A Re-analysis of Caries Rates in a Preventive Trial using Poisson Regression Models

The analysis of caries incidence in clinical trials has several challenging features: (1) The distribution of the number of caries onsets per patient is skewed, with the majority of patients having few or no cavities; (2) the number of surfaces at risk varies (i) over time and (ii) between patients, due to eruption and exfoliation patterns, dental diseases, and treatments ; (3) surfaces within a patient differ in their caries susceptibility, and (4) caries onsets within a patient are correlated due to shared host factors. Recent statistical developments in the area of correlated data analyses permit incorporation of some of these characteristics into the analyses. With Poisson regression models, the expected number of caries onsets can be related to the number of surfaces at risk, the time they have been at risk, and surface- and subject-specific explanatory variables. The parameter estimated in these models is an epidemiological measure of disease occurrence: the disease incidence rate (caries rate) or the rate of change from healthy (sound) to diseased (carious). Differences and ratios of these rates provide standard epidemiological measures of excess risk. To illustrate, Poisson regression models were used for exploratory analyses of the Ylivieska xylitol study.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67228/2/10.1177_00220345940730021401.pd

How does our motor system determine its learning rate?

Motor learning is driven by movement errors. The speed of learning can be quantified by the learning rate, which is the proportion of an error that is corrected for in the planning of the next movement. Previous studies have shown that the learning rate depends on the reliability of the error signal and on the uncertainty of the motor system’s own state. These dependences are in agreement with the predictions of the Kalman filter, which is a state estimator that can be used to determine the optimal learning rate for each movement such that the expected movement error is minimized. Here we test whether not only the average behaviour is optimal, as the previous studies showed, but if the learning rate is chosen optimally in every individual movement. Subjects made repeated movements to visual targets with their unseen hand. They received visual feedback about their endpoint error immediately after each movement. The reliability of these error-signals was varied across three conditions. The results are inconsistent with the predictions of the Kalman filter because correction for large errors in the beginning of a series of movements to a fixed target was not as fast as predicted and the learning rates for the extent and the direction of the movements did not differ in the way predicted by the Kalman filter. Instead, a simpler model that uses the same learning rate for all movements with the same error-signal reliability can explain the data. We conclude that our brain does not apply state estimation to determine the optimal planning correction for every individual movement, but it employs a simpler strategy of using a fixed learning rate for all movements with the same level of error-signal reliability

Buffalo, Bush Meat, and the Zoonotic Threat of Brucellosis in Botswana

Brucellosis is a zoonotic disease of global importance infecting humans, domestic animals, and wildlife. Little is known about the epidemiology and persistence of brucellosis in wildlife in Southern Africa, particularly in Botswana.Archived wildlife samples from Botswana (1995-2000) were screened with the Rose Bengal Test (RBT) and fluorescence polarization assay (FPA) and included the African buffalo (247), bushbuck (1), eland (5), elephant (25), gemsbok (1), giraffe (9), hartebeest (12), impala (171), kudu (27), red lechwe (10), reedbuck (1), rhino (2), springbok (5), steenbok (2), warthog (24), waterbuck (1), wildebeest (33), honey badger (1), lion (43), and zebra (21). Human case data were extracted from government annual health reports (1974-2006).Only buffalo (6%, 95% CI 3.04%-8.96%) and giraffe (11%, 95% CI 0-38.43%) were confirmed seropositive on both tests. Seropositive buffalo were widely distributed across the buffalo range where cattle density was low. Human infections were reported in low numbers with most infections (46%) occurring in children (<14 years old) and no cases were reported among people working in the agricultural sector.Low seroprevalence of brucellosis in Botswana buffalo in a previous study in 1974 and again in this survey suggests an endemic status of the disease in this species. Buffalo, a preferred source of bush meat, is utilized both legally and illegally in Botswana. Household meat processing practices can provide widespread pathogen exposure risk to family members and the community, identifying an important source of zoonotic pathogen transmission potential. Although brucellosis may be controlled in livestock populations, public health officials need to be alert to the possibility of human infections arising from the use of bush meat. This study illustrates the need for a unified approach in infectious disease research that includes consideration of both domestic and wildlife sources of infection in determining public health risks from zoonotic disease invasions

Fitting curves to human respiratory data

Records of gas flow during breathing are cyclical, with the cycles varying in duration. The shape of these cycles may change with the intensity of respiratory stimulation or the development of respiratory disease, but currently research is hampered by the lack of a fully satisfactory technique for determining the shape of a typical cycle. The approach adopted here is to replace the time series by a 'phase diagram', plotting the time integral of flow against flow itself. Principal curves are then fitted. These are curves 'through the middle of the data' which were introduced by Hastie and Stuetzle. The shapes of these curves are compared, either directly or after reconstructing an average cycle corresponding to each fitted curve. This has the advantage that the shape of the waveform is separated from the amplitude, and from the duration of the breath. A disadvantage is that periods of zero flow are lost, and the reconstructed average cycle may show irregularities at points near zero flow as a result. In practice, the methodology showed clear differences in shape between the protocols, gave reasonable average cycles and ordered the waveform shapes according to the hardness of breathing induced by the protocols

A model to search for birth probabilities of mammal populations using fertility data

