377 research outputs found
Multi-GCN: Graph Convolutional Networks for Multi-View Networks, with Applications to Global Poverty
With the rapid expansion of mobile phone networks in developing countries,
large-scale graph machine learning has gained sudden relevance in the study of
global poverty. Recent applications range from humanitarian response and
poverty estimation to urban planning and epidemic containment. Yet the vast
majority of computational tools and algorithms used in these applications do
not account for the multi-view nature of social networks: people are related in
myriad ways, but most graph learning models treat relations as binary. In this
paper, we develop a graph-based convolutional network for learning on
multi-view networks. We show that this method outperforms state-of-the-art
semi-supervised learning algorithms on three different prediction tasks using
mobile phone datasets from three different developing countries. We also show
that, while designed specifically for use in poverty research, the algorithm
also outperforms existing benchmarks on a broader set of learning tasks on
multi-view networks, including node labelling in citation networks
Manipulation-Proof Machine Learning
An increasing number of decisions are guided by machine learning algorithms.
In many settings, from consumer credit to criminal justice, those decisions are
made by applying an estimator to data on an individual's observed behavior. But
when consequential decisions are encoded in rules, individuals may
strategically alter their behavior to achieve desired outcomes. This paper
develops a new class of estimator that is stable under manipulation, even when
the decision rule is fully transparent. We explicitly model the costs of
manipulating different behaviors, and identify decision rules that are stable
in equilibrium. Through a large field experiment in Kenya, we show that
decision rules estimated with our strategy-robust method outperform those based
on standard supervised learning approaches
Spectral aerosol optical depth retrievals by ground-based fourier transform infrared spectrometry
Aerosol Optical Depth (AOD) and the Ă
ngström Exponent (AE) have been calculated in the near infrared (NIR) and short-wave infrared (SWIR) spectral regions over a period of one year (May 2019âMay 2020) at the high-mountain Izaña Observatory (IZO) from Fourier Transform Infrared (FTIR) solar spectra. The high-resolution FTIR measurements were carried out coincidentally with Cimel CE318-T photometric observations in the framework of the Aerosol Robotic Network (AERONET). A spectral FTIR AOD was generated using two different approaches: by means of the selection of seven narrow FTIR micro-windows (centred at 1020.90, 1238.25, 1558.25, 1636.00, 2133.40, 2192.00, and 2314.20 nm) with negligible atmospheric gaseous absorption, and by using the CE318-AERONETâs response function in the near-coincident bands (1020 nm and 1640 nm) to degrade the high-resolution FTIR spectra. The FTIR system was absolutely calibrated by means of a continuous LangleyâPlot analysis over the 1-year period. An important temporal drift of the calibration constant was observed as a result of the environmental exposure of the FTIRâs external optical mirrors (linear degradation rate up to 1.75% monthâ1). The cross-validation of AERONET-FTIR databases documents an excellent agreement between both AOD products, with mean AOD differences below 0.004 and root-mean-squared errors below 0.006. A rather similar agreement was also found between AERONET and FTIR convolved bands, corroborating the suitability of low-resolution sunphotometers to retrieve high-quality AOD data in the NIR and SWIR domains. In addition, these results demonstrate that the methodology developed here is suitable to be applied to other FTIR spectrometers, such as portable and low-resolution FTIR instruments with a potentially higher spatial coverage. The spectral AOD dependence for the seven FTIR micro-windows have been also examined, observing a spectrally flat AOD behaviour for mineral dust particles (the typical atmospheric aerosols presented at IZO). A mean AE value of 0.53 ± 0.08 for pure mineral dust in the 1020â2314 nm spectral range was retrieved in this paper. A subsequent cross-validation with the MOPSMAP (Modeled optical properties of ensembles of aerosol particles) package has ensured the reliability of the FTIR dataset, with AE values between 0.36 to 0.60 for a typical mineral dust content at IZO of 100 cm and water-soluble particle (WASO) content ranging from 600 to 6000 cm. The new database generated in this study is believed to be the first long-term time series (1-year) of aerosol properties generated consistently in the NIR and SWIR ranges from ground-based FTIR spectrometry. As a consequence, the results presented here provide a very promising tool for the validation and subsequent improvement of satellite aerosol products as well as enhance the sensitivity to large particles of the existing databases, required to improve the estimation of the aerosolsâ radiative effect on climate
Subtropical trace gas profiles determined by ground-based FTIR spectroscopy at Izaña (28° N, 16° W): Five-year record, error analysis, and comparison with 3-D CTMs
