A general hazard model for lifetime data in the presence of cure rate

Historically, the cure rate model has been used for modeling time-to-event data within which a significant proportion of patients are assumed to be cured of illnesses, including breast cancer, non-Hodgkin lymphoma, leukemia, prostate cancer, melanoma, and head and neck cancer. Perhaps the most popular type of cure rate model is the mixture model introduced by Berkson and Gage [1]. In this model, it is assumed that a certain proportion of the patients are cured, in the sense that they do not present the event of interest during a long period of time and can found to be immune to the cause of failure under study. In this paper, we propose a general hazard model which accommodates comprehensive families of cure rate models as particular cases, including the model proposed by Berkson and Gage. The maximum-likelihood-estimation procedure is discussed. A simulation study analyzes the coverage probabilities of the asymptotic confidence intervals for the parameters. A real data set on children exposed to HIV by vertical transmission illustrates the methodology.

Studies on mosquitoes (Diptera: Culicidae) and anthropic environment: 1- Parity of blood seeking Anopheles (Kerteszia) in South-Eastern Brazil

Populations of Anopheles (Kerteszia) were sampled fortnightly over a one-year period (August 1991 to July 1992) at Ribeira Valley, S. Paulo State, Brazil. Indoor and outdoor collections were made on human bait at evening crepuscular period. The Polovodova technique for age grading was applied to 3,501 females of Anopheles cruzii and to 416 females of An. bellator. That sample represented 34.4% of the total number of mosquitoes collected. The most abundant species found was An. cruzii. However, An. bellator showed an endophagy that was almost three times greater than that of An. cruzii. The overall parous rate was 25.4% and uniparity was practically dominant one. A proportion of 26.9% of An. cruzii and 12.0% of An. bellator were found to be uniparous. Only three outdoor females of the former species (0.1%) showed biparity. Parity of An. cruzii was higher in females caught outdoors than in those caught indoors. Nevertheless, 497 nulliparous females examined (417 cruzii and 80 bellator) had ovaries that had advanced to Christophers and Mer stages III to V. These results imply that these females had already practised hematophagy. Relating these results to those from the parous females, a high statistical significance was found, leading to the conclusion that gonothophic discordance is a common pattern among these anophelines. Further, these results obtained with human bait catches strongly suggest that nearly 38.0% of these host-seeking females had already taken at least one previous blood-meal. So it is possible that enough time could thus be available for the plasmodian development in the vectors.

Design and performance of a novel low-density parity-check code for distributed video coding

Low-density parity-check (LDPC) codes are nowadays one of the hottest topics in coding theory, notably due to their advantages in terms of bit error rate performance and low complexity. In order to exploit the potential of the Wyner-Ziv coding paradigm, practical distributed video coding (DVC) schemes should use powerful error correcting codes with near-capacity performance. In this paper, new ways to design LDPC codes for the DVC paradigm are proposed and studied. The new LDPC solutions rely on merging parity-check nodes, which corresponds to reduce the number of rows in the parity-check matrix. This allows to change gracefully the compression ratio of the source (DCT coefficient bitplane) according to the correlation between the original and the side information. The proposed LDPC codes reach a good performance for a wide range of source correlations and achieve a better RD performance when compared to the popular turbo codes.

Estimation of infection rate in epidemic models with multiple populations

Dissertação para obtenção do Grau de Mestre em Matemática e Aplicações Especialização em Actuariado, Estatística e Investigação Operacional

How Were Conflicts of Interest Handled?

Conflicts of interest were potentially great but they were minimized by the great conviction from both Doctors and Health Ministry that something had to be done to improve data on perinatal health. To decrease the number of hospitals where deliveries took place, to concentrate doctors, nurses and equipment, to define staff and to acquire equipment and to train nurses and paediatricians was the way. One the point of view of cost-effectiveness, centralization of expensive technologies, and development of expertise concentrating cases in a same centre - Surgery, VLBW, etc- and lowering mortality rates and get better outcomes were clear health gains. In 1989 after the political decision of closing small maternities the committee return to villages and cities to explain to political local power and people, the decision, which kind of care they will have in the future, why and expected gains. Level I hospitals and Health Centers stop to have deliveries; Health Centers were given a great responsibility: the follow up of the most part of the normal pregnancies by GP. There was no economic pressure because the National Health Service is free, there are no economic incentives for obstetrical or neonatal care, hospitals are financed through ICD, hospital level is defined according to both delivery and newborn care. In 1989 the rule was “No results can be obtained without the interested and responsible participation of all – institutions and people”. At that time the emphasis was on training. There are geographic influences on regionalization for example for islands and inner and far geographic areas. Also we would like to emphasize the influence of demographics on regionalization. As birth rate continues to decrease the hospitals left open 20 years ago with more than 1500 deliveries have to be closed now because the number of deliveries decreased. It was much more difficult and unacceptable to close some few maternities now than 20 years ago. All the difference was that at that time reasons were explained and now it was a Minister order. Other fearful events are the opening of private hospitals, the lowering gross national income, the economic difficulties and financial problems.

