Calibration methods for estimating quantiles

We propose a calibrated estimator of the quantiles of sample survey data and discuss the asymptotic theory behind it. This estimator is defined for any sampling design and uses the information available on J auxiliary variables. A simulation study based on a real population is used to compare the estimator with various methods proposed previously.     

铁矿石取制样标准的研究

铁矿石贸易中,品质检验结果是结算的主要依据之一。取制样工作对品质检验的影响至关重要,不同取制样标准之间的差异可能导致检验结果的差异。本文以ISO标准为主,并对比其他相关标准,对铁矿石的取样、制样标准进行了研究,以期发现其中的差异,供标准的使用者参考。     

海产品中汞的快速检测研究

本文建立了固体测汞仪测定海产品中汞含量的方法。样品通过热解使汞释放,通过金汞齐吸收汞蒸气,加热吹扫定量释放金汞齐吸收的汞,用冷原子吸收法测定。本方法采用土壤标准物质绘制标准曲线,方法回收率为81.3%-123%,相对标准偏差（n=10）为14.5%。采用本方法对鱼粉中汞进行测定,结果与微波消解-原子荧光光谱法测定结果基本一致,略高于电感耦合等离子体质谱法（ICP-MS）的测定结果。固体进样技术避免了汞在样品消解过程中的损失,节约了分析时间和成本。     

自动顶空进样—气相色谱法测定柠檬酸中溶剂残留

[目的]建立自动顶空进样—气相色谱法测定柠檬酸中5种溶剂残留的分析方法。[方法]样品用水溶解,自动顶空进样,氢火焰检测器（FID）检测,外标法定量。[结果]平均回收率为85%~101%,相对标准偏差（RSD）为1.7%~4.2%,二氯甲烷、氯仿、苯、三氯乙烯、二氧六环检出限（LOD）分别为2、1、0.05、1、8mg/kg。[结论]该方法简便、快速、灵敏、准确,适合柠檬酸中5种溶剂残留定性和定量测定。     

带未知异方差广义空间模型的有效估计

空间单元大小以及其它的经济特征上的差异,常常会导致空间异方差问题。本文给出了广义空间模型异方差问题的三种不同估计方法。第一种方法是将异方差形式参数化,来克服自由度的不足,使用ML估计进行实现。而针对异方差形式未知时,分别采用了基于2SLS的迭代GMM估计和更加直接的MCMC抽样方法加以解决,特别是MCMC方法表现得更加优美。蒙特卡罗模拟表明,给定异方差形式条件下, ML估计通过异方差参数化的方法依然可以获得较好的估计效果。而异方差形式未知的情况下,另外两种方法随着样本数的增大时也可以与ML的估计结果趋于一致。     

基于持续期依赖马尔可夫转换模型的我国股市泡沫研究

使用持续期依赖马尔可夫转换模型,通过Gibbs抽样估计方法,对上海股票市场是否存在泡沫进行研究。结果表明,我国股票市场具有明显的持续期依赖特征。给出上海股票市场在样本期间内各时刻处于有泡沫状态的概率,发现在样本期间内有三个时段存在泡沫的概率超过了50%。     

Collecting samples from online services: How to use screeners to improve data quality

Increasingly, marketing and consumer researchers rely on online data collection services. While actively-managed data collection services directly assist with the sampling process, minimally-managed data collection services, such as Amazon’s Mechanical Turk (MTurk), leave researchers solely responsible for recruiting, screening, cleaning, and evaluating responses. The research reported here proposes a 2 × 2 framework based on sampling goal and methodology for screening and evaluating the quality of online samples. By sampling goals, screeners can be categorized as selection, which involves matching the sample with the targeted population; or as accuracy, which involves ensuring that participants are appropriately attentive. By methodology, screeners can be categorized as direct, which screens individual responses; and as statistical, which provides quantitative signals of low quality. Multiple screeners for each of the four categories are compared across three MTurk samples, two actively-managed data collection samples (Qualtrics and Dynata), and a student sample. The results suggest the need for screening in every online sample, particularly for the MTurk samples, with the fewest supplier-provided filters. Recommendations are provided for researchers and journal reviewers that provide greater transparency with respect to sample practices.     

食品抽样检测的方法与技巧

食物是维持人们日常生活的基础,如果没有食物,人类的生命将受到严重威胁。新中国成立初期,由于自然的原因,食物极其短缺,很多人因此而丧失生命。改革开放以来,人们的温饱问题得到解决,但食品的安全问题成为一大社会问题,本文论述食品抽样检测的方法与技巧分析。     

南海东部海上原油检验取样方法研究

系统介绍了南海东部海上原油外输检验各种取样方法的特点,对不同工作条件下如何选择合适的取样方法提出了建议。作为公认的最好方法,自动管线取样在不能阻止轻组分严重流失的作业环境中,样品的密度测试结果会发生较大偏差,容易引起贸易中的货量争议。根据ASTM标准相关内容,提出使用＂固定间隔手工取样并立即测试＂的方法,有效地解决了这一问题。这在海上原油外输检验领域具有一定参考价值,在原油贸易中应该引起重视。     

A NOTE ON SAMPLING WITH AND WITHOUT REPLACEMENT

Upper bounds are given for the total variation distance between the distribution statistics of random samples with and without replacement from a finite set.