The use of Quantiles of Auxiliary Variables to Estimate Medians

This paper proposes the use of multi‐auxiliary information using quantiles and ratio and difference type estimators of the finite population distribution function to derive confidence intervals for medians. A simulation study based on three real populations compares its behaviour to that of standard methods.     

Multiple sensitive estimation and optimal sample size allocation in the item sum technique

For surveys of sensitive issues in life sciences, statistical procedures can be used to reduce nonresponse and social desirability response bias. Both of these phenomena provoke nonsampling errors that are difficult to deal with and can seriously flaw the validity of the analyses. The item sum technique (IST) is a very recent indirect questioning method derived from the item count technique that seeks to procure more reliable responses on quantitative items than direct questioning while preserving respondents' anonymity. This article addresses two important questions concerning the IST: (i) its implementation when two or more sensitive variables are investigated and efficient estimates of their unknown population means are required; (ii) the determination of the optimal sample size to achieve minimum variance estimates. These aspects are of great relevance for survey practitioners engaged in sensitive research and, to the best of our knowledge, were not studied so far. In this article, theoretical results for multiple estimation and optimal allocation are obtained under a generic sampling design and then particularized to simple random sampling and stratified sampling designs. Theoretical considerations are integrated with a number of simulation studies based on data from two real surveys and conducted to ascertain the efficiency gain derived from optimal allocation in different situations. One of the surveys concerns cannabis consumption among university students. Our findings highlight some methodological advances that can be obtained in life sciences IST surveys when optimal allocation is achieved.     

Characterization of entomopox virions of the army cutworm,Euxoa auxiliaris (Lepidoptera: Noctuidae)

Virions were released from virus-containing inclusions (VCI) of an entomopoxvirus of the army cutworm, Euxoa auxiliaris, with carbonate-thioglycolate solution. Knoblike projections present on the surface of the viral envelope were removed by digestion with trypsin. Trypsin-treated virions were homogeneous in both sucrose and CsCl gradients. The virions were similar to vertebrate poxviruses in morphology, contained 1.13 ± 0.3% DNA and had a buoyant density of 1.261 ± 0.003 gm/cm³ in CsCl. The virion preparations were infective and possessed RNA polymerase activity. Of eight species of Lepidoptera tested, only the species from which the virus was originally isolated proved susceptible to infection.     

Experimental laboratory infection of mosquito larvae with fungi of the genus Coelomomyces. II. Experiments with Coelomomyces punctatus in Anopheles quadrimaculatus

Experiments on the infection of Anopheles quadrimaculatus with Coelomomyces punctatus indicate that planonts released from sporangia are not infective for mosquito larvae but most likely infect the copepod Cyclops vernalis. Exposure of early-instar larvae to up to 5 × 10³ planonts per larva for as long as 48 hr resulted in no larval infections. Motile planonts were no longer detectable after 48 hr. However, incubation of early-instar larvae in media to which planonts, algae, and copepods had been added several days previously resulted in larval infection. Infection did not occur during the first 6 days after planont introduction. On day 7 and for several days thereafter, copepods were detected in the media which had an extensive mycelium developing in the hemocoel. This mycelium cleaved into thousands of posteriorly uniflagellate planonts. The presence of planonts at the time of mosquito infection, in conjunction with the above results, suggests that Cyclops vernalis is an alternate host for Coelomomyces punctatus and that the latter has a life cycle similar to that proposed for C. psorophorae involving a mosquito and a copepod as obligate alternate hosts. In established infection containers, dilution of the media with water significantly increased levels of infection 6 days later. All larval instars were susceptible to C. punctatus.     

‘无核白’葡萄及其营养变异系的光合作用与果实特性(英文)

以‘无核白’葡萄为对照,以其自然营养变异系‘长穗无核白’、‘长粒无核白’、‘大粒无核白’、‘W3’与‘W7’为材料,在新疆吐鲁番鄯善田间栽培条件下比较其果实及光合作用特性,为‘无核白’系列葡萄优良品种选育提供依据。结果表明:(1)供试各营养系具有较高的光、热利用能力,叶片日平均净光合速率(5.527 7~7.412 3μmol.m-2.s-1)均大于对照(4.879 7μmol.m-2.s-1);除‘长穗无核白’外,其余营养系均无明显光合‘午休’现象。(2)供试条件下净光合速率与田间空气温度、叶片温度、叶片表面蒸汽压差呈正相关;而气孔导度、光照强度等因子是‘无核白’系列葡萄光合作用的非决定因素。(3)‘长穗无核白’的穗长(36.43 cm)是对照(25.27 cm)的1.44倍;各营养系果粒均大于对照,其中‘W3’、‘大粒无核白’、‘长穗无核白’、‘长粒无核白’果粒(2.096 0、2.202 7、2.019 3、1.470 3 g)极显著大于对照(1.057 7 g)。(4)‘长粒无核白’果粒耐压力和果梗耐拉力均极显著优于对照,其他营养系与对照无显著差异;果粒较大的‘W3’、‘大粒无核白’、‘长粒无核白’等可溶性固形物含量(22.92%、23.57%、23.17%)与对照(23.85%)无差异。综合分析认为,供试营养系‘W3’、‘W7’和‘长粒无核白’相对较优良,宜进一步研究;研究证明果实与叶片光合作用特性指标可用于葡萄营养系选种。     

Estimating Incidence Rates from Population‐Based Case‐Control Studies in the Presence of Nonrespondents

In population‐based case‐control studies, it is of great public‐health importance to estimate the disease incidence rates associated with different levels of risk factors. This estimation is complicated by the fact that in such studies the selection probabilities for the cases and controls are unequal. A further complication arises when the subjects who are selected into the study do not participate (i.e. become nonrespondents) and nonrespondents differ systematically from respondents. In this paper, we show how to account for unequal selection probabilities as well as differential nonresponses in the incidence estimation. We use two logistic models, one relating the disease incidence rate to the risk factors, and one modelling the predictors that affect the nonresponse probability. After estimating the regression parameters in the nonresponse model, we estimate the regression parameters in the disease incidence model by a weighted estimating function that weights a respondent's contribution to the likelihood score function by the inverse of the product of his/her selection probability and his/her model‐predicted response probability. The resulting estimators of the regression parameters and the corresponding estimators of the incidence rates are shown to be consistent and asymptotically normal with easily estimated variances. Simulation results demonstrate that the asymptotic approximations are adequate for practical use and that failure to adjust for nonresponses could result in severe biases. An illustration with data from a cardiovascular study that motivated this work is presented.