单变量多因素观察性资料主要影响因素的逐步筛选

目的探讨如何用单变量分析的一般线性模型(GLM-Univariate)方法筛选“单变量多因素观察性资料”的主要影响因素。方法以住院患者病案首页数据中住院费用的影响因素分析为例,比较逐步回归方法与GLM-Univari-ate方法的优劣。结果逐步回归方法可能导致的主要问题是庞杂的哑变量处理和计算结果对哑变量赋值方法的高度依赖性,且不能分析因素的整体效应。GLM-Univariate不仅能克服上述问题,而且可以通过方差分析表中各因素(协变量)的P值和效应值η2大小,逐步筛选出主要影响因素和协变量,并建立相应的回归方程。结论GLM-Univariate过程可以完成单变量多因素观察性资料主要影响因素的筛选,并能够分析因素之间和因素与协变量间的交互效应,较逐步回归方法更为适宜。     

The Analysis of Contingency Tables: From Chi-Squared Tests and Log-Linear Models to Models of Mixed Membership

The roots of the modern log-linear model approach to the analysis of cross-classified data in the form of multi-dimensional contingency tables can found in the work of S. N. Roy and his students in the 1950s at the University of North Carolina. These papers set the stage for two major sets of developments in the analysis of categorical data in the 1960s and 1970s. I describe some of these contributions, where they intersected and where they diverged in focus, and some subsequent advances, including the role of latent variables alternatives, mixed membership models, and methods for very large sparse categorical data arrays.     

Chemical characterization of chestnut cultivars from three consecutive years: Chemometrics and contribution for authentication

Four Castanea sativa Miller cultivars (Aveleira, Boaventura, Judia and Longal) belonging to the Protected Designation of Origin “Castanha da Terra Fria”, from the Northeast of Portugal, were selected in 2006, 2007 and 2008. Their nutritional, fatty acids, triacylglycerols and tocopherols profiles were evaluated. Water was the major component, followed by carbohydrates, protein and fat, with energetic values lower than 190 kcal/100 g of fresh fruit. Oleic, linoleic and palmitic were the major fatty acids, 1-oleoyl-2-linoleoyl-3-linoleoyl-sn-glycerol, 1-linoleoyl-2-linoleoyl-3-palmitoyl-sn-glycerol, 1-oleoyl-2-linoleoyl-3-oleoyl-sn-glycerol and 1-linoleoyl-2-oleoyl-3-palmitoyl-sn-glycerol were the prevalent triacylglycerols and γ-tocopherol was the most abundant tocopherol. In each parameter, differences between cultivars, harvest year and the possible cultivar × year interaction were screened through a two-way analysis of variance. Differences among cultivars have been attenuated by the variability among years, leading, in general, to a significant interaction effect, which resulted in a relative homogeneity regarding chemical parameters, showing that nutritional and chemical composition was influenced by seasonal variability. A stepwise linear discriminant model, based on 10 (α-tocopherol, γ-tocotrienol, LLL, OLLn, δ-tocopherol, γ-tocopherol, δ-tocotrienol, PLLn, protein and OOO) of the 38 initial evaluated variables was also established. The model allowed the complete discrimination of cultivars with overall sensibilities and specificities of 100%, for both original grouped data and leave-one-out cross-validation procedures. Furthermore, similar results were also obtained using only tocopherols data, showing their usefulness as a discriminant factor for chestnut cultivars.     

The epidemiology of community acquired bacteremic pneumonia, due to Streptococcus pneumoniae, in the Top End of the Northern Territory, Australia--over 22 years

Background

Diseases caused by Streptococcus pneumoniae continue to cause substantial morbidity and mortality throughout the world. Furthermore, detrimental outcomes are more pronounced in some populations—such as those living in third world poverty, and Indigenous people who live in developed nations.

Methods

This study describes the epidemiology of blood culture positive S. pneumoniae community-acquired pneumonia (CAP) in the Top End of the Northern Territory of Australia. Demographics, indigenous status, medical risk factors, serotype and outcomes were collected from adults presenting to hospital with blood culture positive S. pneumoniae CAP, from 1987 to 2008.

Results

We report 205 cases, with a median age of 40 years. The average overall incidence rate ratio was 10.3 for indigenous adults compared with non-indigenous adults. There was no statistical difference between incidence rates pre and post-23-valent pneumococcal polysaccharide vaccine (23vPPV) introduction. Serotypes in presenting cases were predominantly (84.7%) 23vPPV types. The whole-population logistic regression model identified significant adjusted relative risks: 95% CI, for age 45 and older 1.6: 1.1, 2.2, indigenous 5.9: 3.7, 9.5, diabetes 2.3: 1.6, 3.3, excess alcohol 4.8: 2.8, 8.3, smoking 2.7: 1.9, 3.7 with indigenous + excess alcohol 18.5: 17.3, 19.7 as predictive for bacteremic S. pneumoniae CAP presentation.

Conclusions

Our results suggest that, the national 23vPPV program appears to be under-utilized. An integrated Public Health approach vigorously targeting indigenous adolescents, before substances such as alcohol and smoking are habitual, together with increased vaccine coverage, will reduce the burden of pneumococcal disease in this population.     

