453 research outputs found
More Data Can Lead Us Astray: Active Data Acquisition in the Presence of Label Bias
An increased awareness concerning risks of algorithmic bias has driven a
surge of efforts around bias mitigation strategies. A vast majority of the
proposed approaches fall under one of two categories: (1) imposing algorithmic
fairness constraints on predictive models, and (2) collecting additional
training samples. Most recently and at the intersection of these two
categories, methods that propose active learning under fairness constraints
have been developed. However, proposed bias mitigation strategies typically
overlook the bias presented in the observed labels. In this work, we study
fairness considerations of active data collection strategies in the presence of
label bias. We first present an overview of different types of label bias in
the context of supervised learning systems. We then empirically show that, when
overlooking label bias, collecting more data can aggravate bias, and imposing
fairness constraints that rely on the observed labels in the data collection
process may not address the problem. Our results illustrate the unintended
consequences of deploying a model that attempts to mitigate a single type of
bias while neglecting others, emphasizing the importance of explicitly
differentiating between the types of bias that fairness-aware algorithms aim to
address, and highlighting the risks of neglecting label bias during data
collection
Mitigating Label Bias via Decoupled Confident Learning
Growing concerns regarding algorithmic fairness have led to a surge in
methodologies to mitigate algorithmic bias. However, such methodologies largely
assume that observed labels in training data are correct. This is problematic
because bias in labels is pervasive across important domains, including
healthcare, hiring, and content moderation. In particular, human-generated
labels are prone to encoding societal biases. While the presence of labeling
bias has been discussed conceptually, there is a lack of methodologies to
address this problem. We propose a pruning method -- Decoupled Confident
Learning (DeCoLe) -- specifically designed to mitigate label bias. After
illustrating its performance on a synthetic dataset, we apply DeCoLe in the
context of hate speech detection, where label bias has been recognized as an
important challenge, and show that it successfully identifies biased labels and
outperforms competing approaches.Comment: AI & HCI Workshop at the 40th International Conference on Machine
Learning (ICML), Honolulu, Hawaii, USA. 202
The Signature of Primordial Grain Growth in the Polarized Light of the AU Mic Debris Disk
We have used the Hubble Space Telescope/ACS coronagraph to make polarization
maps of the AU Mic debris disk. The fractional linear polarization rises
monotonically from about 0.05 to 0.4 between 20 and 80 AU. The polarization is
perpendicular to the disk, indicating that the scattered light originates from
micron sized grains in an optically thin disk. Disk models, which
simultaneously fit the surface brightness and polarization, show that the inner
disk (< 40-50 AU) is depleted of micron-sized dust by a factor of more than
300, which means that the disk is collision dominated. The grains have high
maximum linear polarization and strong forward scattering. Spherical grains
composed of conventional materials cannot reproduce these optical properties. A
Mie/Maxwell-Garnett analysis implicates highly porous (91-94%) particles. In
the inner Solar System, porous particles form in cometary dust, where the
sublimation of ices leaves a "bird's nest" of refractory organic and silicate
material. In AU Mic, the grain porosity may be primordial, because the dust
"birth ring" lies beyond the ice sublimation point. The observed porosities
span the range of values implied by laboratory studies of particle coagulation
by ballistic cluster-cluster aggregation. To avoid compactification, the upper
size limit for the parent bodies is in the decimeter range, in agreement with
theoretical predictions based on collisional lifetime arguments. Consequently,
AU Mic may exhibit the signature of the primordial agglomeration process
whereby interstellar grains first assembled to form macroscopic objects.Comment: 12 pages, 8 figures, ApJ, in pres
The competitive landscape of high-frequency trading firms
Abstract
We examine product differentiation in the high-frequency trading (HFT) industry, where the “products” are secretive proprietary trading strategies. We demonstrate how principal component analysis can be used to detect underlying strategies common to multiple HFT firms and show that there are three product categories with distinct attributes. We study how HFT competition in each product category affects the market environment and present evidence that indicates how it influences the short-horizon volatility of stocks as well as the viability of trading venues.
