Estimating conditional proportion curves by regression residuals

Researchers often derive a categorical outcome from an observed continuous measurement y. For example, human obesity status can be defined by the body mass index. They proceed to estimate the conditional proportion curve p(x) = P(y?c(x)|x) versus the covariate x by regular categorical data analysis. In doing so, they fail to fully use the rich information in the original continuous measurement. Researchers also face additional difficulties caused by the uncertainty of the cutoff c(x), which defines the categories. For example, some cutoff may cause artificial discontinuity or non‐smoothness in the conditional proportion curve p(x). We propose a fully nonparametric empirical estimator using the standardized regression residuals from the general location‐scale model y=m(x) + v(x)e for the original continuous measurement. We prove the consistency of the proposed estimator in regular settings. The proposed estimator has several attractive features: it readily provides estimates for alternative cutoff values, and easily accommodates the discontinuity in p(x) caused by special cutoff. Numerical examples demonstrate that our method has better performance in mean‐squared error than some alternative approaches. We also discuss a design‐adjusted version of the proposed estimators to accommodate survey designs. The proposed methods are applied to data on obesity measurements among female Hispanic Americans. This new approach can be applied to other epidemiological and socio‐economic research that needs to define population categories from underlying continuous measurements. Copyright © 2010 John Wiley & Sons, Ltd.     

A program to implement a search method for identification of clinical subgroups

A procedure for identifying subgroups that are homogeneous with respect to an outcome variable is described. The method, search partition analysis (SPAN), is formulated in terms of a numeric outcome variable y and a set of predictors, explanatory variables or risk factors x = x₁, x₂, …, x_p. The objective is to split observations into two groups by a binary partition, specified using Boolean expressions of the predictors, x , such that y is as homogeneous as possible in the resultant groups; uniformly ‘low’ in one and uniformly ‘high’ in the other. Subgroups within each of the two groups can be identified from the Boolean expressions. SPAN implements a search for the ‘best’ partition from among a class of regular Boolean expressions. Features of the method are described, including how to measure partition homogeneity, complexity penalizing, search strategies and subgroup definition and representation. The approach is illustrated with analyses of predictors of low birth weight and predictors of impaired glucose tolerance for screening purposes.     

不同煤种呼吸性粉尘与尘肺病患病风险的剂量-反应关系分析

目的 探讨无烟煤、烟煤、褐煤呼吸性粉尘与尘肺病累计患病率的剂量-反应关系,为科学制定职业卫生标准提供依据。方法 对9处国有煤矿采煤工人的接尘和尘肺病患病情况进行调查研究,以寿命表法分别计算出无烟煤、烟煤、褐煤呼尘累计接尘量对应的累计患病率,利用线性回归方程进行单侧区间统计控制,得到呼尘接触浓度限值。结果 9处煤矿共21 000名采煤工人纳入研究,其中无烟煤、烟煤、褐煤煤矿采煤工人尘肺病检出率分别为11.27%、21.32%、6.00%,平均接尘工龄为20.12、22.88、25.21年。无烟煤、烟煤、褐煤煤矿采煤工人呼尘累计接尘量与尘肺病累计患病率的剂量-反应关系分别为线性回归方程y=5.788x-16.043（R²=0.949）、y=5.679x-16.837（R²=0.904）、y=6.465x-19.573（R²=0.944）。当接尘30年尘肺累计患病率≤1%时,以安全系数为1.2计算,三者呼尘接触浓度限值分别为1.7、2.3、3.9 mg/m³。结论 不同煤种的尘肺病检出率、平均接尘工龄、呼尘接触浓度限值均不同,在煤尘累计接尘量相似情况下,煤的挥发分越低（含碳量越高）,累计患病率越高（无烟煤 > 烟煤 > 褐煤）。建议按照不同煤种分别制定国家职业卫生煤尘标准。     

Jointly modeling the relationship between longitudinal and survival data subject to left truncation with applications to cystic fibrosis

