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PubMedDate not supplied

Sample stacking by acetonitrile-salt mixtures.

A new type of sample stacking for capillary zone electrophoresis (CZE), which occurs in mixtures of acetonitrile and high concentrations of inorganic salts in the sample, is described here. It is different from the stacking obtained in low-ionic-strength buffers in the sample since it is improved by the presence of a high concentration of ions while the latter type deteriorates in the presence of such ions. It is based on the addition of acetonitrile to the sample to eliminate proteins by precipitation. From a practical point of view, the stacking in acetonitrile is more useful since it both removes proteins and counteracts the deleterious effects of high concentrations of inorganic ions present in the sample. Furthermore, it allows a larger volume of the sample to be loaded on the capillary. More than one-third of the capillary can be loaded with the sample by this type of stacking, producing a high sample concentration with good resolution and increased sensitivity of detection. It is well suited for analyzing small molecules in serum, urine, food, tissues, and industrial samples. Furthermore, since proteins are eliminated, the capillary does not need thorough washings between samples, speeding up the analysis and extending the capillary life.

Acetonitriles↗
PubMed1998

Complement activation during blood sampling procedures alters the expression of CD11b/CD18 on human neutrophils.

BACKGROUND AND OBJECTIVES: Differences in blood sampling and separation techniques can affect the quantitative levels of activation markers on different leukocyte subsets. We examined the effect of two sampling procedures of EDTA blood on the quantitative levels of two markers, the CD11b/CD18 antigen and the EG2 epitope on intracellular eosinophilic cationic protein (ECP), in neutrophils and eosinophils, respectively. MATERIALS AND METHODS: Sample I was collected directly after completion of blood donation by an open technique and constant flow from the transfer tube directly into EDTA tubes. After sampling, the transfer tube was manually closed with a clamp. Sample II was collected 45 s later by the same technique by opening the clamp. RESULTS: We found a significantly (p < 0.01) higher expression of CD11b/CD18 on neutrophils collected by sampling procedure II than on those collected by sampling procedure I. In contrast, we did not find any difference in the intracellular ECP expression between sampling procedures I and II. To further explore the mechanisms for the observed upregulation of CD11b/CD18, fragments of a transfer tube were incubated with normal human serum (NHS) and heat-inactivated NHS (NHS56), respectively, for 60 min at +37 degrees C. Leukocytes from healthy blood donors were then incubated for 15 min at +37 degrees C with these serum preparations. The CD11b/CD18 expression was significantly higher (p < 0.01) on neutrophils incubated with transfer-tube-activated NHS compared with NHS alone. However, when leukocytes were incubated with transfer tube activated NHS56, no difference was observed compared with incubation with NHS alone. In addition, by using confocal laser scanning microscopy, we could identify complement (C3c) deposits on the inner surface of the transfer tube fragments incubated in NHS, but not in NHS56, CONCLUSIONS: The quantitative level of the activation marker CD11b/CD18 on neutrophils, but not the EG2 epitope on intracellular ECP in eosinophils is significantly increased by a slight modification of the blood sampling procedure. It is suggested that the observed upregulation of CD11b/CD18 is caused by complement activation within the transfer tube. The results emphasize the importance of in-house data on the effect of variations in sampling procedures, particularly when data from healthy blood donors are included in clinical studies.

Blood Proteins↗
PubMed1998

Needle biopsies of the prostate: what constitutes adequate histologic sampling?

OBJECTIVE: The automated biopsy gun and increased screening for adenocarcinoma of the prostate have led to increased numbers of biopsies with only tiny foci of prostatic carcinoma. Consequently, the risk of failing to sample a small focus of carcinoma histologically has increased as well. Most pathologists routinely sample prostatic needle biopsies at more than 1 level. An expert panel has recently suggested that prostatic needle biopsies be sampled at at least 2 levels. However, there have been no studies measuring the amount of additional tissue sampled by multiple levels versus 1 level. METHODS: Forty-two prostatic needle biopsies were serially sectioned at 4-microm levels. Hematoxylin-eosin-stained slides were prepared from every fifth section. The total length of each biopsy was compared with the length sampled by 1 level (50% through the block) and 3 levels (25%, 50%, and 75% through the block). RESULTS: Sampling the tissue at 1 level missed an average of 23.4% of the total biopsy length. Sampling the tissue at 3 levels significantly improved this average to 7% (P = .0001). CONCLUSIONS: This study shows that a single histologic section of a prostatic needle biopsy often fails to sample a significant portion of available tissue. This could occasionally result in failure to sample a small focus of prostatic carcinoma. The authors recommend that prostatic needle biopsies be routinely sampled at 3 levels (approximately 25%, 50%, and 75% through the block).

Adenocarcinoma↗
PubMed2003

A model to estimate the optimal sample size for microbiological surveys.