Seasonality, parity rates and transmission indices of Mansonella ozzardi (Manson) (Nematoda: Onchocercidae) by Cerqueirellum argentiscutum (Shelley & Luna Dias) (Diptera: Simulidae) in a lower Solimões River community, Amazonas, Brazil

Mansonella ozzardi is transmitted by two dipterian families, Ceratopogonidae (midges) and Simuliidae (black flies). In Brazil, black flies are vectors for this filariasis until now. In this paper, we determined the seasonality, parity capacity and parasitic infection rate of Cerqueirellum argentiscutum. The work was carried out in the Porto Japão community, Lower Solimões River, Amazonas, Brazil. Results show that the black flies were more abundant during the rainy season (from December to May). The number of parous flies was higher in every sampling during the course of year. Monthly Biting Rate (MBR1 123742.00, MBR2 86701.50) was high, although Parasitic Infection Rate (PIR1 0.06, PIR2 0.08) and Annual Transmission Potential (ATP 7.25) were low in numbers.

Growth rate of a terra firme rain forest in Brazilian Amazonia over an eight-year period in response to logging

This paper deals with growth rates of trees > 5cm dbh over an eight-year period from 257 species at the Tapajós National Forest. The discussion is centred on the behaviour of the forest after logging. Permanent sample plots were established in 1981 and measured at the first time. The area was logged in 1982. Measurements after logging occurred in 1983, 1987 and 1989. Considering all species together, diameter increment was similar for both intensities of logging until five years after logging. Light-demanding species showed significantly higher growth rates than shade-tolerant species in the logged forest, with greater increment in the heavier treatment intensity. Commercial species also had higher growth rates in the heavier logged area, although those were significantly different only in the period from one to five years after logging. In the undisturbed forest, growth rates increased with increasing dbh size. At species level, growth rate varied between and within treatments, as well as between trees within species, depending mainly on degree of canopy opening. The logging favoured the growth of commercial species, chiefly the light-demanders. Therefore, if the same growth conditions continue being given, for example by silvicultural treatments, to those species of commercial interest, the forest would reach a stock available for harvesting around year 30 after logging. However, the high variation in increment rates indicates that an eight-year period is not sufficient to allow predictions on cutting cycles or polycyclic management systems for the study forest.

High strain rate constitutive modeling forhistorical structures subjected to blast loading

Doctoral Thesis Civil Engineering

The short and long-run determinants of the real exchange rate in Mexico

This paper explores the real exchange rate behavior in Mexico from 1960 until 2005. Since the empirical analysis reveals that the real exchange rate is not mean reverting, we propose that economic fundamental variables affect its evolution in the long-run. Therefore, based on equilibrium exchange rate paradigms, we propose a simple model of real exchange rate determination which includes the relative labor productivity, the real interest rates and the net foreign assets over a long period of time. Our analysis also considers the dynamic adjustment in response to shocks through impulse response functions derived from the multivariate VAR model.

Technical Appendix-3-Regime asymmetric STAR modeling and exchange rate reversion

The breakdown of the Bretton Woods system and the adoption of generalized oating exchange rates ushered in a new era of exchange rate volatility and uncer- tainty. This increased volatility lead economists to search for economic models able to describe observed exchange rate behavior. The present is a technical Appendix to Cerrato et al. (2009) and presents detailed simulations of the proposed methodology and additional empirical results.

Equilibrium Exchange Rate Determination and Multiple Structural Changes

The large appreciation and depreciation of the US dollar in the 1980s stimulated an important debate on the usefulness of unit root tests in the presence of structural breaks. In this paper, we propose a simple model to describe the evolution of the real exchange rate. We then propose a more general smooth transition (STR) function than has hitherto been employed, which is able to capture structural changes along the (long-run) equilibrium path, and show that this is consistent with our economic model. Our framework allows for a gradual adjustment between regimes and allows for under- and/or over-valued exchange rate adjustments. Using monthly and quarterly data for up to twenty OECD countries, we apply our methodology to investigate the univariate time series properties of CPI-based real exchange rates with both the U.S. dollar and German mark as the numeraire currencies. The empirical results show that, for more than half of the quarterly series, the evidence in favour of the stationarity of the real exchange rate was clearer in the sub-sample period post-1980.

