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PubMed1982

Induction of aryl hydrocarbon hydroxylase activity in cell cultures by aroclors, residues from yusho oil samples, and polychlorinated biphenyl residues from fish samples.

Four Aroclor reference materials, cleaned-up extracts of 2 yusho rice oil samples, and cleaned-up extracts of 3 fish samples containing polychlorinated biphenyl (PCB) residues were tested for their ability to induce aryl hydrocarbon hydroxylase (AHH) activity in a rat hepatoma cell line. Before the AHH bioassay, the samples were fractionated by a Florisil column chromatographic method. All samples contained about 1000 micrograms PCBs before Florisil column chromatography. The first Florisil eluate contains about 95% of the PCBs in a typical Aroclor, and the second contains the more polar or adsorbent PCB congeners. In this study, the first eluate for all samples produced no quantifiable AHH activity. The second Florisil eluates of both Aroclors 1242 and 1248 induced AHH activity, whereas these eluates of both Aroclors 1254 and 1260 did not. This difference may be due to the presence in Aroclors 1242 and 1248 of 3,3',4,4'-tetrachlorobiphenyl, which has not been detected in Aroclors 1254 and 1260. The second Florisil eluates of the fish samples induced somewhat less AHH activity than did Aroclor 1242 or 1248. The second Florisil eluates of the PCB residues from yusho rice oil samples induced significantly greater AHH activity than these eluates of either Aroclor 1242 or 1248, perhaps because yusho rice oil contains a greater amount of polychlorinated dibenzofurans than PCB commercial mixtures on a PCB equivalent basis.

Animals↗
PubMed2004

Incorporating the sampling variation of the disease prevalence when calculating the sample size in a study to determine the diagnostic accuracy of a test.

During the design stage of a study to assess the population sensitivity (P(S)) (or specificity) of a diagnostic test, the number of subjects (N) who will be administered both a gold standard test and a new test needs to be calculated. A common approach is to calculate the number of cases (n) with a specific disease or condition as diagnosed by the gold standard test first, and then to determine N based on the prevalence or incidence rate of the disease (P(P)) in the population, calculated as N=n/P(P). Due to sampling variation, given the sample size N, the number of cases having the disease identified by the gold standard test could be less than N x P(P). In this case, the study would be under-powered and may fail to produce an unbiased and precise estimate. In this study, we investigated this possibility for a situation where the required sample size is calculated using the confidence interval approach. When the sampling variation is considered, the variance of the sample sensitivity is slightly inflated, but its confidence interval width becomes widely dispersed. In order to reach the originally designed precision, adjustment in the sample size, N, is needed and suggested in this paper.

Cross-Sectional Studies↗
PubMed2001

Sample size determination for equivalence test using rate ratio of sensitivity and specificity in paired sample data.

Before implementing a new diagnostic test, we may wish to study whether this test is noninferior to a reference test with respect to the sensitivity and/or the specificity. This paper discusses sample size determination for one-sided equivalence (or noninferiority) testing of the rate ratio using paired-sample data. Using large sample theory, this paper derives asymptotic sample size formulae for the required number of subjects giving a desired power 100(1 - beta)% at a specified alpha-level. To evaluate the accuracy of these formulae, this paper considers several test statistics and uses Monte Carlo simulation to estimate the corresponding type I error and power with the given resulting sample sizes in a variety of situations. Finally, this paper notes those situations for which the asymptotic sample size formulae developed here are of limited use and suggests a simple empirical adjustment to alleviate this limitation.

Controlled Clinical Trials as Topic↗
PubMed2005

A comment on sampling error in the standardized mean difference with unequal sample sizes: avoiding potential errors in meta-analytic and primary research.

The authors discuss potential confusion in conducting primary studies and meta-analyses on the basis of differences between groups. First, the authors show that a formula for the sampling error of the standardized mean difference (d) that is based on equal group sample sizes can produce substantially biased results if applied with markedly unequal group sizes. Second, the authors show that the same concerns are present when primary analyses or meta-analyses are conducted with point-biserial correlations, as the point-biserial correlation (r) is a transformation of d. Third, the authors examine the practice of correcting a point-biserial r for unequal sample sizes and note that such correction would also increase the sampling error of the corrected r. Correcting rs for unequal sample sizes, but using the standard formula for sampling error in uncorrected r, can result in bias. The authors offer a set of recommendations for conducting meta-analyses of group differences.

Humans↗
PubMed1997

Two-stage sampling for etiologic studies. Sample size and power.