Estimating optimal sample size for microbiological surveys is a challenge for laboratory managers. When insufficient sampling is conducted, biased inferences are likely; however, when excessive sampling is conducted valuable laboratory resources are wasted. This report presents a statistical model for the estimation of the sample size appropriate for the accurate identification of the bacterial subtypes of interest in a specimen. This applied model for microbiology laboratory use is based on a Bayesian mode of inference, which combines two inputs: (ii) a prespecified estimate, or prior distribution statement, based on available scientific knowledge and (ii) observed data. The specific inputs for the model are a prior distribution statement of the number of strains per specimen provided by an informed microbiologist and data from a microbiological survey indicating the number of strains per specimen. The model output is an updated probability distribution of strains per specimen, which can be used to estimate the probability of observing all strains present according to the number of colonies that are sampled. In this report two scenarios that illustrate the use of the model to estimate bacterial colony sample size requirements are presented. In the first scenario, bacterial colony sample size is estimated to correctly identify Campylobacter amplified restriction fragment length polymorphism types on broiler carcasses. The second scenario estimates bacterial colony sample size to correctly identify Salmonella enterica serotype Enteritidis phage types in fecal drag swabs from egg-laying poultry flocks. An advantage of the model is that as updated inputs from ongoing surveys are incorporated into the model, increasingly precise sample size estimates are likely to be made.

Animals↗
PubMed2001

Improved rapid sampling for in vivo kinetics of intracellular metabolites in Saccharomyces cerevisiae.

An integrated approach is used to develop a rapid sampling strategy for the quantitative analysis of in vivo kinetic behavior based on measured concentrations of intracellular metabolites in Saccharomyces cerevisiae. Emphasis is laid on small sample sizes during sampling and analysis. Subsecond residence times are accomplished by minimizing the dead volume of the sterile sampling system and by maximizing flow rates through application of vacuum to the sampling tubes in addition to the overpressure in the fermenter. A specially designed sample tube adapter facilitates sampling intervals of 4 to 5 s for various test tube types. Statistical analysis of the results obtained from enzymatic and liquid chromatography mass spectrometry (LC-MSMS) analysis of the metabolite concentrations was used to optimize the sampling protocol. The most notable improvement is reached through the introduction of vacuum drying of the cell extract. The presented system is capable of reliably dealing with fermenter samples as small as 1-g with a variation of less than 3%, and is thus ideally suited for intracellular measurements on small, lab-scale fermenters.

Biomass↗
PubMed2001

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.

Bias↗
PubMed2003

Blinded sample size reassessment in non-inferiority and equivalence trials.

Even in situations where the design and conduct of clinical trials is highly standardized, there may be a considerable between-study variation in the observed variability of the primary outcome variable. As a consequence, performing a study in a fixed sample size design implies a considerable risk of resulting in a too high or too low sample size. This difficulty can be alleviated by applying a design with internal pilot study. After a provisional sample size calculation in the planning stage, a portion of the planned sample is recruited and the sample size is recalculated on the basis of the observed variability. To comply with the requirement of some regulatory guidelines only blinded data should be used for the reassessment procedure. Furthermore, the effect on the type I error rate should be quantified. The current literature presents analytical results on the actual level in the t-test situation only for superiority trials. In these situations, blinded sample size recalculation does not lead to an inflation of the type I error rate. We extended the methodology to non-inferiority and equivalence trials with normally distributed outcome variable and hypotheses formulated in terms of the ratio and difference of means. Surprisingly, in contrast to the case of testing superiority, we observed actual type I error rates above the nominal level. The extent of inflation depends on the required sample size, the sample size of the internal pilot study, and the standardized equivalence or non-inferiority margin. It turned out that the elevation of the significance level is negligible for most practical situations. Nevertheless, the consequences of sample size reassessment have to be discussed case by case and regulatory concerns with respect to the actual size of the procedure cannot generally be refuted by referring to the fact that only blinded data were used.

Asthma↗
PubMedDate not supplied

A dual frame design for sampling elderly minorities and persons with disabilities.

Multiple data sources are sometimes available as potential sampling frames for population surveys, and in some situations the use of a multiple frame sample design is more advantageous than using a single sampling frame. The use of multiple sampling frames, however, has variance and bias implications, as well as sampling, data collection, and logistical considerations. These issues are addressed for a proposed dual frame sampling approach in the National Health Interview Survey (NHIS). The results of an investigation of the sampling efficiencies and operational issues in supplementing the NHIS area frame sample with a sample of elderly African and Hispanic Americans and persons with disabilities selected from Social Security Administration files are presented.

Adolescent↗
PubMed2002

SPECT imaging with off-set detector system: comparison of sampling angles 2, 4 and 6 degrees.