International audienceWithin the framework of the NDSC (Network for the Detection of Stratospheric Change) ground-based FTIR solar absorption spectra have been routinely recorded at Izaña Observatory (28° N, 16° W) on Tenerife Island since March 1999. By analyzing the shape of the absorption lines, and their different temperature sensitivities, the vertical distribution of the absorbers can be retrieved. Unique time series of subtropical profiles of O3, HCl, HF, N2O, and CH4 are presented. The effects of both dynamical and chemical annually varying cycles can be seen in the retrieved profiles. These include enhanced upwelling and photochemistry in summer and a more disturbed atmosphere in winter, which are typical of the subtropical stratosphere. A detailed error analysis has been performed for each profile. The output from two different three-dimensional (3-D) chemical transport models (CTMs), which are forced by ECMWF analyses, are compared to the measured profiles. Both models agree well with the measurements in tracking abrupt variations in the atmospheric structure, e.g. due to tropical streamers, in particular for the lower stratosphere. Simulated and measured profiles also reflect similar dynamical and chemical annual cycles. However, the differences between their mixing ratios clearly exceed the error bars estimated for the measured profiles. Possible reasons for this are discussed
Quality assessment of ozone total column amounts as monitored by ground-based solar absorption spectrometry in the near infrared (> 3000 cm<sup>â1</sup>)
This study examines the possibility of ground-based remote-sensing ozone
total column amounts (OTC) from spectral signatures at 3040 and
4030 cmâ1. These spectral regions are routinely measured by the NDACC
(Network for the Detection of Atmospheric Composition Change) ground-based
FTIR (Fourier transform infraRed) experiments. In addition, they are
potentially detectable by the TCCON (Total Carbon Column Observing Network)
FTIR instruments. The ozone retrieval strategy presented here estimates the
OTC from NDACC FTIR high-resolution spectra with a theoretical precision of
about 2 and 5% in the 3040 and 4030 cmâ1 regions, respectively.
Empirically, these OTC products are validated by inter-comparison to FTIR OTC
reference retrievals in the 1000 cmâ1 spectral region (standard
reference for NDACC ozone products), using an 8-year FTIR time series
(2005â2012) taken at the subtropical ozone supersite of the Izaña
Atmospheric Observatory (Tenerife, Spain). Associated with the weaker ozone
signatures at the higher wave number regions, the 3040 and 4030 cmâ1
retrievals show lower vertical sensitivity than the 1000 cmâ1
retrievals. Nevertheless, we observe that the rather consistent variations
are detected: the variances of the 3040 cmâ1 and the 4030 cmâ1
retrievals agree within 90 and 75%, respectively, with the variance of the
1000 cmâ1 standard retrieval. Furthermore, all three retrievals show
very similar annual cycles. However, we observe a large systematic difference
of about 7% between the OTC obtained at 1000 and 3040 cmâ1,
indicating a significant inconsistency between the spectroscopic ozone
parameters (HITRAN, 2012) of both regions. Between the 1000 cm and the
4030 cmâ1 retrieval the systematic difference is only 2â3%.
Finally, the long-term stability of the OTC retrievals has also been
examined, observing that both near-infrared retrievals can monitor the
long-term OTC evolution, consistent with the 1000 cmâ1 reference data.
These findings demonstrate that recording the solar absorption spectra in the
3000 cmâ1 spectral region at high spectral resolution (about
0.005 cmâ1) might be useful for TCCON sites. Hence, both NDACC and
TCCON ground-based FTIR experiments might contribute to global ozone
databases
Promises and Pitfalls of Mobile Money in Afghanistan: Evidence from a Randomized Control Trial
ABSTRACT Despite substantial interest in the potential for mobile money to positively impact the lives of the poor, little empirical evidence exists to substantiate these claims. In this paper, we present the results of a field experiment in Afghanistan that was designed to increase adoption of mobile money, and determine if such adoption led to measurable changes in the lives of the adopters. The specific intervention we evaluate is a mobile salary payment program, in which a random subset of individuals of a large firm were transitioned into receiving their regular salaries in mobile money rather than in cash. We separately analyze the impact of this transition on both the employer and the individual employees. For the employer, there were immediate and significant cost savings; in a dangerous physical environment, they were able to effectively shift the costs of managing their salary supply chain to the mobile phone operator. For individual employees, however, the results were more ambiguous. Individuals who were transitioned onto mobile salary payments were more likely to use mobile money, and there is evidence that these accounts were used to accumulate small balances that may be indicative of savings. However, we find little consistent evidence that mobile money had an immediate or significant impact on several key indicators of individual wealth or well-being. Taken together, these results suggest that while mobile salary payments may increase the efficiency and transparency of traditional systems, in the short run the benefits may be realized by those making the payments, rather than by those receiving them
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