Goodness-of-fit tests for the frailty distribution in proportional hazards models with shared frailty.

Frailty models account for the clustering present in grouped event time data. A proportional hazards model with shared frailties expresses the hazard for each subject. Often a one-parameter gamma distribution is assumed for the frailties. The choice of a particular frailty distribution is, most of the time, based on the availability of software, rather than on the way it fits the data. In this paper we construct formal goodness-of-fit tests to test for gamma frailties. We construct a new class of frailty models that extend the gamma frailty model by using certain polynomial expansions that are orthogonal with respect to the gamma density. For this extended family we obtain an explicit expression for the marginal likelihood of the data. The order selection test is based on finding the best fitting model in such a series of expanded models. A bootstrap is used to obtain p-values for the tests. Simulations and data examples illustrate the test's performance.Gamma distribution; Goodness-of-fit test; Frailty model; Order selection test; Orthogonal polynomial;

Sequential Search with Incompletely Informed Consumers: Theory and Evidence from Retail Gasoline Markets

A large variety of markets, such as retail markets for gasoline or mortgage markets, are characterized by a small number of firms offering a fairly homogenous product at virtually the same cost, while consumers, being uninformed about this cost, sequentially search for low prices. The present paper provides a theoretical examination of this type of market, and confronts the theory with data on retail gasoline prices. We develop a sequential search model with incomplete information and characterize a perfect Bayesian equilibrium in which consumers follow simple reservation price strategies. Firms strategically exploit consumers being uninformed about their production cost, and set on average higher prices compared to the standard complete information model. Thus, consumer welfare is lower. Using data on the gasoline retail market in Vienna (Austria), we further argue that incomplete information is a necessary feature to explain observed gasoline prices within a sequential search framework.

Adoption as a Social Marker: Innovation Diffusion with Outgroup Aversion

Social identities are among the key factors driving behavior in complex societies. Signals of social identity are known to influence individual behaviors in the adoption of innovations. Yet the population-level consequences of identity signaling on the diffusion of innovations are largely unknown. Here we use both analytical and agent-based modeling to consider the spread of a beneficial innovation in a structured population in which there exist two groups who are averse to being mistaken for each other. We investigate the dynamics of adoption and consider the role of structural factors such as demographic skew and communication scale on population-level outcomes. We find that outgroup aversion can lead to adoption being delayed or suppressed in one group, and that population-wide underadoption is common. Comparing the two models, we find that differential adoption can arise due to structural constraints on information flow even in the absence of intrinsic between-group differences in adoption rates. Further, we find that patterns of polarization in adoption at both local and global scales depend on the details of demographic organization and the scale of communication. This research has particular relevance to widely beneficial but identity-relevant products and behaviors, such as green technologies, where overall levels of adoption determine the positive benefits that accrue to society at large.Comment: 26 pages, 10 figure

Pre-incubation of cell-free HIV-1 group M isolates with non-nucleoside reverse transcriptase inhibitors blocks subsequent viral replication in co-cultures of dendritic cells and T cells.

In order to study the inhibitory effect of various reverse transcriptase inhibitors (RTIs) on cell-free HIV, we adapted a recently described in vitro system, based on co-cultures of dendritic cells and resting CD4 T cells, modelling early target cells during sexual transmission. The compounds tested included the second-generation non-nucleoside RTI (NNRTI) TMC-120 (R147681, dapivirine) and TMC-125 (R165335, travertine), as well as the reference nucleoside RTI AZT (zidovudine), the nucleotide RTI PMPA (tenofovir) and the NNRTI UC-781. The virus strains included the reference strain HIV-1Ba-L and six primary isolates, representative of the HIV-1 group M pandemic. They all display the non-syncytium-inducing and CCR5 receptor-using (NSI/R5) phenotype, important in transmission. Cell-free virus was immobilized on a poly-L-lysine (PLL)-treated microwell plate and incubated with compound for 1 h. Afterwards, the compound was thoroughly washed away; target cells were added and cultured for 2 weeks, followed by an extended culture with highly susceptible mitogen-activated T cells. Viral production in the cultures was measured on supernatant with HIV antigen ELISA. Negative results were confirmed by showing absence of proviral DNA in the cells. TMC-120 and TMC-125 inhibited replication of HIV-1Ba-L with average EC50 values of 38 nM and 117 nM, respectively, whereas the EC50 of UC-781 was 517 nM. Complete suppression of virus and provirus was observed at compound concentrations of 100, 300 and 1000 nM, respectively. Inhibition of all primary isolates followed the same pattern as HIV-1Ba-L. In contrast, pre-treating the virus with the nucleotide RTI PMPA and AZT failed to inhibit infection even at a concentration of 100000 nM. These data clearly suggest that NNRTIs inactivate RT enzymatic activity of different viral clades (predominant in the epidemic) and might be proposed for further testing as a sterilizing microbicide worldwide