Numerous methods for joint analysis of longitudinal measures of a continuous outcome y and a time to event outcome T have recently been developed either to focus on the longitudinal data y while correcting for nonignorable dropout, to predict the survival outcome T using the longitudinal data y, or to examine the relationship between y and T. The motivating problem for our work is in joint modeling of the serial measurements of pulmonary function (FEV1% predicted) and survival in cystic fibrosis (CF) patients using registry data. Within the CF registry data, an additional complexity is that not all patients have been followed from birth; therefore, some patients have delayed entry into the study while others may have been missed completely, giving rise to a left truncated distribution. This paper shows in joint modeling situations where y and T are not independent, that it is necessary to account for this left truncation to obtain valid parameter estimates related to both survival and the longitudinal marker. We assume a linear random effects model for FEV1% predicted, where the random intercept and slope of FEV1% predicted, along with a specified transformation of the age at death follow a trivariate normal distribution. We develop an expectation‐maximization algorithm for maximum likelihood estimation of parameters, which takes left truncation and right censoring of survival times into account. The methods are illustrated using simulation studies and using data from CF patients in a registry followed at Rainbow Babies and Children's Hospital, Cleveland, OH. Copyright © 2012 John Wiley & Sons, Ltd.     

Regression of the Level of Different Heavy Metals to Size of Marine Organisms Harvested from the “Jiyeh” Oil Spill Zone of the Eastern Mediterranean Sea

This study aimed to establish a baseline data on regression of the levels of Lead (Pb), Nickel (Ni) and Vanadium (V) to specific size dimensions of selected marine organisms harvested from an oil spill zone of the Eastern Mediterranean Sea. Twenty samples of each of Siganus rivulatus, Mullets and oysters were collected from each of six harvest sites. A total of 1, 3, and 3 respective significant regression equations (p < 0.01) were established between Pb, Ni, V and specific size dimensions of the selected marine organisms. The significant correlation associated with the highest R ² value was obtained between the Pb (y) level and the width (x) of the Siganus rivulatus (y = −86.833x + 417.72). The other six statistically significant correlations were associated with lower values of R ² ranging between 0.338 and 0.380. This baseline data will be used in the future to evaluate the self-purification process of pollutants in different sizes of indicator-marine organisms in this part of the Mediterranean Sea.     

Occupational dimethylformamide exposure

Summary The relationship between the 8-h time-weighted average (TWA) intensity of exposure toN, N-dimethylformamide (DMF) vapor (with little possibility of skin contact with liquid DMF) and the subsequent excretion ofN-monomethylformamide (MMF) precursor in shift-end urine samples was examined in 116 workers exposed to DMF and 92 workers exposed to DMF in combination with toluene. Urinary MMF level was examined also in 42 non-exposed subjects. The TWA vapor concentration in breathing zone air of each worker was successfully measured by means of a recently developed diffusive sampler in which water was used as an absorbent. The examination of gas chromatographic (GC) conditions for MMF determination showed that the formation of MMF was not saturated when the injection port temperature was set at 200°C, reached a plateau at 250°C, and showed no additional increase at 300°C. There was a linear relationship between DMF in air and MMF in urine with a regression equation ofy =1.65x + 1.69 (r = 0.723,P<0.01), wherey is MMF (unit; mg/l, uncorrected for urine density) in urine andx is DMF (ppm) in air, when only those exposed to DMF were selected, and the injection port temperature was set at 250°C. From this equation, it was possible to estimate that about 10% of the DMF absorbed will be excreted into urine as the MMF precursor. The slope of the regression line was significantly smaller among those exposed to DMF and toluene in combination as compared with those with DMF exposure only.     

Carbon disulphide

Summary Carbon disulphide (CS₂), a reagent of rayon production, is known for its high toxic potential and has therefore been the subject of many clinical studies. The aims of the study presented here were to determine the effective exposure to CS₂ and to compare the validity of the different exposure indicators. Internal and external exposure to CS₂ was investigated in 362 male workers of a viscose factory. The CS₂ air concentrations measured through stationary air monitoring in five different work areas (n = 39) were compared with the values of active personal air monitoring (n = 51) and passive personal air monitoring (n = 352). In addition, in all investigations biological monitoring was carried out by measuring the 2-thio-1,3-thiazolidine-carboxylic acid (TTCA) excretion in urine. A significant correlation was found between the data for active and passive personal air sampling (y = 0.99, x + 0.31, r = 0.968). The results of the stationary measurements led, however, to values which were systematically too low. The validity of TTCA excretion in urine as a parameter of biological monitoring could for the first time be verified in a large sample of subjects. There was a linear correlation between TTCA values in the urine related to both volume and creatinine [y (TTCAmg/g creatinine) = 0.315 x (ml CS₂/m³ air) + 0.59] and the CSZ values in the air. Nevertheless, TTCA excretion proved to be dependent upon creatinine so that the excreted amounts related to creatinine described the individual exposure more exactly.     