Preexisting computerized databases are potentially valuable sources of epidemiologic data. Since such databases are infrequently created specifically for etiologic research, data may be available for the exposure of interest and, through record linkage, for the endpoint of interest, but lacking for potential confounders. Because of the size of these databases, two-stage sampling is an efficient alternative to surveying the entire study population for confounder data. At stage 1, information on exposure and disease status is obtained for the entire study population. Confounder data are collected for probability-selected subsamples at stage 2. Logistic regression is performed on the stage 2 samples, with the parameter estimates and variances appropriately corrected to account for the stage 1 data. In this paper, the authors present methods for determining the required stage 2 sample size in the case of categorical exposure and confounding variables. Sample size tables, power curves, and a computer program have been produced to accommodate a binary exposure and a single binary confounder. With the increasing availability of preexisting yet incomplete databases, the potential for use of two-stage sampling will greatly increase in the future. This investigation provides a basis for estimating the number of participants to sample for the collection of confounder data at the second stage.

Case-Control Studies↗
PubMed1990

Is probability sampling always better? A comparison of results from a quota and a probability sample survey.

Two surveys in the same defined population in Sydney's western suburbs in 1986 and 1987 provided the opportunity to compare results obtained from a quota and a probability sample survey. These surveys were designed to provide information for the planning of local health promotion programs. The quota sample survey was conducted in shopping centres and used quota sampling to select 1727 respondents. In the second survey, area probability sampling was used to select 484 respondents. This survey had a response rate of 65 per cent. There were 15 questions common to both surveys; results of only three differed significantly (p less than 0.05) between surveys. None of these differences was important from a public health perspective. The agreement between the results of these two surveys probably reflects the fact that the same selection bias has operated in both. Unless a very high response rate can be achieved, quota sample surveys with age and sex quota controls may be an acceptable alternative to probability sample surveys for gathering local data relevant to the development of health programs.

Adult↗
PubMed2004

Jugular venous sampling: an alternative to petrosal sinus sampling for the diagnostic evaluation of adrenocorticotropic hormone-dependent Cushing's syndrome.

Bilateral sampling of the inferior petrosal sinuses (IPSS) to distinguish Cushing's disease from the ectopic ACTH syndrome is accurate but risky and technically difficult. Bilateral sampling of the internal jugular vein (JVS) is simpler and presumably safer. To compare jugular and petrosal sinus venous sampling for distinguishing Cushing's disease from ectopic ACTH syndrome, we studied 74 patients with surgically proven Cushing's disease, 11 with surgically confirmed, and three with occult ectopic ACTH secretion. Patients underwent JVS and IPSS with administration of CRH on separate days. Ratios of central-to-peripheral ACTH in venous samples were calculated. At 100% specificity, IPSS correctly identified 61 of 65 patients with Cushing's disease [sensitivity, 94%; confidence interval (CI), 84-98%]. When patients with abnormal venous drainage were excluded, sensitivity was 98% (CI, 90-100%). JVS had a sensitivity of 83% (CI, 71-91%) at 100% specificity. Receiver operated characteristics plot areas under the curve were similar (0.968 +/- 0.020 and 0.974 +/- 0.016, area under the curve +/- se, JVS vs. IPSS). Although petrosal sampling had better diagnostic accuracy, CIs overlapped (95% CI, 90-100% vs. 86% CI, 78-94%). Centers with limited sampling experience may choose to use the simpler JVS and refer patients for IPSS when the results are negative.

ACTH Syndrome, Ectopic↗
PubMed2006

International intercomparison of retrospective luminescence dosimetry method: sampling and distribution of the brick samples from Dolon' village, Kazakhstan.

There are still many differences in dose estimates depending on the applied methods of retrospective dosimetry in the areas, which were affected by nuclear tests at the Semipalatinsk nuclear test site (SNTS). In order to provide more correct estimation of radiation doses to population in proximity to the SNTS an International Intercomparison of Retrospective Luminescence Dosimetry (RLD) method had been proposed. It was suggested there be a comparison of the dose estimates for the brick samples from the buildings in the settlement, suffered following nuclear tests at the SNTS. With this purpose, during the September-October 2002 field mission, the team of specialists from Kazakhstan and Japan had collected four whole bricks for RLD International Intercomparison. Three buildings were selected as sampling locations in Dolon' village (Kazakhstan). The slices from these bricks were distributed between six laboratories in Finland, Germany, Japan, Russia, UK and USA for independent estimations by the RLD method of the accumulated dose of external irradiation. The descriptions of sampling, locations, data on geographical coordinates, dates of building construction, mode of cutting of samples for distribution, labeling, condition of transportation, order of the distribution of samples and information concerning 137Cs and 239+240Pu soil contamination density in the village and near sampling locations are presented in the paper.

Air Pollution, Indoor↗
PubMed1991

Lot quality assurance sampling: single- and double-sampling plans.

Lot quality assurance sampling (LQAS) was originally developed for industrial applications. This article discusses the extension of its application to a public health setting. When resources must be allocated to several communities based on whether or not each exceeds a target proportion of members with a characteristic, a sampling scenario arises which is different to the standard parameter estimation scenario. LQAS is an efficient procedure for sampling in this instance. Under certain conditions, double sampling may further enhance the efficiency of an LQAS plan. LQAS is discussed and illustrated by examples, and the theoretical foundations of single and double lot quality assurance sampling are presented. Examples of sample size and critical value tables are also presented.