Investigation of Selected Aspects of Kokanee (\u3cem\u3eOnchorhynchus nerka\u3c/em\u3e) Ecology in Porcupine Reservoir, Utah, With Management Implications

Several aspects of kokanee (Onchorhynchus nerka) ecology were studied in the fluctuating, 80ha Porcupine Reservoir, Utah in order to determine optimum management strategies. In 1981, escapement was enumerated and estimates of egg deposition were made . An estimate of the resulting fry recruitment was also attempted and was successful up to the arrival of spring runoff. In 1982, escapement was enumerated and estimates of egg deposition were made, with subsequent estimates of egg deposition and percent survival to the advanced eyed stage. Age and growth rates were determined and survival rates estimated. Escapement for 1981 and 1982 was 5,463 and 7,113 kokanee, respectively, depositing an estimated 1,843,955 and 2,393,757 eggs, respectively._ The estimated fry recruitment to the reservoir for the 1981 spawning run was 57,000 fish up to the arrival of spring runoff and appeared to be only a fraction of the total number of fry in the river. From the 1982 spawning run, an estimated 2,265,507 eggs were actually deposited, of these an estimated 64.2% or 1,457,599 eggs were fertilized and survived to the advanced eyed stage. Kokanee growth rates were good. Fish mature and spawn at 34 months of age at an average total length of 364mm. Twelve month old kokanee average 124mm and 24 month old fish 257mm. The kokanee population continues to grow but at a decreasing rate and survival rates are declining. For every kokanee that estimated 8.2 progeny survived to spawn spawned in 1972, an in 1975 and for every spawning kokanee in 1979 an estimated 3.0 progeny survived to spawn in 1982. The kokanee is presently underharvested and appears to be at or near the carrying capacity of the reservoir. In order to acheive an optimum sustainable yield the spawning population should be reduced and maintained at approximately 2,000 fish ( 1,000 redds)

Bypassing Democracy: Why Domestic Human Rights NGOs in Stable Democracies Appeal to Multilateral Forums

Answering why domestic advocacy groups in democratic states choose to utilize international institutions as part of their activism is an important component in understanding how democracies are pressured to comply with human rights obligations. The international relations literature on the subject of why domestic advocacy groups pressure states to comply by using international forums has centered around activists in repressive countries or the ways in which “gatekeepers” in international civil society either help or block domestic groups’ concerns. There has been little focus on why domestic advocacy groups in highly democratic states make efforts to independently engage with international forums. This study provides an answer through an investigation of domestic human rights NGOs in three democracies – the United States of America, Canada, and Germany – and their submissions to the first round of country reviews at the United Nations’ Universal Periodic Review (UPR) from 2006. The study examines the mechanisms through which 24 domestic human rights NGOs across these three countries came to use the Universal Periodic Review. The findings show that advocacy organizations in democracies opt to use international forums based partially on strategic explanations. NGOs also explain the use of international forums based on norms of how activism for human rights ought to be carried out. Overall, the decision to use international forums can be readily made on the basis of marginal advantages as well as steered by group norms and identity easily. This is because engagement with the Universal Periodic Review is a low-cost form of activism. Low resource or highly local groups often decide to make use of international forums as low-cost opportunities and subsequently rationalize using international forums through either strategic or normative rationales or a combination of the two. Highly professionalized groups more frequently articulate means-ends paths through which reporting to the UPR can lead to increased compliance. Neither type of group relies solely on means-ends justifications or solely on norm-driven rationalizations. Each type of group can articulate comparative advantages of using the UPR, whether those advantages have borne fruit or not. Groups process the decision to use international forums under conditions of uncertainty and frequently when such new low-cost opportunities are made known to them they decide to participate first as part of an all-of-the-above approach to dealing with intractable human rights violations. There is no one path to reporting to the UPR, but rather pathways are chosen that are contingent on a group’s past decisions and experiences, the networks of groups they have chosen to work within, and how activists perceive the political environment