10,927 research outputs found
Modeling left-truncated and right-censored survival data with longitudinal covariates
There is a surge in medical follow-up studies that include longitudinal
covariates in the modeling of survival data. So far, the focus has been largely
on right-censored survival data. We consider survival data that are subject to
both left truncation and right censoring. Left truncation is well known to
produce biased sample. The sampling bias issue has been resolved in the
literature for the case which involves baseline or time-varying covariates that
are observable. The problem remains open, however, for the important case where
longitudinal covariates are present in survival models. A joint likelihood
approach has been shown in the literature to provide an effective way to
overcome those difficulties for right-censored data, but this approach faces
substantial additional challenges in the presence of left truncation. Here we
thus propose an alternative likelihood to overcome these difficulties and show
that the regression coefficient in the survival component can be estimated
unbiasedly and efficiently. Issues about the bias for the longitudinal
component are discussed. The new approach is illustrated numerically through
simulations and data from a multi-center AIDS cohort study.Comment: Published in at http://dx.doi.org/10.1214/12-AOS996 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Wave dynamics of a six-dimensional black hole localized on a tensional three-brane
We study the quasinormal modes and the late-time tail behavior of scalar
perturbation in the background of a black hole localized on a tensional
three-brane in a world with two large extra dimensions. We find that finite
brane tension modifies the standard results in the wave dynamics for the case
of a black hole on a brane with completely negligible tension. We argue that
the wave dynamics contains the imprint of the extra dimensions.Comment: revised version, 10 pages, 1 table and 2 figures. Accepted for
publication in Phys. Lett.
Relating Friedmann equation to Cardy formula in universes with cosmological constant
A relation between the Friedmann equation and the Cardy formula has been
found for de Sitter closed and Anti de Sitter flat universes. For the remaining
(Anti) de Sitter universes the arguments fail, and we speculate whether the
general philosophy of holography can be satisfied in such contents.Comment: 11 pages, Latex file, References added. New version to be published
in Phys. Lett.
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