Presence Of Selection Effects Research Articles

Dwarf AGNs from variability for the origins of seeds (DAVOS): Intermediate-mass black hole demographics from optical synoptic surveys

ABSTRACT We present a phenomenological forward Monte Carlo model for forecasting the population of active galactic nuclei (AGNs) in dwarf galaxies observable via their optical variability. Our model accounts for expected changes in the spectral energy distribution of AGNs in the intermediate-mass black hole (IMBH) mass range and uses observational constraints on optical variability as a function of black hole (BH) mass to generate mock light curves. Adopting several different models for the BH occupation function, including one for off-nuclear IMBHs, we quantify differences in the predicted local AGN mass and luminosity functions in dwarf galaxies. As a result, we are able to model the fraction of variable AGNs as a function of important galaxy host properties, such as host galaxy stellar mass, in the presence of selection effects. We find that our adopted occupation fractions for the ‘heavy’ and ‘light’ initial BH seeding scenarios can be distinguished with variability at the 2–3σ level for galaxy host stellar masses below ∼108M⊙ with data from the upcoming Vera C. Rubin Observatory. We also demonstrate the prevalence of a selection bias whereby recovered IMBH masses fall, on average, above the predicted value from the local host galaxy–BH mass scaling relation with the strength of this bias dependent on the survey sensitivity. Our methodology can be used more broadly to calibrate AGN demographic studies in synoptic surveys. Finally, we show that a targeted ∼ hourly cadence program over a few nights with the Rubin Observatory can provide strong constraints on IMBH masses given their expected rapid variability time-scales.

Unbiased likelihood-free inference of the Hubble constant from light standard sirens

Multi-messenger observations of binary neutron star mergers offer a promising path towards resolution of the Hubble constant ($H_0$) tension, provided their constraints are shown to be free from systematics such as the Malmquist bias. In the traditional Bayesian framework, accounting for selection effects in the likelihood requires calculation of the expected number (or fraction) of detections as a function of the parameters describing the population and cosmology; a potentially costly and/or inaccurate process. This calculation can, however, be bypassed completely by performing the inference in a framework in which the likelihood is never explicitly calculated, but instead fit using forward simulations of the data, which naturally include the selection. This is Likelihood-Free Inference (LFI). Here, we use density-estimation LFI, coupled to neural-network-based data compression, to infer $H_0$ from mock catalogues of binary neutron star mergers, given noisy redshift, distance and peculiar velocity estimates for each object. We demonstrate that LFI yields statistically unbiased estimates of $H_0$ in the presence of selection effects, with precision matching that of sampling the full Bayesian hierarchical model. Marginalizing over the bias increases the $H_0$ uncertainty by only $6\%$ for training sets consisting of $O(10^4)$ populations. The resulting LFI framework is applicable to population-level inference problems with selection effects across astrophysics.

The Selection of Litigation against Government Agencies: Evidence from China

AbstractWe test the relevance of the selection theory of litigation in a contemporary, civil law setting, using Chinese judicial data that span 25 years regarding lawsuits against government agencies. Civil law systems may be characterized by lower costs of litigation and lower rates of settlement than the U.S. legal system, and therefore the presence of selection effects cannot be assumed. We show that selection effects are indeed manifest in Chinese administrative litigation, and suggest that this may be explained by hidden or intangible litigation costs. Our test for selection effects builds on the approach of previous U.S. studies and potentially allows the identification of selection effects to help improve inferences from decided cases. Finally, we examine patterns of settlement and plaintiff wins in pre-litigation administrative appeals in China, and do not find sufficient evidence for selection effects in this process. This could potentially be explained if most appellants pursuing administrative appeals do not intend to litigate.

Evaluation of Development Programs: Using Regressions to Assess the Impact of Complex Interventions

There is a growing interest in extending project evaluation methods to the evaluation of programs: complex interventions involving multiple activities. In general a program evaluation cannot be based on separate evaluations of its components since interactions between the activities are likely to be important. We propose a measure of program impact, the total program effect (TPE), which is an extension of the average treatment effect on the treated (ATET). Regression techniques can be applied to observational data from a representative sample to estimate the TPE for complex interventions in the presence of selection effects and treatment heterogeneity. As an example we present an estimate of the TPE for a rural water supply and sanitation program in Mozambique. Estimating the TPE from randomized controlled trials would appear to be an alternative; however, the scope for using RCTs in this context is limited.

Intervening Mg ii absorption systems from the SDSS DR12 quasar spectra

We present the catalogue of the Mg II absorption systems detected at a high significance level using an automated search algorithm in the spectra of quasars from the twelfth data release of the Sloan Digital Sky Survey. A total of 266,433 background quasars were searched for the presence of absorption systems in their spectra. The continuum modelling for the quasar spectra was performed using a mean filter. A pseudo-continuum derived using a median filter was used to trace the emission lines. The absorption system catalogue contains 39,694 Mg II systems detected at a 6.0, 3.0$\sigma$ level respectively for the two lines of the doublet. The catalogue was constrained to an absorption line redshift of 0.35 $\le$ z$_{2796}$ $\le$ 2.3. The rest-frame equivalent width of the $\lambda$2796 line ranges between 0.2 $\le$ W$_r$ $\le$ 6.2 $\AA$. Using Gaussian-noise only simulations we estimate a false positive rate of 7.7 per cent in the catalogue. We measured the number density $\partial N^{2796}/\partial z$ of Mg II absorbers and find evidence for steeper evolution of the systems with W$_r \ge$ 1.2 $\AA$ at low redshifts (z$_{2796}$ $\le$ 1.0), consistent with other earlier studies. A suite of null tests over the redshift range 0.5 $\le$ z$_{2796}$ $\le$ 1.5 was used to study the presence of systematics and selection effects like the dependence of the number density evolution of the absorption systems on the properties of the background quasar spectra. The null tests do not indicate the presence of any selection effects in the absorption catalogue if the quasars with spectral signal-to-noise level less than 5.0 are removed. The resultant catalogue contains 36,981 absorption systems. The Mg II absorption catalogue is publicly available and can be downloaded from the link http://srini.ph.unimelb.edu.au/mgii.php

