1,983 research outputs found
Closed-Form Bayesian Inferences for the Logit Model via Polynomial Expansions
Articles in Marketing and choice literatures have demonstrated the need for
incorporating person-level heterogeneity into behavioral models (e.g., logit
models for multiple binary outcomes as studied here). However, the logit
likelihood extended with a population distribution of heterogeneity doesn't
yield closed-form inferences, and therefore numerical integration techniques
are relied upon (e.g., MCMC methods).
We present here an alternative, closed-form Bayesian inferences for the logit
model, which we obtain by approximating the logit likelihood via a polynomial
expansion, and then positing a distribution of heterogeneity from a flexible
family that is now conjugate and integrable. For problems where the response
coefficients are independent, choosing the Gamma distribution leads to rapidly
convergent closed-form expansions; if there are correlations among the
coefficients one can still obtain rapidly convergent closed-form expansions by
positing a distribution of heterogeneity from a Multivariate Gamma
distribution. The solution then comes from the moment generating function of
the Multivariate Gamma distribution or in general from the multivariate
heterogeneity distribution assumed.
Closed-form Bayesian inferences, derivatives (useful for elasticity
calculations), population distribution parameter estimates (useful for
summarization) and starting values (useful for complicated algorithms) are
hence directly available. Two simulation studies demonstrate the efficacy of
our approach.Comment: 30 pages, 2 figures, corrected some typos. Appears in Quantitative
Marketing and Economics vol 4 (2006), no. 2, 173--20
Peculiar Features of the Velocity Field of OB Associations and the Spiral Structure of the Galaxy
Some of the peculiar features of the periodic velocity-field structure for OB
associations can be explained by using the model of Roberts and Hausman (1984),
in which the behavior of a system of dense clouds is considered in a perturbed
potential. The absence of statistically significant variations in the azimuthal
velocity across the Carina arm, probably, results from its sharp increase
behind the shock front, which is easily blurred by distance errors. The
existence of a shock wave in the spiral arms and, at the same time, the
virtually free motion of OB associations in epicycles can be reconciled in the
model of particle clouds with a mean free path of 0.2-2 kpc. The velocity field
of OB associations exhibits two appreciable nonrandom deviations from an ideal
spiral pattern: a 0.5-kpc displacement of the Cygnus- and Carina-arm fragments
from one another and a weakening of the Perseus arm in quadrant III. However,
the identified fragments of the Carina, Cygnus, and Perseus arms do not belong
to any of the known types of spurs.Comment: 14 pages, 3 postscript figures, to be published in Astronomy Letter
Scaling up prevention programmes to reduce the sexual transmission of HIV in China
Background Since 2007, sex has been the major mode of HIV transmission in China, accounting for 75% of new infections in 2009. Reducing sexual transmission is a major challenge for China in controling the HIV epidemic
A panel analysis of UK industrial company failure
We examine the failure determinants for large quoted UK industrials using a panel data set
comprising 539 firms observed over the period 1988-93. The empirical design employs data
from company accounts and is based on Chamberlain’s conditional binomial logit model,
which allows for unobservable, firm-specific, time-invariant factors associated with failure
risk. We find a noticeable degree of heterogeneity across the sample companies. Our panel
results show that, after controlling for unobservables, lower liquidity measured by the quick
assets ratio, slower turnover proxied by the ratio of debtors turnover, and profitability were
linked to the higher risk of insolvency in the analysis period. The findings appear to support
the proposition that the current cash-flow considerations, rather than the future prospects of
the firm, determined company failures over the 1990s recession
Do people really want to be nudged towards healthy lifestyles?
This paper assesses Thaler and Sunstein’s claim that policies that nudge individuals towards healthy lifestyles promote the welfare of those individuals, as judged by themselves. I argue that Thaler and Sunstein switch between two different interpretations of that clause. One interpretation gives the clause a wide range of applicability, but drains it of its content as a repudiation of paternalism. The other interpretation makes it more meaningful to say that people want to make the choices they are being nudged towards, but applies to a much narrower range of cases than Thaler and Sunstein have in mind
What happens if you single out? An experiment
We present an experiment investigating the effects of singling out an individual on trust and trustworthiness. We find that (a) trustworthiness falls if there is a singled out subject; (b) non-singled out subjects discriminate against the singled out subject when they are not responsible of the distinct status of this person; (c) under a negative frame, the singled out subject returns significantly less; (d) under a positive frame, the singled out subject behaves bimodally, either selecting very low or very high return rates. Overall, singling out induces a negligible effect on trust but is potentially disruptive for trustworthiness
Empowerment or Engagement? Digital Health Technologies for Mental Healthcare
We argue that while digital health technologies (e.g. artificial intelligence, smartphones, and virtual reality) present significant opportunities for improving the delivery of healthcare, key concepts that are used to evaluate and understand their impact can obscure significant ethical issues related to patient engagement and experience. Specifically, we focus on the concept of empowerment and ask whether it is adequate for addressing some significant ethical concerns that relate to digital health technologies for mental healthcare. We frame these concerns using five key ethical principles for AI ethics (i.e. autonomy, beneficence, non-maleficence, justice, and explicability), which have their roots in the bioethical literature, in order to critically evaluate the role that digital health technologies will have in the future of digital healthcare
Kinematics, Abundances, and Origin of Brightest Cluster Galaxies
We present kinematic parameters and absorption line strengths for three
brightest cluster galaxies, NGC 6166, NGC 6173 and NGC 6086. We find that NGC
6166 has a velocity dispersion profile which rises beyond 20 arcsec from the
nucleus, with a halo velocity dispersion in excess of 400 km/s. All three
galaxies show a positive and constant h4 Hermite moment. The rising velocity
dispersion profile in NGC 6166 thus indicates an increasing mass-to-light
ratio. Rotation is low in all three galaxies, and NGC 6173 and NGC 6086 show
possible kinematically decoupled cores. All three galaxies have Mg2 gradients
similar to those found in normal bright ellipticals, which are not steep enough
to support simple dissipative collapse models, but these could be accompanied
by dissipationless mergers which would tend to dilute the abundance gradients.
The [Mg/Fe] ratios in NGC 6166 and NGC 6086 are higher than that in NGC 6173,
and if NGC 6173 is typical of normal bright ellipticals, this suggests that cDs
cannot form from late mergers of normal galaxies.Comment: 21 pages, accepted for publication in MNRA
Endogeneity in Panel Data Models with Time-Varying and Time-Fixed Regressors: To IV or Not IV?
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