Analyzing aggregate real exchange rate persistence through the lens of sectoral data

In this paper we analyze the persistence of aggregate real exchange rates (RERs) for a group of EU-15 countries by using sectoral data. The tight relation between aggregate and sectoral persistence recently investigated by Mayoral (2008) allows us to decompose aggregate RER persistence into the persistence of its different subcomponents. We show that the distribution of sectoral persistence is highly heterogeneous and very skewed to the right, and that a limited number of sectors are responsible for the high levels of persistence observed at the aggregate level. We use quantile regression to investigate whether the traditional theories proposed to account for the slow reversion to parity (lack of arbitrage due to nontradibilities or imperfect competition and price stickiness) are able to explain the behavior of the upper quantiles of sectoral persistence. We conclude that pricing to market in the intermediate goods sector together with price stickiness have more explanatory power than variables related to the tradability of the goods or their inputs.

Bionomics of Anopheles aquasalis Curry 1932, in Guaraí, state of Rio de Janeiro, southeastern Brazil: I. Seasonal distribution and parity rates

From a total of 12,721 anophelines collected in a lowland area in Guaraí, Rio de Janeiro, from November 1991 to October 1992, 99.7% (12,688) were Anopheles aquasalis. This species occurred throughout the year, but in higher numbers from April to September, when rainfall was low or moderate. The proportion of parous females in June was significantly higher than the annual rate. An. aquasalis was weakly attracted by a light-trap, and no significant differences in abundance were detected between nights with and without moonlight.

Evolutionary implications of a high selfing rate in the freshwater snail Lymnaea truncatula.

Self-compatible hermaphroditic organisms that mix self-fertilization and outcrossing are of great interest for investigating the evolution of mating systems. We investigate the evolution of selfing in Lymnaea truncatula, a self-compatible hermaphroditic freshwater snail. We first analyze the consequences of selfing in terms of genetic variability within and among populations and then investigate how these consequences along with the species ecology (harshness of the habitat and parasitism) might govern the evolution of selfing. Snails from 13 localities (classified as temporary or permanent depending on their water availability) were sampled in western Switzerland and genotyped for seven microsatellite loci. F(IS) (estimated on adults) and progeny array analyses (on hatchlings) provided similar selfing rate estimates of 80%. Populations presented a low polymorphism and were highly differentiated (F(ST) = 0.58). Although the reproductive assurance hypothesis would predict higher selfing rate in temporary populations, no difference in selfing level was observed between temporary and permanent populations. However, allelic richness and gene diversity declined in temporary habitats, presumably reflecting drift. Infection levels varied but were not simply related to either estimated population selfing rate or to differences in heterozygosity. These findings and the similar selfing rates estimated for hatchlings and adults suggest that within-population inbreeding depression is low in L. truncatula.

Rate and predictors of service disengagement in an epidemiological first-episode psychosis cohort.

OBJECTIVES: To assess the prevalence and predictors of service disengagement in a treated epidemiological cohort of first-episode psychosis (FEP) patients. METHODS: The Early Psychosis Prevention and Intervention Centre (EPPIC) in Australia admitted 786 FEP patients from January 1998 to December 2000. Treatment at EPPIC is scheduled for 18 months. Data were collected from patients' files using a standardized questionnaire. Seven hundred four files were available; 44 were excluded, because of a non-psychotic diagnosis at endpoint (n=43) or missing data on service disengagement (n=1). Rate of service disengagement was the outcome of interest, as well as pre-treatment, baseline, and treatment predictors of service disengagement, which were examined via Cox proportional hazards models. RESULTS: 154 patients (23.3%) disengaged from service. A past forensic history (Hazard ratio [HR]=1.69; 95%CI 1.17-2.45), lower severity of illness at baseline (HR=0.59; 95%CI 0.48-0.72), living without family at discharge (HR=1.75; 95%CI 1.22-2.50) and persistence of substance use disorder during treatment (HR=2.30; 95%CI 1.45-3.66) were significant predictors of disengagement from service. CONCLUSIONS: While engagement strategies are a core element in the treatment of first-episode psychosis, particular attention should be paid to these factors associated with disengagement. Involvement of the family in the treatment process, and focusing on reduction of substance use, need to be pursued in early intervention services.