ESTIMATING CENTRAL TENDENCY FROM UNCENSORED TRACE LEVEL MEASUREMENTS1

ABSTRACT: The statistical analysis of data which have trace level measurements has traditionally been a two-step process in which data are first censored using criteria based on measurement precision, and then analyzed with statistical methods for censored data. The process might be more informative if data were left uncensored. In this paper, information loss attributable to censoring and measurement noise are assessed by comparing the sample mean and median of uncensored measurements with a log regression mean and median based on censored data. Measurements are derived from lognormal parent distributions which have random variability characteristic of trace level measurement. The relative performance of estimators used with error-free samples and with samples having measurement noise can be explained by differences between the probability distributions of parents and measurements. Measurement introduces bias and dispersion and transforms lognormal parent distributions toward greater symmetry. Estimates using uncensored data are less biased and more accurate than the log regression mean and median when censoring exceeds about 50 percent, and are not much worse at any fraction censored. For data with many (80 percent) results below the limit of detection, bias may be quite severe.     

水污染物排放总量控制与管理系统的研究

探讨了水污染物排放总量控制研究方法．建立了由总量控制指标体系──技术经济政策──技术规范──微机管理系统组咸的水污染物排放总量控制管理系统。     

浅析室内环境污染检测与控制

分析了室内环境污染的由来、危害及内容,提出了对室内环境污染进行检测与控制,指出对室内环境污染的一些防治对策,表明室内空气污染必将引起广泛的关注和重视.     

济南市机动车污染与控制措施研究

针对对机动车污染的现状进行分析，提出加强机动车污染源头的排放控制和建立在用机动车排放控制管理体系是控制济南市机动车污染的有效措施。     

中国化学品船有毒液体物质污水管理现状及对策

分析了中国化学品船在有毒液体物质污水管理方面存在的问题 ,针对性地提出了有关对策     

塔里木及其周边地区的控矿构造、成矿系列和找矿预测──大型、超大型矿床找矿预测之剖析

塔里木是与华北、杨子齐名的中国三大块体之一，是连接中亚与太平洋西岸（中国东部）的桥■，一直为世人所瞩目。作者认为，塔里木板块是在前震旦系结品基底的基础上，主体部分经历了古生代稳定的陆台，中、新生代陆内盆地的演化阶段；边缘部分经历了新元古代一古生代一小生代的陆完增生和相邻洋壳的消亡。在局部地区和某些阶段，由于地壳发展的不均衡，曾发牛过裂谷、裂陷柏和扭壳断裂带。依据这一构造认识划分了赋存于塔里木板块基底构造层、中间构造层、上都构造层、古生代裂谷系、中一新生代超壳断裂排、被动边缘和陆壳增生区小的成矿系列。其中，石油、天然气、钾盐、金刚石、铜、稀有金属、铅、铸和宝玉石等多种矿产均具有非常巨大的找矿潜力。     

炭素生产中的炭尘排放总量控制与重点点源管理

以建立量化控制指标和重点管理为手段，研究炭尘重点点源排放规律，从强化污染源管理入手实行全过程控制以实现污染物排放总量控制。     

浅谈地质灾害控制因素与安全对策

地质环境的恶化，造成各类地灾害不断发生，直接威胁着人民生命财产的安全，越来越受到党和政府高度重视。本文通过10年来地质灾害治理施工，并根据滑坡施工的控制因素及特点，摸索了一套行之有效的安全管理办法和措施，有效地遏制了地质灾害施工安全事故，收到比较明显的效果。     

HLA-A,B,C,DR typing and 17-OHP determination for second trimester prenatal diagnosis of 21-hydroxylase deficient CAH

In 18 families at risk for the HLA-linked, 21-hydroxylase deficient form of autosomal recessive congenital adrenal hyperplasia (CAH), prenatal diagnosis (PD) was performed using two methods: (1) HLA-A,B,C typing and in the latter 11 cases also DR typing of cultured amniotic fluid cells (AFC) using the standard microcytotoxicity assay, and (2) measurement of second trimester amniotic fluid 17-hydroxyprogesterone (17-OHP) concentration using gel chromatography and radioimmunoassay. The accuracy of the prenatal predictions was confirmed by postnatal HLA typing of umbilical cord blood lymphocytes and by clinical evaluation. In 16/18 families, both HLA typing of AFC and 17-OHP measurements proved informative for PD. The predictions of both methods were concordant in 14/16 families (88 per cent). In ten of these families, a normal fetus was predicted, and in four, an affected fetus; all pregnancies were carried to term and all predictions were confirmed postnatally. In 2/16 cases (12 per cent), however, the predictions were discordant: the prenatal HLA typing indicated an affected fetus, whereas the 17-OHP values predicted a normal fetus. Both pregnancies were continued and two healthy boys were delivered. The discordance proved to be due to a ‘missed’ HLA antigen in one case and to serologically cross-reactive HLA antigens in the second. Finally, in 2/18 cases, prenatal assessment of fetal genotype had to rely on HLA typing alone as 17-OHP measurement was not performed in one family and in the second family the 17-OHP values obtained were not informative due to inadvertent continuation of hormone therapy to the date of amniocentesis. In both cases, the HLA typing data accurately predicted a normal fetus. In conclusion, a combination of HLA typing of cultured AFC and 17-OHP measurements of amniotic fluid permits accurate prenatal diagnosis of CAH in most cases (88 per cent). In addition, the supplementary use of HLA-DR typing of AFC as presented here for the first time proved helpful in families with HLA-A.B homozygosity due to parental sharing of antigens and can be informative for identifying HLA-B/21-OH recombinant haplotypes.     

城市降雨径流污染及最佳治理方案探讨

城市降雨径流污染已经成为非点源污染的一个新亮点,随着城市工业废水和生活污水等点源治理力度的加大,城市降雨径流污染问题将越来越突出.文章系统阐述了城市降雨径流污染的过程、污染类型及来源、污染物特征,对各种具体的城市降雨径流污染控制与治理技术进行了总结,并着重介绍了城市降雨径流污染最佳管理措施,还提出了实施城市降雨径流污染治理的具体对策和指导思想.