Testing for Change in Procedural Standards, with Application to Bell Atlantic v. Twombly

AbstractQuantifying change in legal standards—in the sense of change in the propensity of judges to decide cases a certain way—presents a vexing problem. In response to a change in the behavior of courts, plaintiffs and defendants will adjust their patterns of filing and settling cases. Models of the selection of disputes for litigation predict that when legal standards change, the rate at which plaintiffs prevail in litigation will not predictably change; if so, changes in legal standards cannot be measured with data on court outcomes. I consider both the Priest and Klein divergent-expectations model and the Bebchuk asymmetric-information model to develop a methodology for measuring changes in procedural standards in the presence of selection effects. I apply this methodology to Bell Atlantic Corp. v. Twombly, whose effects have been subject to speculation and debate. I find that Twombly precipitated no significant change in dismissal rates, even after accounting for selection effects.

Productivity and Firm Selection: Quantifying the 'New' Gains from Trade

We discuss how standard computable equilibrium models of trade policy can be enriched with selection effects. This is achieved by estimating and simulating a partial equilibrium model that accounts for a number of real world effects of trade liberalization: richer availability of product varieties; tougher competition and weaker market power of firms; better exploitation of economies of scale; and, of course, efficiency gains via firms selection. The model is estimated on EU data and then simulated in counter-factual scenarios. Gains from trade are much larger in the presence of selection effects with substantial variability across countries and sectors.

Productivity and Firm Selection: Quantifying the ‘New’ Gains from Trade

We discuss how standard computable equilibrium models of trade policy can be enriched with selection effects. This is achieved by estimating and simulating a partial equilibrium model that accounts for a number of real world effects of trade liberalisation: richer availability of product varieties; tougher competition and weaker market power of firms; better exploitation of economies of scale; and, of course, efficiency gains via firms selection. The model is estimated on EU data and then simulated in counterfactual scenarios. Gains from trade are much larger in the presence of selection effects with substantial variability across countries and sectors.

The Problem of Measuring Legal Change, with Application to Bell Atlantic v. Twombly

Measuring legal change - i.e., change in the way that judges decide cases - presents a vexing problem. In response to a change in the behavior of courts, plaintiffs and defendants will change their patterns of filing and settling cases. Priest and Klein's (1984) selection model predicts that no matter how favorable or unfavorable the legal standard is to plaintiffs, the rate at which plaintiffs prevail in litigation will not predictably change; thus, legal change cannot be measured with data on court outcomes. In this paper, I extend the selection model to develop a methodology for measuring legal change, even in the presence of selection effects. I apply this methodology to a recent, high profile Supreme Court case, Bell Atlantic Corp. v. Twombly. My model generates novel predictions, which are confirmed in the data, and I find that Twombly caused no legal change, even after accounting for possible selection effects.

Gender Wage Differentials among Disabled People : Evidence from South Korea

Empirical analysis for the comparison of gender differences among disabled people has been relatively neglected in the literature on discrimination. This paper using data from the 2008 PSED investigates gender wage differentials among the disabled in Korea. The selectivity corrected decomposition framework is employed to examine what factors - endowments, discrimination, and selectivity - account for the wage gap. The main results presented in this paper are as follows: First, the gender wage gap among the disabled is sizable. Second, the wage gap is significantly attributable to discrimination. Moreover, disabled female workers also suffer a substantial wage penalty in terms of the portion of their wages attributable to discrimination. Third, the endowments factor plays an important role in explaining gender wage differentials as well. Finally, the presence of selection effects raises the observed wage gap. Such evidence suggests that Korean disabled female workers are more likely to be disadvantaged than their male counterparts in terms of wages. Thus, national policies, regulations or laws against gender discrimination (e.g., the U.K. DDA 1995, the U.S. ADA of 1990) and additional supports beyond prohibiting discrimination (e.g., vocational training, on-the-job training) are needed to enhance the labor market status of disabled female workers in Korea.

The Role of the UN in International Crisis Termination, 1945-1994

Assessing the efficacy of UN involvement in intemational crises may be made more difficult by the presence of selectioneffects. Selection effects introduce a sample bias that thwarts objective empirical assessment. The UN may onlyselect easy or inexpensive crises or it may select the most severe and intractable crises. To compensate for selectioneffects, I employ a Heckman model to test for the detem1inants of successful UN crisis abatement. In addition toovercoming selection effects, the Heckman method also simulates a realistic sequential decision process. The firststep of the process models the initial UN decision to enter into a crisis. The second step models the detenninants ofsuccess after censoring crises in which the UN did not become involved. Failing to model the two steps as nonindependentprocesses can produce inconsistent, non-reliable and biased estimates in the second equation. I estimatejointly the UN decision to become involved in a crisis and the effectiveness of that involvement. Observations areinternational crises from 1945 to 1994 identified by the lntemational Crisis Behavior (ICB) data set. UNinvolvement is largely a positive function of the duration of the crisis, crisis gravity, and the number of actorsinvolved. UN success is a positive fimction of mediation, calls for action, emergency forces, and observers. Crisisviolence undennines success. I discuss findings that suggest the factors that get the UN involved actually make itharder to achieve success.