How many operating rooms are needed to manage non-elective surgical cases? A Monte Carlo simulation study.

BackgroundPatients often wait to have urgent or emergency surgery. The number of operating rooms (ORs) needed to minimize waiting time while optimizing resources can be determined using queuing theory and computer simulation. We developed a computer program using Monte Carlo simulation to determine the number of ORs needed to minimize patient wait times while optimizing resources.MethodsWe used patient arrival data and surgical procedure length from our institution, a tertiary-care academic medical center that serves a large diverse population. With ~4800 patients/year requiring non-elective surgery, and mean procedure length 185 min (median 150 min) we determined the number of ORs needed during the day and evening (0600-2200) and during the night (2200-0600) that resulted in acceptable wait times.ResultsSimulation of 4 ORs at day/evening and 3 ORs at night resulted in median wait time = 0 min (mean = 19 min) for emergency cases requiring surgery within 2 h, with wait time at the 95th percentile = 109 min. Median wait time for urgent cases needing surgery within 8-12 h was 34 min (mean = 136 min), with wait time at the 95th percentile = 474 min. The effect of changes in surgical length and volume on wait times was determined with sensitivity analysis.ConclusionsMonte Carlo simulation can guide decisions on how to balance resources for elective and non-elective surgical procedures

Multi-objective optimal designs in comparative clinical trials with covariates: The reinforced doubly adaptive biased coin design

The present paper deals with the problem of allocating patients to two competing treatments in the presence of covariates or prognostic factors in order to achieve a good trade-off among ethical concerns, inferential precision and randomness in the treatment allocations. In particular we suggest a multipurpose design methodology that combines efficiency and ethical gain when the linear homoscedastic model with both treatment/covariate interactions and interactions among covariates is adopted. The ensuing compound optimal allocations of the treatments depend on the covariates and their distribution on the population of interest, as well as on the unknown parameters of the model. Therefore, we introduce the reinforced doubly adaptive biased coin design, namely a general class of covariate-adjusted response-adaptive procedures that includes both continuous and discontinuous randomization functions, aimed to target any desired allocation proportion. The properties of this proposal are described both theoretically and through simulations.Comment: Published in at http://dx.doi.org/10.1214/12-AOS1007 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

On the almost sure convergence of adaptive allocation procedures

In this paper, we provide some general convergence results for adaptive designs for treatment comparison, both in the absence and presence of covariates. In particular, we demonstrate the almost sure convergence of the treatment allocation proportion for a vast class of adaptive procedures, also including designs that have not been formally investigated but mainly explored through simulations, such as Atkinson's optimum biased coin design, Pocock and Simon's minimization method and some of its generalizations. Even if the large majority of the proposals in the literature rely on continuous allocation rules, our results allow to prove via a unique mathematical framework the convergence of adaptive allocation methods based on both continuous and discontinuous randomization functions. Although several examples of earlier works are included in order to enhance the applicability, our approach provides substantial insight for future suggestions, especially in the absence of a prefixed target and for designs characterized by sequences of allocation rules.Comment: Published at http://dx.doi.org/10.3150/13-BEJ591 in the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

The spin-orbit resonances of the Solar system: A mathematical treatment matching physical data

In the mathematical framework of a restricted, slightly dissipative spin-orbit model, we prove the existence of periodic orbits for astronomical parameter values corresponding to all satellites of the Solar system observed in exact spin-orbit resonance

From Citizenship to Custody: Unwed Fathers Abroad and at Home

The sex-based distinctions of the Immigration and Nationality Act (INA) have been remarkably resilient in the face of numerous equal protection challenges. In Miller v. Albright, Nguyen v. INS, and most recently United States v. Flores-Villar — collectively the citizenship transmission cases — the Supreme Court has upheld the constitutionality of the INA’s provisions that require unwed fathers, but not unwed mothers, to take a series of affirmative steps in order to transmit citizenship to their children born abroad. The conventional account of these citizenship transmission cases is that the Court upholds sex-based distinctions that would otherwise fail heightened scrutiny because the immigration and citizenship context in which they arise typically affords plenary power to Congress. This Article argues that the conventional account is incomplete. The citizenship transmission cases are not best understood as examples of immigration law exceptionalism. To the contrary, they are remarkably consistent with the Court’s treatment of unwed fathers and mothers in its equal protection jurisprudence generally. An in-depth comparison of the citizenship transmission cases with the Court’s decisions regarding the rights of unwed fathers in a variety of other legal contexts reveals a uniform picture of how the Court approaches parental roles in the absence of a marital union — the Court assumes that the absence of legal ties with the father at the time of his child’s birth results in his real absence for purposes of establishing both paternity and a father-child relationship. The corollary to the unwed father’s absence is the unwed mother’s presence — the unwed mother is presumed throughout these decisions to remain with the child. Underlying both the INA and the Court’s decisions endorsing the statute is therefore a consistent custody determination: the unwed mother, whether she is foreign or American, is understood to invariably retain custody over the child. This Article evaluates the potential consequences of making explicit the custody determination that is implicit in the Court’s citizenship transmission cases; uncovering the custody decision assumed by these rules, and assessing it on its own terms, provides reasons to question this recurring sex-based determination. This Article concludes by noting an important limitation of focusing on the gender-related aspects of the statute, namely the exclusion of any discussion concerning its citizenship-related repercussions