scholarly journals The impact of projection effects on cluster observables: stacked lensing and projected clustering

2020 ◽  
Vol 496 (4) ◽  
pp. 4468-4487
Author(s):  
Tomomi Sunayama ◽  
Youngsoo Park ◽  
Masahiro Takada ◽  
Yosuke Kobayashi ◽  
Takahiro Nishimichi ◽  
...  
Keyword(s):  
Selection Bias ◽  
Line Of Sight ◽  
Entire Sample ◽  
Projected Clustering ◽  
Small Scales ◽  
The Impact ◽  
Single Cluster

ABSTRACT An optical cluster finder inevitably suffers from projection effects, where it misidentifies a superposition of galaxies in multiple haloes along the line of sight as a single cluster. Using mock cluster catalogues built from cosmological N-body simulations, we quantify the impact of these projection effects with a particular focus on the observables of interest for cluster cosmology, namely the cluster-lensing and the cluster-clustering signals. We find that ‘observed’ clusters, i.e. clusters identified by our cluster finder algorithm, exhibit lensing and clustering signals that deviate from expectations based on a statistically isotropic halo model – while both signals agree with halo model expectations on small scales, they show unexpected boosts on large scales by up to a factor of 1.2 or 1.4, respectively. We identify the origin of these boosts as the inherent selection bias of optical cluster finders for clusters embedded within filaments aligned with the line of sight and show that a minority ($\sim 30{{\ \rm per\ cent}}$) of such clusters within the entire sample is responsible for this observed boost. We discuss the implications of our results on previous studies of optical cluster, as well as prospects for identifying and mitigating projection effects in future cluster cosmology analyses.

scholarly journals The halo model as a versatile tool to predict intrinsic alignments

2020 ◽  
Author(s):  
Maria Cristina Fortuna ◽  
Henk Hoekstra ◽  
Benjamin Joachimi ◽  
Harry Johnston ◽  
Nora Elisa Chisari ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Power Spectra ◽  
Stage Iv ◽  
Stage Iii ◽  
Radial Dependence ◽  
Additional Parameter ◽  
Small Scales ◽  
Cosmic Shear ◽  
Galaxy Populations ◽  
The Impact

Abstract Intrinsic alignments (IAs) of galaxies are an important contaminant for cosmic shear studies, but the modelling is complicated by the dependence of the signal on the source galaxy sample. In this paper, we use the halo model formalism to capture this diversity and examine its implications for Stage-III and Stage-IV cosmic shear surveys. We account for the different IA signatures at large and small scales, as well for the different contributions from central/satellite and red/blue galaxies, and we use realistic mocks to account for the characteristics of the galaxy populations as a function of redshift. We inform our model using the most recent observational findings: we include a luminosity dependence at both large and small scales and a radial dependence of the signal within the halo. We predict the impact of the total IA signal on the lensing angular power spectra, including the current uncertainties from the IA best-fits to illustrate the range of possible impact on the lensing signal: the lack of constraints for fainter galaxies is the main source of uncertainty for our predictions of the IA signal. We investigate how well effective models with limited degrees of freedom can account for the complexity of the IA signal. Although these lead to negligible biases for Stage-III surveys, we find that, for Stage-IV surveys, it is essential to at least include an additional parameter to capture the redshift dependence.

Patients Who Attend Alone at a First Memory Consultation: Are They a Specific Population,or Is It an Instance of Confounding Bias?

2019 ◽  
Vol 81 (1-2) ◽  
pp. 81-86
Author(s):  
Pierre Koskas ◽  
Mouna Romdhani ◽  
Olivier Drunat
Keyword(s):  
Selection Bias ◽  
Confounding Bias ◽  
Significant Difference ◽  
Comparison Groups ◽  
Methodological Problems ◽  
Group 2 ◽  
The Impact ◽  
First Time ◽  
State Examination ◽  
Group 1

As commonly happens in epidemiological research, none of the reported studies were totally free of methodological problems. Studies have considered the influence of social relationships on dementia, but the mechanisms underlying these associations are not perfectly understood. We look at the possible impact of selection bias. For their first memory consultation, patients may come alone or accompanied by a relative. Our objective is to better understand the impact of this factor by retrospective follow-up of geriatric memory outpatients over several years. All patients over 70 who were referred to Bretonneau Memory Clinic for the first time, between January 2006 and 2018, were included in the study. The patients who came alone formed group 1, the others, whatever type of relative accompanied them, formed group 2. We compared the Mini-Mental State Examination (MMSE) scores of patients; and for all patients who came twice for consultation with at least a 60-day interval, we compared their first MMSE with the MMSE performed at the second consultation. In total, 2,935 patients were included, aged 79.7 ± 8.4 years. Six hundred and twenty-five formed group 1 and 2,310 group 2. We found a significant difference in MMSE scores between the 2 groups of patients; and upon second consultation in group 2, but that difference was minor in group 1. Our finding of a possible confounding factor underlines the complexity of choosing comparison groups in order to minimize selection bias while maintaining clinical relevance.