Received October 10, 2016; editorial decision September 30, 2017 by Editor Itay Goldstein. Authors have furnished an Internet Appendix, which is available on the Oxford University Press Web site next to the link to the final published paper online.</jats:p
The complementarity of astrometric and radial velocity exoplanet observations - Determining exoplanet mass with astrometric snapshots
We obtain full information on the orbital parameters by combining radial
velocity and astrometric measurements by means of Bayesian inference. We sample
the parameter probability densities of orbital model parameters with a Markov
chain Monte Carlo (McMC) method in simulated observational scenarios to test
the detectability of planets with orbital periods longer than the observational
timelines. We show that, when fitting model parameters simultaneously to
measurements from both sources, it is possible to extract much more information
from the measurements than when using either source alone. We demonstrate this
by studying the orbit of recently found extra-solar planet HD 154345 b.Comment: 6 pages, 9 figures. Accepted to A&
Methods for exomoon characterisation: combining transit photometry and the Rossiter-McLaughlin effect
It has been suggested that moons around transiting exoplanets may cause
observable signal in transit photometry or in the Rossiter-McLaughlin (RM)
effect. In this paper a detailed analysis of parameter reconstruction from the
RM effect is presented for various planet-moon configurations, described with
20 parameters. We also demonstrate the benefits of combining photometry with
the RM effect. We simulated 2.7x10^9 configurations of a generic transiting
system to map the confidence region of the parameters of the moon, find the
correlated parameters and determine the validity of reconstructions. The main
conclusion is that the strictest constraints from the RM effect are expected
for the radius of the moon. In some cases there is also meaningful information
on its orbital period. When the transit time of the moon is exactly known, for
example, from transit photometry, the angle parameters of the moon's orbit will
also be constrained from the RM effect. From transit light curves the mass can
be determined, and combining this result with the radius from the RM effect,
the experimental determination of the density of the moon is also possible.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Extrasolar planets and brown dwarfs around A-F type stars VI. High precision RV survey of early type dwarfs with HARPS
(Abridged) Aims: Systematic surveys to search for exoplanets have been mostly
dedicated to solar-type stars sofar. We developed in 2004 a method to extend
such searches to earlier A-F type dwarfs and started spectroscopic surveys to
search for planets and quantify the detection limit achievable when taking into
account the stars properties and their actual levels of intrinsic variations.
We give here the first results of our southern survey with HARPS.
Results: 1) 64% of the 170 stars with enough data points are found to be
variable. 20 are found to be binaries or candidate binaries (with stars or
brown dwarfs). More than 80% or the latest type stars (once binaries are
removed) are intrinsically variable at a 2 m/s precision level. Stars with
earlier spectral type (B-V <= 0.2) are either variable or associated to levels
of uncertainties comparable to the RV rms observed on variable stars of same
B-V. 2) We have detected one long-period planetary system around an F6IV-V
star. 3) We have quantified the jitter due to stellar activity and we show that
taking into account this jitter in addition to the stellar parameters, it is
still possible to detect planets with HARPS with periods of 3 days (resp. 10
days and 100 days) on 91% (resp. 83%, 61%) of them. We show that even the
earliest spectral type stars are accessible to this type of search, provided
they have a low vsini and low levels of activity. 4) Taking into account the
present data, we compute the actually achieved detection limits for 107 targets
and discuss the limits as a function of B-V. Given the data at hand, our survey
is sensitive to short-period (few days) planets and to longer ones (100 days)
at a lower extent (latest type stars). We derive first constrains on the
presence of planets around A-F stars for these ranges of periods.Comment: 18 pages, 12 figures, 5 tables, A&A accepte
A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups
Nearby late-type stars are excellent targets for seeking young objects in
stellar associations and moving groups. The origin of these structures is still
misunderstood, and lists of moving group members often change with time and
also from author to author. Most members of these groups have been identified
by means of kinematic criteria, leading to an important contamination of
previous lists by old field stars. We attempt to identify unambiguous moving
group members among a sample of nearby-late type stars by studying their
kinematics, lithium abundance, chromospheric activity, and other age-related
properties. High-resolution echelle spectra () of a sample of
nearby late-type stars are used to derive accurate radial velocities that are
combined with the precise Hipparcos parallaxes and proper motions to compute
galactic-spatial velocity components. Stars are classified as possible members
of the classical moving groups according to their kinematics. The spectra are
also used to study several age-related properties for young late-type stars,
i.e., the equivalent width of the lithium Li~{\sc i} \space 6707.8 \space \AA
\space line or the index. Additional information like X-ray
fluxes from the ROSAT All-Sky Survey or the presence of debris discs is also
taken into account. The different age estimators are compared and the moving
group membership of the kinematically selected candidates are discussed. From a
total list of 405 nearby stars, 102 have been classified as moving group
candidates according to their kinematics. i.e., only 25.2 \% of the
sample. The number reduces when age estimates are considered, and only 26
moving group candidates (25.5\% of the 102 candidates) have ages in agreement
with the star having the same age as an MG memberComment: 39 pages, 11 figures. Accepted for publication in Astronomy \&
Astrophysic
Price impact asymmetry of institutional trading in Chinese stock market
The asymmetric price impact between the institutional purchases and sales of
32 liquid stocks in Chinese stock markets in year 2003 is carefully studied. We
analyze the price impact in both drawup and drawdown trends with consecutive
positive and negative daily price changes, and test the dependence of the price
impact asymmetry on the market condition. For most of the stocks institutional
sales have a larger price impact than institutional purchases, and larger
impact of institutional purchases only exists in few stocks with primarily
increasing tendencies. We further study the mean return of trades surrounding
institutional transactions, and find the asymmetric behavior also exists before
and after institutional transactions. A new variable is proposed to investigate
the order book structure, and it can partially explain the price impact of
institutional transactions. A linear regression for the price impact of
institutional transactions further confirms our finding that institutional
sales primarily have a larger price impact than institutional purchases in the
bearish year 2003.Comment: 14 pages, 3 figure
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