands. Outstanding in the author's scarce ethnographic information, there are references to a two levels political chieftainship, and to war as means to capture slaves targeted to trade for goods
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