A model was constructed to predict monthly birth probabilities using mammalian fertility data. We used a sample of 147 female capybaras (Hydrochoerus hydrochaeris) hunted on a farm on Marajó Island, Brazil. In the model each month was treated as a multinomial with six cells representing the six possible reproductive states (five months gestation). A hypothesis test was carried out to see whether a cosine curve would fit the birth probabilities. The results offer no support for a seasonal component (F2,9 = 1.84, P = 0.21), whereas results from a direct census do (F3,23 = 87.29, P < 0.01). Some hunting techniques were biased towards killing pregnant females (&#967;(2)1= 7.2, P< 0.01), thereby spreading reproduction throughout the year (F2,9 = 1.84, P = 0.21). The model remained a powerful predictive tool to be used with mammalian fertility data as long as the data are not biased towards pregnant females

A model to search for birth probabilities of mammal populations using fertility data

A model was constructed to predict monthly birth probabilities using mammalian fertility data. We used a sample of 147 female capybaras (Hydrochoerus hydrochaeris) hunted on a farm on Marajó Island, Brazil. In the model each month was treated as a multinomial with six cells representing the six possible reproductive states (five months gestation). A hypothesis test was carried out to see whether a cosine curve would fit the birth probabilities. The results offer no support for a seasonal component (F2,9 = 1.84, P = 0.21), whereas results from a direct census do (F3,23 = 87.29, P < 0.01). Some hunting techniques were biased towards killing pregnant females (χ(2)1= 7.2, P< 0.01), thereby spreading reproduction throughout the year (F2,9 = 1.84, P = 0.21). The model remained a powerful predictive tool to be used with mammalian fertility data as long as the data are not biased towards pregnant females

Mixture modelling for cluster analysis

Cluster analysis via a finite mixture model approach is considered. With this approach to clustering, the data can be partitioned into a specified number of clusters g by first fitting a mixture model with g components. An outright clustering of the data is then obtained by assigning an observation to the component to which it has the highest estimated posterior probability of belonging; that is, the ith cluster consists of those observations assigned to the ith component (i = 1,..., g). The focus is on the use of mixtures of normal components for the cluster analysis of data that can be regarded as being continuous. But attention is also given to the case of mixed data, where the observations consist of both continuous and discrete variables

Bases epidemiológicas do Fator Acidentário Previdenciário Epidemiological foundations of the Accident Insurance Factor

ANTECEDENTES: O Conselho Nacional de Previdência Social, por meio da Resolução No. 1.236 de 28/4/2004, aprovou uma nova metodologia para definição do valor das alíquotas de contribuição devidas por empresas para o financiamento de benefícios previdenciários relacionados aos riscos do trabalho. Esta metodologia baseia-se em um indicador denominado de Fator Acidentário Previdenciário, FAP, construído a partir do risco epidemiológico, estimado para cada ramo de atividade econômica. Como parte da sua estratégia de validação, o Ministério da Previdência Social decidiu pela avaliação da sua consistência epidemiológica. OBJETIVOS: Nesse estudo analisaram-se os propósitos, as fontes de informação, a natureza das medidas epidemiológicas empregadas e a metodologia da construção desse indicador, identificando-se as suas vantagens e limitações, aplicabilidade e impactos potenciais futuros. MÉTODOS: Análise documental da Resolução No. 1236 e do documento anexo. RESULTADOS: O FAP avança ao se pautar por critérios científicos transparentes que poderão permitir a redução das alíquotas quando houver efetiva melhoria das condições de trabalho, e conseqüentemente, da morbimortalidade entre trabalhadores. Supera as dificuldades relacionadas à definição e registro do nexo causal das doenças do trabalho ao considerá-las em sua totalidade, não se restringido às ocupacionais. Como prevê a redução de alíquotas com a melhoria das condições de saúde dos trabalhadores poderá contribuir para uma mais efetiva atuação dos empregadores na prevenção. CONCLUSÕES: É necessário o acompanhamento contínuo e sistemático da aplicação do FAP, com ampla participação da sociedade, revisando-o e ajustando-o aos diferentes cenários econômicos, sociais e de saúde do País, atentando-se para o seu impacto sobre a arrecadação e contas da Previdência Social.<br>BACKGROUND: The Brazilian National Social Insurance Counsel of the Ministry of Social Insurance approved the Resolution N. 1.236 of 28/4/2004 that defines a new methodology to assess the value of taxes to be paid by firms, for occupational health related insurance costs. This methodology utilizes the Accident Insurance Factor, (Fator Acidentário Previdenciário) FAP, based on relative risks estimated for each industry trade. As part of its validation strategy, the Social Insurance Ministry decided to evaluate the epidemiological consistency of FAP. OBJECTIVE: The FAP purposes, data sources, the nature of the overall methodology, its advantages and limitations are all discussed, as well as its applicability and potential future impact on the Social Insurance Ministry budget and on the workers' health and safety. METHODS: A documental analysis was conducted with the Resolution text and its attached essay. RESULTS: The FAP represents an advance because of its transparent scientific criteria that may allows reduction of taxes, when improvement in work conditions and the resulting decrease in diseases or injuries are observed. It also overcomes problems of definition and assessment of occupational causal relationships because overall diseases and injuries will be considered regardless of their causal relation to occupational exposures. Since taxes can be reduced as work and health conditions improve, it may contribute to a more effective participation of employers in prevention. CONCLUSIONS: It is necessary to systematically and continuously monitor the application of FAP, with extensive society participation, reviewing and adjusting it to the distinct economic, social and health scenarios in the country, considering its impact on the Social Insurance budget