Effects of mercury vapor exposure on neuromotor function in Chinese miners and smelters

Objectives Current risk assessment of elemental mercury vapor is based on the tremor toxicity. To clarify the neuromotor effects of occupational exposure to mercury vapor, hand tremor and postural sway were measured in 27 miners and smelters (i.e., exposed workers) and 52 unexposed subjects. Methods Urine samples were collected and total mercury and creatinine concentrations were determined. Data of the tremor and postural sway were analyzed using the fast Fourier transformation. Results The geometric means of the urinary mercury level (UHg) were 228 (range 22.6–4,577) μg/g creatinine for the exposed workers and 2.6 (1.0–17.4) μg/g creatinine for the unexposed subjects. Total tremor intensity and frequency-specific tremor intensities at 1–6 and 10–14 Hz were significantly larger in the exposed workers than in the unexposed subjects (P < 0.05), but they were not significantly related to the UHg among the exposed workers (P > 0.05). In contrast, there were no significant differences in any postural sway parameters between the above two groups (P > 0.05), but the transversal sway with eyes open was positively related to the UHg among the exposed workers in using multiple regression analysis (P < 0.05). Conclusions These findings suggest that postural sway, as well as hand tremor, may be affected by elemental mercury vapor exposure, but the former test seems to be less sensitive to mercury than the latter one.     

Positioning matrix of economic efficiency and complexity: a case study in a university hospital

At the end of 2010, the Federico II University Hospital in Naples, Italy, initiated a series of discussions aimed at designing and applying a positioning matrix to its departments. This analysis was developed to create a tool able to extract meaningful information both to increase knowledge about individual departments and to inform the choices of general management during strategic planning. The name given to this tool was the positioning matrix of economic efficiency and complexity. In the matrix, the x‐axis measures the ratio between revenues and costs, whereas the y‐axis measures the index of complexity, thus showing “profitability” while bearing in mind the complexity of activities. By using the positioning matrix, it was possible to conduct a critical analysis of the characteristics of the Federico II University Hospital and to extract useful information for general management to use during strategic planning at the end of 2010 when defining medium‐term objectives. Copyright © 2013 John Wiley & Sons, Ltd.     

Metallic mercury induced tremor in rabbits and mercury content of the central nervous system

Fukuda, K. (1971).Brit. J. industr. Med.,28, 308-311. Metallic mercury induced tremor in rabbits and mercury content of the central nervous system. Tremor induced by metallic mercury was experimentally produced in rabbits by intermittent exposure to mercury vapour (average concentration of 4·0 mg/m³ for 6 hr/day on 4 days/week for 13 successive weeks). Two of six male rabbits exposed developed fine tremor and clonus in the fore- and hind-legs after 13 weeks' exposure. Electromyographic records showed typical grouped voltages accompanying the clonus (amplitude 0·3 to 1·0 mV, duration 20 to 30 ms, frequency 14 to 15 per second).

Activation analysis of the central nervous system showed mercury levels ranging from 0·8 to 3·9 μg/g wet tissue. The concentration in the cerebellum, the tegmentum, and the thalamus was significantly higher than in the remaining structures. The relationship between the tremor and the mercury content of the central nervous system is discussed and a positive causal relationship is suggested.

     

Mineralization Kinetics of Chemicals in Soils in Relation to Environmental Conditions

The mineralization kinetics of the detergentn-dodecylbenzenesulfonate ([¹⁴C]LAS) and the plasticizer di(2-ethylhexyl)phthalate ([¹⁴C]DEHP) were studied in three fresh sampled soils of different type. Time series of¹⁴CO₂evolution were fitted with various linear and nonlinear models. The kinetics could be represented best by a 3/2-order function with linear adaptation and three parameters:x₁describing the gradient of the exponential part of the curve,x₂the lag phase, andx₃the last, asymptotic part. These parameters as well as the maximal degraded amounts (A) were correlated with various environmental conditions. For LAS,Awas similar in all three soils and was positively related to pH in two soils and to humidity in one soil (rendzina). The parametersx₁–x₃were positively influenced by soil humidity in all three soils. The degraded amountsA, expressed as percentage of added dose, were independent of initial concentration. BothAand the parametersx₁–x₃increased with increasing temperature. Degradation was negligible below 3°C. For DEHP, the degradation was much slower than that of LAS and was most rapid and most complete in the rendzina soil. Relative degradationAwas lower for higher initial application rates. Temperature influenced bothAand the lag phase. Degradation was not significant below 10°C.     