Chewing behaviour and bolus formation during mastication of meat with different textures

During chewing, meat is mashed under compression and shear bite forces whilst saliva is incorporated. The resulting mixture is shaped into a cohesive bolus by agglomeration of small particles, and triggers a swallow. This study aimed to investigate the relationship between chewing behaviour and bolus formation of meat with different textures. Twenty-five consenting young adults participated in this study. Electromyographic activity was recorded from surface electrodes on the elevator muscles (masseter and temporalis) during mastication of cold beef. Two different textures (T(1): tough and dry; T(2): tender and juicy) were studied, and subjects were asked to chew the beef and then spit out the bolus either: (1) after a constant chewing period of 7s or (2) when the bolus was ready to be swallowed. Meat samples were weighed before and after chewing to determine weight changes due to saliva incorporation and the release of meat juice. Cutting tests were applied to measure the maximum shear force. The mechanical shear force was maximal for meat before chewing (T(1)=124 N/cm(2); T(2)=83 N/cm(2)) and decreased with increased chewing duration. Texture differences analysed from mechanical measurements remained significant even when the boli were ready for swallowing (T(1)=39 N/cm(2); T(2)=32 N/cm(2)); the toughest meat gave the toughest bolus. Muscular activity adapted to the texture of the meat as soon as chewing began, and remained constant over the observed chewing period. Mean muscular activity was higher during the chewing of tough meat than during the chewing of tender meat. As a consequence, by the time a bolus was ready to be swallowed, more saliva had been incorporated into the tough meat samples (mean weight increase: 36%) than the tender meat samples (mean weight increase: 30%).     

Overt sentence production in event-related fMRI

The use of syntactic structures on a sentence level is a unique human ability. Functional imaging studies have usually investigated syntax comprehension. However, language production may be performed by different neuronal resources. We have investigated syntax generation on a sentence level with functional magnetic resonance imaging (fMRI). BOLD contrast was measured while subjects articulated utterances aloud. In the active condition 'sentence generation' (SG), subjects had to produce subject verb object (SVO) sentences (e.g. "The child throws the ball") according to syntactically incomplete stimuli (e.g. "throw ball child") presented visually. In the control condition 'word reading' (WR), subjects had to read identical stimuli without completing the syntactic structure, while in a second control condition 'sentence reading' (SR), subjects had to read complete sentences. The semantic meaning of all expressions was obvious despite the syntactically incomplete structure in conditions SG and WR. In both contrasts, SG minus WR and SG minus SR, activation was mainly present in the left inferior frontal (BA 44/45) and medial frontal (BA 6) gyri, the superior parietal lobule (BA 7) and the right insula (BA 13). A region of interest analysis revealed significantly stronger left-dominant activation in BA 45 compared to BA 44. Our data illustrates the crucial involvement of the left BA 45 in syntactic encoding and is in line with more recent imaging and brain lesion data on syntax processing on a sentence level, emphasizing the involvement of a distributed left and right hemispheric network in syntax generation.     

Evolution of Functional Exercise Capacity in Lung Transplant Patients With and Without Bronchiolitis Obliterans Syndrome: A Longitudinal Case–Control Study

IntroductionBronchiolitis Obliterans Syndrome (BOS) is a debilitating disease with limited treatment options that threatens both the quality of life and long-term survival of lung transplant (LTx) recipients. This retrospective longitudinal case–control study was performed to compare the long-term functional evolution of LTx recipients with and without BOS.MethodsTwenty-four LTx recipients with BOS (BOS=Cases) and 24 without BOS (NON-BOS=Controls) were selected and individually matched according to age, gender, diagnosis and LTx characteristics. Measurements of 6-minute walking distance (6MWD), symptoms of dyspnea (BORG CR-10 scale), and comprehensive pulmonary function testing were performed before LTx and at annual follow-up assessments after LTx.ResultsPeak FEV₁ after LTx was similar in both groups [FEV₁ (% predicted) 101 ± 25 vs. 101 ± 31, p = 0.96] and BOS diagnosis in cases was established 3.6 ± 2.5 years after LTx. At the final follow-up assessment (6.5 ± 3.2 years after LTx) FEV₁ (% predicted) was 86 ± 34 in NON-BOS vs. 44 ± 17 in BOS (p < 0.001). Evolution of 6MWD was different between groups (group by time interaction: p = 0.002). Borg dyspnea scores were also significantly different between groups at the final evaluation (NON-BOS 3.3 ± 1.7 vs. BOS 5.0 ± 2.2; p = 0.024).ConclusionsWe observed gradual reductions in functional exercise capacity and increasing symptoms of dyspnea in patients who developed BOS after LTx. As such, prospective studies seem warranted to explore whether rehabilitative interventions might be useful to improve symptoms and slow down deterioration of exercise capacity in these patients from the onset of BOS.     

Effect of temperature on mortality during the six warmer months in Sydney, Australia, between 1993 and 2004

Studies of heat-related mortality have been predominantly based on analyses of underlying cause of death as the single indicator of a population's vulnerability to high temperatures. Examination of both underlying and associated causes of death could provide a more comprehensive understanding of the population at risk. This study analyzes the impact of high temperatures on mortality in Sydney, Australia, during the warmer six months (October-March) between 1993 and 2004, using the underlying and associated cause of death due to all-cause, circulatory, and respiratory disease. Some mortality datasets were also divided into two age groups, 0-64 and 65+. A generalized linear model assuming negative binomial distribution was constructed for the daily mortality counts using daily maximum temperature and hourly maximum concentrations of ozone (O₃) and particulate matter (PM₁₀) as covariates. With the air pollution terms in a model, the change in mortality was estimated to be between 4.5% and 12.1% for a 10 °C increase in maximum daily temperature, depending on mortality dataset. When air pollutants were removed from a model, the above mortality percentages changed by −1.1% to 0.9%. When both underlying and associated causes of death were considered, the effect remained the same or became lower. Maximum temperature has been found to have a significant effect on mortality in Sydney, with PM₁₀ and O₃ confounding the association.