HIV Seroprevalence↗
PubMed1989

Determination of sample sizes for epidemiological surveys using cluster sampling technique.

Cluster sampling often provides a convenient and low cost device, in epidemiological surveys. The sample size needed under cluster sampling is generally larger than that in an individual based scheme due to the intra-class correlation existing in a cluster. This intra-class correlation coefficient is usually not known and some assumptions or estimates are essential. The strengths and weaknesses of cluster sampling over other sampling plans are presented and briefly discussed in this paper with particular reference to leprosy control programmes. One particular model of multistage cluster sampling technique is suggested in the evaluation of a District level programme, which includes determining the effectiveness of Multi-Drug Therapy, monitoring efficiency of paramedical workers and estimating the incidence of leprosy.

Catchment Area, Health↗
PubMed1999

By the way, doctor. At my annual physical, I received cards to return to my doctor after collecting small samples of stool to test for fecal occult blood. I'm having trouble getting around to collecting these samples, because it is hard to get along without the motrin I take for back pain. The test materials instruct me to discontinue aspirin or NSAIDs and some foods for at least a week before collecting the samples. What should I do?

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Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1999

Effects of injector geometry and sample matrix on injection and sample loading in integrated capillary electrophoresis devices.

The double-T injector design employed in many microchip capillary electrophoresis devices allows for the formation of very small (50-500 pL) sample plugs for subsequent analysis on-chip. In this study, we show that sample plugs formed at the channel junction can be geometrically defined. The channel width and injector symmetry prove to be of great importance to good performance. A unique pushback of solvent into the side channels can be induced when the side channels have a very low resistance to flow, and this helps to better define the injected sample plug. Samples and running buffers of differing ionic strength (e.g., 10 mM KCl buffer and 20 mM KCl sample) can yield widely variable results in terms of plug shape and amount injected (variations of 1.5 to 10x). Applying bias voltages to all the intersecting channels aids in controlling the plug shape. However, when the ionic strengths of buffer and sample are not matched, the actual amount injected (up to 10x variations) can be inconsistent with the appearance of the plug formed in the injector (up to only 30 % variations). Operating at constant pH and ionic strength produced the most consistent results. This report examines the effects of altering the injector geometry and solution ionic strengths, and presents the results of using bias voltages to control plug formation. The observed results should provide a benchmark for modeling of the fluid dynamics in channel intersections.

Electrophoresis, Capillary↗
PubMed2005

Slurry sampling techniques for the determination of lead in Bangladeshi fish samples by electrothermal atomic absorption spectrometry with a metal tube atomizer.

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a metal tube atomizer has been applied to the determination of lead in Bangladeshi fish samples. The slurry sampling conditions, such as slurry stabilizing agent, slurry concentration, pyrolysis temperature for the slurried fish samples, particle size and ultrasonic agitation time, were optimized for electrothermal atomic absorption spectrometry with the Mo tube atomizer. Thiourea was used as the chemical modifier for the interference of matrix elements. The detection limit was 53 fg (3S/N). The determined amount of lead in Bangladeshi fish samples was consistent with those measured in the dissolved acid-digested samples. The advantages of the proposed methods are easy calibration, simplicity, low cost and rapid analysis.

Animals↗
PubMed2003

Quantitative and qualitative measure of intralaboratory two-dimensional protein gel reproducibility and the effects of sample preparation, sample load, and image analysis.

We investigate one approach to assess the quantitative variability in two-dimensional gel electrophoresis (2-DE) separations based on gel-to-gel variability, sample preparation variability, sample load differences, and the effect of automation on image analysis. We observe that 95% of spots present in three out of four replicate gels exhibit less than a 0.52 coefficient of variation (CV) in fluorescent stain intensity (% volume) for a single sample run on multiple gels. When four parallel sample preparations are performed, this value increases to 0.57. We do not observe any significant change in quantitative value for an increase or decrease in sample load of 30% when using appropriate image analysis variables. Increasing use of automation, while necessary in modern 2-DE experiments, does change the observed level of quantitative and qualitative variability among replicate gels. The number of spots that change qualitatively for a single sample run in parallel varies from a CV = 0.03 for fully manual analysis to CV = 0.20 for a fully automated analysis. We present a systematic method by which a single laboratory can measure gel-to-gel variability using only three gel runs.

Automation↗
PubMed2005

Determination of copper in powdered chocolate samples by slurry-sampling flame atomic-absorption spectrometry.

Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L(-1) hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L(-1) hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 microg g(-1) and precision, expressed as relative standard deviation (RSD), of 2.5% (n = 10) for a copper content of approximately 30 microg g(-1), using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 microg g(-1). The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison.

Cacao↗