Bildung und Verfrachtung von Ozon und anderen Photooxidantien

Photochemical oxidants (O₃, PAN, HCHO) are the typical pollutants in photochemicalSmog. They can be formed as the result of the sunlight induced oxidation of precursor pollutants emitted into the atmosphere (NO_x, C_xH_y). Other important precursor substances and reactive intermediates are compounds of the organic hydroxyl group (-O-H, for instance the methoxy radical CH₃O), hydroxyl radical OH, hydroperoxy radical HO₂, and singlet oxygen O. For the production of photochemical oxidants in smog, especially ozone, NO_x primarily act as catalysator. But C_xH_y serve as “combustibles”. The quantities of the several formed photooxidants are mainly dependent on intensity and duration of daily sunshine, temperature, oxidant concentrations at the beginning of a build-up period, and on emission rates and concentrations of primary pollutants (NO, C_xH_y). Maximum mixing ratios of secundary pollutants often occur at certain distances downwind of primary pollutant sources, dependent on meteorological conditions (wind velocity, rel. humidity, etc.) and on rate constants for oxidant formation cycles. During the period of July 5 to 11, 1984, for instance, 6 kilometers SW from Zürich we found maximum ground-level mixing ratios of about 150 ppbv ozone, 4 ppbv PAN and 9 ppbv formaldehyde, that is 5 (ozone) to 10 (PAN) times above the supposed oxidant concentrations of unpolluted continental air. The increase in ozone in the late morning and early afternoon is accompanied by an increase in PAN and HCHO and by a decrease in NO_x. This shows that in this case HCHO originates from photochemical reactions rather than being emitted directly to the atmosphere from vehicles. At this episode aircraft observations of ozone at altitudes of 400 to 800 meters above ground and up to 100 kilometers far from Zürich show a continuous daily increase in the mixing ratio during the afternoon. From the beginning of the measuring period (July 5) with 50 ppbv it increased up to 80 ppbv (July 9). In the afternoon of the same 9th of July the maximum O₃ value of above 160 ppbv was reached 10 km downwind of Zürich.     

基于面到面泊松克里格方法的手足口病发病率空间分布降尺度研究

目的 运用面到面泊松克里格降尺度方法,对山东省2010年区（县）手足口病发病率进行降尺度插值,探究手足口病在乡镇尺度上的空间分布模式,为卫生部门更精准的制定防控措施和分配医疗资源提供参考依据。方法 收集2010年山东省108个区（县）的手足口病发病数,采用面到面泊松克里格方法进行降尺度插值,运用地理信息系统（GIS）对插值结果进行空间可视化,将区（县）发病率降尺度插值到乡镇发病率,得到乡镇发病率空间分布。结果 降尺度插值时,拟合的点尺度半方差方程的自相关距离（变程）为20.38 km,变程范围内发病率具有空间自相关性。区（县）手足口病发病率估计值和实际值散点图拟合函数为y=1.053 1x,R²=0.99,不同尺度之间发病率保持一致。结论 手足口病发病率在20.38 km范围内具有一定的空间自相关性。在某一地区暴发手足口病时,有关部门可重点针对暴发区20.38 km范围内的地区进行重点监控,着重分配治疗药物等医疗资源。面到面泊松克里格降尺度方法能够被有效地应用于手足口病的空间制图中,为公共健康发病率高分辨率制图提供了一种新的方法。     

