复杂样本Horvitz-Thompson估计量的权数计算

目前国内进行的调查大都采用复杂抽样方案,但在分析时却常常采用只适用于简单随机样本的一般方法。本文论述了这样做可能产生的问题,同时介绍了用于复杂样本情形的Horvitz-Thom pson 估计量及改进的权数,并通过实例说明了计算方法及其合理性     

Determination of four metabolites of the plasticizer di (2-ethylhexyl) phthalate in human urine samples

Summary A method for biological monitoring of exposure to the plasticizer di(2-ethylhexyl)phthalate (DEHP) is described. In this method the four main metabolites of DEHP [i.e., mono (2-ethylhexyl) phthalate (MEHP), mono (5-carboxy-2-ethylpentyl)phthalate, mono(2-ethyl-5-oxohexyl)phthalate, and mono(2-ethyl-5-hydroxyhexyl)-phthalate] are determined in urine samples. The procedure includes enzymatic hydrolysis, ether extraction, and derivatization with triethyloxonium tetrafluoroborate. Analysis is performed by gas chromatography electron impact mass spectrometry. The detection limit for all four metabolites is less than 25 g/l urine. The coefficient of variation based on duplicate determinations of urine samples of workers occupationally exposed to DEHP was 16% for MEHP (mean concentration 0.157 mg/l) and 6% -9% for the other three metabolites (mean concentrations 0.130-0.175 mg/1). The method described here was used to study DEHP metabolism in man. Most persons excrete mono(2-ethyl-5-oxohexyl)-phthalate and mono (2-ethyl-5-hydroxyhexyl)phthalate as a (glucuronide) conjugate. Mono (5-carboxy-2-ethyl-pentyl)phthalate is mainly excreted in free form, while for MEHP a large interindividual variation in conjugation status was observed. Of the four metabolites quantified, 52% are products of a ((-l)-hydroxylation reaction of MEHP [i.e., mono (2-ethyl-5-oxohexyl)phthalate and mono (2-ethyl-5-hydroxyhexyl)phthalate], 22% is the product of a -hydroxylation reaction of MEHP [i.e., mono (5-carboxy-2-ethylpentyl)phthalate], and 26% is not oxidized further (i.e., MEHP). A good correlation is obtained when the amount of MEHP -hydroxylation products is compared with the amount of MEHP (-1)hydroxylation products in urine samples. When the internal dose of DEHP has to be established we recommend that the levels of all four metabolites of DEHP be studied in urine samples.     

30家餐饮业卫生状况调查分析

目的 :为了解我省餐饮业卫生状况 ,针对性制定管理对策。方法 :采取随机抽样的方法选取合肥市30家餐饮业进行了卫生学调查。结果 :大型餐饮业卫生管理组织和制度健全 ,有较完善的基础卫生设施 ,餐具消毒合格率高 (88.9% ) ,中、小型餐饮业卫生问题较多 ,是餐饮业卫生管理的薄弱环节。结论 :今后应加强对餐饮业的卫生监督与管理。     

Bayesian图解模型—直线回归

Bayesian图解模型是综合Bayesian理论,图论的观点及MCMC模拟方法的复合模型,现通过具体实例系统地介绍该模型的基本思想,建模求解及推论过程,体现Bayesian图解模型的优点与不足。     

二阶比估计

给出了二阶比估计量的偏差、估计量的均方误差以及均方误差的估计.     

Health-related quality of life in childhood disorders: A modified focus group technique to involve children

Objectives: Qualitative methodology has been under-utilized in child health research due to lack of a specific set of instruments. The objective of this study was to develop a child-centred qualitative research methodology to facilitate direct exploration of health-related quality of life (HRQL) issues and to identify the quality of life elements in pre-adolescent children with a chronic medical condition. Study Design: Purposeful stratified sampling of children, ages 6–12, who function in a regular school class, with active epilepsy who were assembled in small focus groups. The groups met in four phases and were led by moderators who probed preset open questions and activities. Results: The study demonstrated that our modified focus groups process was a powerful exploratory experience eliciting meaningful and important issues in quality of life beyond what parents and health professionals expected, and helped identify HRQL elements in childhood epilepsy. Conclusion: Modified focus groups are appropriate and suitable to explore quality of life issues in pre-adolescent children with a chronic medical condition. The process is feasible and trustworthy.     