scholarly journals Out of sight, out of mind? The impact of correlated clustering in substructure lensing

2021 ◽  
Author(s):  
Alexandres Lazar ◽  
James S Bullock ◽  
Michael Boylan-Kolchin ◽  
Robert Feldmann ◽  
Onur Çatmabacak ◽  
...  
Keyword(s):  
Dark Matter ◽  
Principal Axis ◽  
Major Axis ◽  
Line Of Sight ◽  
Gravitational Lenses ◽  
Local Clustering ◽  
Analytic Expression ◽  
Halo Masses ◽  
The Impact

Abstract A promising route for revealing the existence of dark matter structures on mass scales smaller than the faintest galaxies is through their effect on strong gravitational lenses. We examine the role of local, lens-proximate clustering in boosting the lensing probability relative to contributions from substructure and unclustered line-of-sight (LOS) haloes. Using two cosmological simulations that can resolve halo masses of Mhalo ≃ 109 M⊙ (in a simulation box of length Lbox ∼ 100 Mpc) and 107 M⊙ (Lbox ∼ 20 Mpc), we demonstrate that clustering in the vicinity of the lens host produces a clear enhancement relative to an assumption of unclustered haloes that persists to >20 Rvir. This enhancement exceeds estimates that use a two-halo term to account for clustering, particularly within 2 − 5 Rvir. We provide an analytic expression for this excess, clustered contribution. We find that local clustering boosts the expected count of 109 M⊙ perturbing haloes by ${\sim }35{{\ \rm per\ cent}}$ compared to substructure alone, a result that will significantly enhance expected signals for low-redshift (zl ≃ 0.2) lenses, where substructure contributes substantially compared to LOS haloes. We also find that the orientation of the lens with respect to the line of sight (e.g. whether the line of sight passes through the major axis of the lens) can also have a significant effect on the lensing signal, boosting counts by an additional $\sim 50{{\ \rm per\ cent}}$ compared to a random orientations. This could be important if discovered lenses are biased to be oriented along their principal axis.

Women on the board of directors and corporate tax aggressiveness in Australia

2016 ◽  
Vol 29 (3) ◽  
pp. 313-331 ◽  
Author(s):  
Grant Richardson ◽  
Grantley Taylor ◽  
Roman Lanis
Keyword(s):  
Board Of Directors ◽  
Selection Bias ◽  
Tax Avoidance ◽  
Multivariate Regression Analysis ◽  
Corporate Tax ◽  
Content Type ◽  
Tax Aggressiveness ◽  
Self Selection ◽  
The Board Of Directors ◽  
The Impact

Purpose This paper aims to investigate the impact of women on the board of directors on corporate tax avoidance in Australia. Design/methodology/approach The authors use multivariate regression analysis to test the association between the presence of female directors on the board and tax aggressiveness. They also test for self-selection bias in the regression model by using the two-stage Heckman procedure. Findings This paper finds that relative to there being one female board member, high (i.e. greater than one member) female presence on the board of directors reduces the likelihood of tax aggressiveness. The results are robust after controlling for self-selection bias and using several alternative measures of tax aggressiveness. Research limitations/implications This study extends the extant literature on corporate governance and tax aggressiveness. This study is subject to several caveats. First, the sample is restricted to publicly listed Australian firms. Second, this study only examines the issue of women on the board of directors and tax aggressiveness in the context of Australia. Practical implications This research is timely, as there has been increased pressure by government bodies in Australia and globally to develop policies to increase female representation on the board of directors. Originality/value This study is the first to provide empirical evidence concerning the association between the presence of women on the board of directors and tax aggressiveness.

scholarly journals The impact of line-of-sight structures on measuring H0 with strong lensing time delays

2021 ◽  
Vol 504 (2) ◽  
pp. 2224-2234
Author(s):  
Nan Li ◽  
Christoph Becker ◽  
Simon Dye
Keyword(s):  
Time Delays ◽  
Line Of Sight ◽  
Lens Model ◽  
Local Universe ◽  
Significant Discrepancy ◽  
Turn On ◽  
Strong Lensing ◽  
Systematic Effects ◽  
The Impact ◽  
Realistic Line

ABSTRACT Measurements of the Hubble–Lemaitre constant from early- and local-Universe observations show a significant discrepancy. In an attempt to understand the origin of this mismatch, independent techniques to measure H0 are required. One such technique, strong lensing time delays, is set to become a leading contender amongst the myriad methods due to forthcoming large strong lens samples. It is therefore critical to understand the systematic effects inherent in this method. In this paper, we quantify the influence of additional structures along the line of sight by adopting realistic light-cones derived from the cosmoDC2 semi-analytical extragalactic catalogue. Using multiple-lens plane ray tracing to create a set of simulated strong lensing systems, we have investigated the impact of line-of-sight structures on time-delay measurements and in turn, on the inferred value of H0. We have also tested the reliability of existing procedures for correcting for line-of-sight effects. We find that if the integrated contribution of the line-of-sight structures is close to a uniform mass sheet, the bias in H0 can be adequately corrected by including a constant external convergence κext in the lens model. However, for realistic line-of-sight structures comprising many galaxies at different redshifts, this simple correction overestimates the bias by an amount that depends linearly on the median external convergence. We therefore conclude that lens modelling must incorporate multiple-lens planes to account for line-of-sight structures for accurate and precise inference of H0.