Neuropsychological function in manganese alloy plant workers

Objectives The objective was to investigate potential nervous system effects of manganese (Mn) exposure in workers employed in manganese-alloy-producing plants.Methods One hundred male Mn alloy plant workers were compared with 100 age-matched referents. The subjects were examined with a comprehensive neuropsychological test battery. Exposure was assessed by measurement of Mn concentrations in the workroom air, blood and urine.Results The geometric mean (GM) concentration of inhalable Mn in workroom air was 301 g/m³. The GM concentration of Mn in whole blood (181 nmol/l vs 160 nmol/l) (P=0.002) and urine (0.9 nmol/mmol creatinine vs 0.4 nmol/mmol creatinine) (P<0.001) was higher among the exposed subjects than among the referents. The Mn-exposed subjects had increased postural tremor while conducting a visually guided tremor test (static steadiness test) compared with the referents (mean number of contacts 94 vs 59 (P= 0.001); duration of contacts (in seconds) 5.1 vs 3.5 (P=0.003)). The tremor had larger frequency dispersion, indicating that the tremor included a wider variety of frequencies, among the exposed subjects than among the referents, assessed by the TREMOR test system. Smoking habits (self-reported) influenced the tremor parameters significantly, the Mn-exposed smokers having more tremor than the non-smoking Mn-exposed subjects. No differences between the groups were found in tests for cognitive functions, reaction time or in symptom reporting.Conclusion The Mn-exposed subjects had increased hand tremor compared with their referents. The tremor was related to exposure parameters. Smoking habits (self-reported) influenced the tremor parameters.     

Can public health researchers effectively communicate their findings? An evaluation of graph use at the 2006 European Conference on Public Health

Aim

To evaluate how researchers in the field of Public Health (PH) use graphical representations in the context of a scientific meeting.

Subjects and methods

We evaluated 159 graphs contained in the oral presentations given at the 2006 European Conference on Public Health. An ad-hoc data extraction form was developed on the basis of the available literature to evaluate type and characteristics of the graphs (e.g. format of axes, scales, legend, use of colours, presence of distortions). Principal component analysis (PCA) was performed to identify latent variables.

Results

We found that the majority of graphs were simple univariate displays such as bar diagrams (59.1%), and linear graphs (18.2%). Distortions were present in about 1 out of 3 graphs and they were less common in graphs made by researchers from northern and western European countries than in graphs made by researchers from other countries. Two factors emerged from PCA: clarity of the graph and appropriate use of colours.

Conclusion

The ability of PH researchers to fully exploit the visual potential of graphs appeared limited. Clarity and use of colours characterised use of graphics in oral presentations.

     

多导脑部磁刺激仪在辅助听觉记忆方面的研究

目的：检验多导脑部磁刺激仪的临床使用效果。方法：受试者16人，分为2组，第一组为对照组，使其在清醒状态下听取具有多信息点的新闻材料（听觉刺激），然后回答关于材料内容的答卷，最后采其脑电；第二组则是在清醒状态下接受经颅磁刺激的同时听取与前一组相同的新闻材料，在接受经颅磁刺激的同时答卷，最后进行采脑电工作。对两组答卷情况和脑电信号进行分析。结果：接受磁刺激组的答卷情况明显好于对照组，脑电信号的功率谱在前额部、颞部、顶部甚至全部脑区都有比对照组更强的兴奋性。结论：多导脑部磁刺激仪可以在一定程度上加强大脑的兴奋性．帮助人们更好地完成相应的工作．     

Experimental study on centerline velocities of a rectangular capture hood under realistic conditions

Capture hoods are an important component of a local ventilation system designed to reduce exposures to airborne contaminants. The velocity at any point along the centerline of the hood (V_x) is currently estimated using one of many predictive equations developed since the 1930s. It is unproven that those predictive equations for V_x are accurate, despite the prodigious number of studies concerning them. Among other issues, almost all experimental verifications were conducted for conditions that were either unrealistically ideal without competing air currents (e.g., zero cross draft) or were not described.

This study measured values of V_x along the midline using Particle Image Velocimetry (PIV) at distances of 1–14 inches in front of a rectangular capture hood. The experiments were conducted in a large wind tunnel (9′ × 12′ × 40′, H × W × L) using a heated, breathing, anthropomorphically sized manikin. Three 0 degree draft velocities (V_draft = 4, 14, and 50 ft/min) were tested, all directed toward the hood face and the back of the manikin (if present). For each value of V_draft, the velocity fields were measured in a factorial design with and without the manikin, and with and without a worktable underneath the hood. An ideal condition was represented by a freestanding hood at the 4 fpm draft. Nonideal conditions included the presence of a worktable or manikin, and the combination of table and manikin. Each condition was tested at the three levels of V_draft.