Stratified case sampling and the use of family controls

We compare the asymptotic relative efficiency (ARE) of different study designs for estimating gene and gene-environment interaction effects using matched case-control data. In the sampling schemes considered, cases are selected differentially based on their family history of disease. Controls are selected either from unrelated subjects or from among the case's unaffected siblings and cousins. Parameters are estimated using weighted conditional logistic regression, where the likelihood contributions for each subject are weighted by the fraction of cases sampled sharing the same family history. Results showed that compared to random sampling, over-sampling cases with a positive family history increased the efficiency for estimating the main effect of a gene for sib-control designs (103-254% ARE) and decreased efficiency for cousin-control and population-control designs (68-94% ARE and 67-84% ARE, respectively). Population controls and random sampling of cases were most efficient for a recessive gene or a dominant gene with an relative risk less than 9. For estimating gene-environment interactions, over-sampling positive-family-history cases again led to increased efficiency using sib controls (111-180% ARE) and decreased efficiency using population controls (68-87% ARE). Using case-cousin pairs, the results differed based on the genetic model and the size of the interaction effect; biased sampling was only slightly more efficient than random sampling for large interaction effects under a dominant gene model (relative risk ratio = 8, 106% ARE). Overall, the most efficient study design for studying gene-environment interaction was the case-sib-control design with over-sampling of positive-family-history-cases.     

Comparison between 360° and 180° data sampling in thallium-201 rest-redistribution single-photon emission tomography to predict functional recovery after revascularization

Whether 360° or 180° imaging should be used in cardiac thallium-201 single-photon emission tomography (SPET) studies to detect coronary artery disease remains controversial. Moreover, the relative diagnostic accuracy of 360° and 180°²⁰¹Tl SPET for the assessment of myocardial viability has never previously been studied. The aim of this study was to perform a direct comparison between 180° and 360° data sampling to detect viable myocardium in patients undergoing revascularization; in order to allow optimal detection of viability a rest-redistribution protocol was used. The²⁰¹Tl results were compared with improvement of regional wall motion abnormalities after the revascularization, which was considered as the gold standard for myocardial viability. Thirty-two patients, scheduled for revascularization, underwent rest-redistribution²⁰¹Tl SPET, using a 360° arc. Raw data along a 180° arc (45° RAO to LPO) were selected from the original 360° data sets (both early an late²⁰¹Tl images). All SPET data were analysed semi-quantitatively using circumferential profiles of the short-axis images; the data were displayed in polar maps. Criteria for viability included percentage²⁰¹Tl redistribution and percentage²⁰¹Tl activity on the late image. Regional wall motion was assessed with two-dimensional echocardiography before and 3 months after revascularization. The sensitivities of 360° and 180° imaging for the prediction of functional recovery were 82% and 89%, respectively, whereas the specificities were 51% and 55%, respectively. The diagnostic accuracy of 360° imaging was 62% and that of 180° imaging 67%. This study shows that 360° and 180° imaging have comparable diagnostic accuracy in the prediction of functional recovery after revascularization. With the newer dual-head gamma camera systems with each detector opposing each other, 360° imaging may be preferred.     

The effect of irritant dermatitis on cutaneous bioavailability of a metronidazole formulation, investigated by microdialysis and dermatopharmacokinetic method

Background:  Determination of drug penetration in diseased skin represents a challenge.
Objective:  To compare dermal microdialysis and tape-strip sampling of drug penetration in normal skin and skin with irritant dermatitis.
Methods:  The two methodologies were employed simultaneously in 16 healthy volunteers. Samples were collected in a study of the penetration of a metronidazole cream formulation (Flagyl^® 1%) applied to forearm skin in both areas with irritant dermatitis and normal skin. Barrier perturbation and the depth of microdialysis probes were quantified by non-invasive bioengineering methods.
Results:  Microdialysis showed a significant threefold increase in metronidazole penetration in skin with irritant dermatitis compared with unmodified skin. Conversely, the concentration of metronidazole in tape-strip samples was significantly decreased in irritant dermatitis.
Conclusion:  The selection of sampling methodology should be based on the skin layer of interest as well as the integrity of the skin barrier. Whenever the dermal tissue is the target for topical treatment, microdialysis sampling should be the method of choice.     

Deposition of nickel, chromium, and cobalt on the skin in some occupations - assessment by acid wipe sampling

Background:  Nickel, chromium, and cobalt are important skin sensitizers. Better knowledge about skin exposure is needed for more efficient prevention. We have previously developed acid wipe sampling for assessment of skin exposure to metals.
Objectives:  To apply the acid wipe sampling technique in some occupations where intense contact with metallic items occurs and to gather experience for the design of future workplace studies.
Methods:  18 volunteers (carpenters, locksmiths, cashiers, and secretaries as controls) participated. They performed their normal tasks during a job session for exposure. Samples were taken from fingers and palms by acid wipe sampling, and analysis of metals was performed by inductively coupled plasma mass spectrometer.
Results:  The metals were detected in all samples, and the amount of nickel was larger than that of chromium and cobalt. Fingers were more exposed than palms. 8-h exposure to nickel was calculated and was highest in locksmiths (mean 3.784 μg/cm², range 1.846–5.028 μg/cm²) followed by carpenters, cashiers, and secretaries.
Conclusions:  The acid wipe sampling technique is suitable for studies of skin exposure to nickel, chromium, and cobalt in the workplace. The sampling efficiency of acid wipe sampling is high. The amounts of nickel deposited on skin in carpenters, locksmiths, and cashiers are judged capable of eliciting allergic contact dermatitis.