The impact of selection bias on measurement of noninvasive test accuracy

1993 ◽  
Vol 72 (2) ◽  
pp. 223-225 ◽  
Author(s):  
David M. Salerno ◽  
Kyuhyun Wang ◽  
Irvin F. Goldenberg ◽  
Robert A. Van Tassel
Keyword(s):  
Selection Bias ◽  
Test Accuracy ◽  
Noninvasive Test ◽  
The Impact

Quantifying the Impact of Selection Bias Caused by Nonparticipation in a Case–Control Study of Mobile Phone Use

2009 ◽  
Vol 19 (1) ◽  
pp. 33-41.e1 ◽  
Author(s):  
Martine Vrijheid ◽  
Lesley Richardson ◽  
Bruce K. Armstrong ◽  
Anssi Auvinen ◽  
Gabriele Berg ◽  
...  
Keyword(s):  
Mobile Phone ◽  
Selection Bias ◽  
Case Control Study ◽  
Case Control ◽  
Mobile Phone Use ◽  
The Impact ◽  
Control Study

scholarly journals Impact of accelerometer based in physical layer wireless networks

2018 ◽  
Vol 7 (2.5) ◽  
pp. 15
Author(s):  
Zuhanis Mansor ◽  
Muhammad Khairulanwar bin Zulkafli
Keyword(s):  
Wireless Communication ◽  
Landscape Position ◽  
Line Of Sight ◽  
Noise Power ◽  
Signal Power ◽  
Propagation Channel ◽  
Signal To Noise ◽  
Downlink Throughput ◽  
The Impact ◽  
Non Line Of Sight

The initial deployments of antenna in the handset consist of fixed non-rotated antenna for transmitting and receiving the signal in the wireless communication scenario. However, link correlation at the UE shows very bad performance when the handset rotates in landscape position. This paper evaluates the impact of accelerometer on the downlink propagation channel of 3G smartphone for non-line-of-sight links. The performance average received signal power is studied for user equipment. Results show that the exploitation of an accelerometer provide better performance in terms of received signal power when the handset rotated from portrait to landscape position. It can be concluded that the deployment of accelerometer can be used to improve existing 3G smartphone received signal. Results also indicate that accelerometer can be used to improve downlink throughput since the signal-to-noise-power is increased by approximately 16%.

scholarly journals Meta-Analytic Findings in the Self-Controlled Motor Learning Literature: Underpowered, Biased, and Lacking Evidential Value

2021 ◽  
Author(s):  
Brad McKay ◽  
Zachary Yantha ◽  
Julia Hussien ◽  
Michael J Carter ◽  
Diane M. Ste-Marie
Keyword(s):  
Motor Learning ◽  
Weight Function ◽  
Selection Bias ◽  
The Self ◽  
Sensitivity Analyses ◽  
P Value ◽  
Function Model ◽  
Evidential Value ◽  
Significant Difference ◽  
The Impact

The self-controlled motor learning literature consists of experiments that compare a group of learners who are provided with a choice over an aspect of their practice environment to a group who are yoked to those choices. A qualitative review of the literature suggests an unambiguous benefit from self-controlled practice. A meta-analysis was conducted on the effects of self-controlled practice on retention test performance measures with a focus on assessing and potentially correcting for selection bias in the literature, such as publication bias and p-hacking. First, a naïve random effects model was fit to the data and a moderate benefit of self-controlled practice, g=.44 (k= 52,N= 3134,95%CI[.31, .56]), was found. Second, publication status was added to the model as a potential moderator, revealing a significant difference between published and unpublished findings, with only the former reporting a benefit of self-controlled practice. Third, to investigate and adjust for the impact of selectively reporting statistically significant results, a weight-function model was fit to the data with a one-tailed p-value cutpoint of .025. The weight-function model revealed substantial selection bias and estimated the true average effect of self-controlled practice as g=.107 (95%CI[.047, .18]). P-curve analyses were conducted on the statistically significant results published in the literature and the outcome suggested a lack of evidential value. Fourth, a suite of sensitivity analyses were conducted to evaluate the robustness of these results, all of which converged on trivially small effect estimates. Overall, our results suggest the benefit of self-controlled practice on motor learning is small and not currently distinguishable from zero.

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