The experimental results found significant effects (p < 0.001) for V_draft, the presence of the manikin, the presence of the worktable, and all combinations of those factors. The effects of the independent variables were most pronounced at distances greater than 10 in (25.4 cm) from the hood face. It is concluded that none of the previously published models accurately predicted V_x under the realistic conditions tested in this study. A satisfactory model will have to include terms for V_draft and the presence of a worktable and a worker.     

The effects of some divalent metals on cardiac and branchial Ca-ATPase in a freshwater fish Saccobranchus fossilis

The heart and gill of a freshwater fish Saccobranchus fossilis have been shown to contain a Ca²⁺-activated ATPase involved in Ca²⁺ transport. Enzyme showed optimal activity at 3 mM Ca²⁺ and 3 mM ATP for gills and at 3 mM Ca²⁺ and 1 mM ATP for heart. Mg²⁺ was equally effective in stimulating enzyme activity but was not essential for hydrolysis. Maximum activity was found in heart ventricular muscles as compared to gills. Among all the metals tested Hg²⁺ was the most toxic (IC₅₀, 0.75 and 0.85 μM for heart and gill, respectively) followed by Pb²⁺, Mn²⁺, and Cd²⁺. The inhibition was concentration dependent and reached almost 100% with each metal at the highest concentration. Stimulation of enzyme activity was observed at lower concentrations of Mn²⁺ and Cd²⁺ but not with Pb²⁺ and Hg²⁺. Stimulation was more pronounced with Mn²⁺ than with Cd²⁺ in both heart and gills. The results indicated that the inhibitory effect of these metals might be through the Ca²⁺-ATPase which is a manifestation of the calcium pump in various tissues.     

Lethal and Sublethal Effects of Embryonic and Larval Exposure of Hyla versicolor to Stormwater Pond Sediments

Stormwater ponds are common features of modern stormwater management practices. Stormwater ponds often retain standing water for extended periods of time, develop vegetative characteristics similar to natural wetlands, and attract wildlife. However, because stormwater ponds are designed to capture pollutants, wildlife that utilize ponds might be exposed to pollutants and suffer toxicological effects. To investigate the toxicity of stormwater pond sediments to Hyla versicolor, an anuran commonly found using retention ponds for breeding, we exposed embryos and larvae to sediments in laboratory microcosms. Exposure to pond sediments reduced survival of embryos by ~50% but did not affect larval survival. Larvae exposed to stormwater pond sediment developed significantly faster ([`(x)] = 39 \bar{x} = 39 days compared to 42 days; p = 0.005) and were significantly larger at metamorphosis ([`(x)] =  0. 4 9 \bar{x} = \, 0. 4 9 g compared to 0.36 g; p < 0.001) than controls that were exposed to clean sand. Substantial amounts (712–2215 mg/l) of chloride leached from pond sediments into the water column of treatment microcosms; subsequently, survival of embryos was negatively correlated (r ² = 0.50; p < 0.001) with water conductivity during development. Our results, along with the limited number of other toxicological studies of stormwater ponds, suggest that road salt contributes to the degradation of stormwater pond habitat quality for amphibian reproduction and that future research should focus on understanding interactions among road salts and other pollutants and stressors characteristic of urban environments.     

The influence of location, source, and emission type in estimates of the human health benefits of reducing a ton of air pollution

The benefit per ton ($/ton) of reducing PM_2.5 varies by the location of the emission reduction, the type of source emitting the precursor, and the specific precursor controlled. This paper examines how each of these factors influences the magnitude of the $/ton estimate. We employ a reduced-form air quality model to predict changes in ambient PM_2.5 resulting from an array of emission control scenarios affecting 12 different combinations of sources emitting carbonaceous particles, NO _x , SO _x , NH₃, and volatile organic compounds. We perform this modeling for each of nine urban areas and one nationwide area. Upon modeling the air quality change, we then divide the total monetized health benefits by the PM_2.5 precursor emission reductions to generate $/ton metrics. The resulting $/ton estimates exhibit the greatest variability across certain precursors and sources such as area source SO _x , point source SO _x , and mobile source NH₃. Certain $/ton estimates, including mobile source NO _x , exhibit significant variability across urban areas. Reductions in carbonaceous particles generate the largest $/ton across all locations.