PURPOSE: We evaluated an off set reconstruction method for single photon emission computed tomography (SPECT), and compared it with the conventional on set reconstruction method, using sampling angles of 2, 4, and 6 degrees. METHOD: A triple-detector system was used. In the off-set acquisition, sampling angles of the opposite detector were shifted 1/2 of the sampling angles of 2, 4, and 6 degrees. For example, when projection data were acquired every 6-degrees (sampling angle = 6 degrees), the projection angles were at 0 degrees, 6 degrees, 12 degrees, and 174 degrees with one detector, and 177 degrees, 183 degrees, 189 degrees, and 357 degrees with the other, opposite, detector. The conventional on set reconstruction images were compared with an off set reconstruction for a pool phantom of uniform concentration, a hot rods phantom, a myocardial phantom, and a human study. RESULTS: The off set reconstruction method was better at all three sampling angles. FWHM (mm) were 11.02 at off-set versus 11.17 at on-set (sampling angle 2 degrees), 11.13 at off-set versus 11.48 at on-set (sampling angle 4 degrees), and 11.24 at off-set versus 11.64 at on-set (sampling angle 6 degrees), respectively. In human myocardium SPECT, visualization of the interventricular septum and cardiac cavity was improved. CONCLUSION: Off set reconstruction by means of filtered back projection will be an efficient sampling mode, having a larger number of effective projection angles.

Adult↗
PubMed2004

Distribution-abundance relationship for passerines breeding in Tunisian oases: test of the sampling hypothesis.

The positive relationship between local abundance and distribution of species is a widely recognized pattern in community ecology. However, it has been suggested that this relationship can simply be an artefact of sampling because locally rare species are less detectable then locally abundant ones, and hence their distribution can easily be underestimated. Here, we use count data to investigate the relationship between distribution and abundance of passerines breeding in a sample of oases from southern Tunisia, and we provide a test of the sampling artefact hypothesis. In particular, we checked for a difference in detection probability between localized and widespread species, and we tested if increasing the sampling effort affects the significance of the relationship. A significant positive relationship between the average local abundance of passerine species and the proportion of occupied oases was found. The use of a capture-recapture approach allowed us to estimate and to compare the detection probabilities of localized and widespread species subsets. We found that localized species were locally less detectable than widespread species, which is consistent with the main assumption of the sampling artefact hypothesis. However, increasing the detection probability of species by conducting more counts did not affect the significance of the relationship, which did not give support to the sampling artefact hypothesis. Our work implies that sampling contributed to the distribution-abundance relationship we found, but that it is unlikely that such a relationship could entirely be explained by an artefact of sampling. It also underlines the insight that can be gained by using probabilistic approaches of estimating species number and detection probability when attempting to disentangle sampling from ecological effects in community ecology studies.

Animals↗
PubMed1991

Amniocentesis or chorionic villus sampling for prenatal genetic testing: a decision analysis.

We used decision analysis to examine the strategies of amniocentesis, chorionic villus sampling, and no prenatal testing for a pregnant woman who would be 35 years of age at the expected date of delivery. Probabilities were obtained from the obstetric and genetic literature, and utilities from previously published standard reference gambles and from responses of obstetric residents and students recorded on a linear rating scale. The expected utility of amniocentesis exceeded that of chorionic villus sampling by 0.1 utility units, and of no prenatal testing by 0.12 utility units. The decision was insensitive to clinically plausible values for the probabilities of spontaneous abortion after amniocentesis and chorionic villus sampling, the probabilities of abnormal and indeterminate chorionic villus sampling results, the probability of an abnormal amniocentesis result after an indeterminate chorionic villus sampling, the sensitivities and specificities of amniocentesis and chorionic villus sampling, and the probabilities of significant maternal morbidity after first- and second-trimester therapeutic abortion. Chorionic villus sampling was preferred to amniocentesis when the utility of a first-trimester therapeutic abortion exceeded that of a second-trimester abortion by 23.2 utility units, or when the anxiety "cost" of awaiting second-trimester amniocentesis results exceeded 0.1 utility unit. We conclude that over a range of assumptions concerning the probabilities involved in the prenatal testing decision, amniocentesis was preferred to chorionic villus sampling. However, for a decision maker for whom a second-trimester therapeutic abortion would be significantly less acceptable than a first-trimester procedure, or for whom the anxiety of awaiting second-trimester chromosomal diagnosis might be an important consideration, chorionic villus sampling could become the procedure of choice.

Adult↗
PubMed2001

A study of workers' exposures to the inhalable and 'total' aerosol fractions in the primary nickel production industry using mannequins to simulate personal sampling.

This paper describes a study that was carried out at work sites in the primary nickel production industry to investigate the difference between inhalable and 'total' aerosol exposures by using the mannequin sampling method, and to compare the results with those from an earlier study where actual workers' personal exposures were assessed in the same way. Experiments were carried out at 21 work sites located in mining, milling, smelting, and refining works of two primary nickel production companies. During sampling, mannequins were used to simulate the physical presence of workers and the 'exposures' of these were obtained for strategic positions at selected work sites. The orientations of each mannequin with respect to the wind were rotated through 90 degrees every hour in order to simulate the approximate orientation-averaging corresponding to actual workers. Two samplers were placed side-by-side on each mannequin: the Institute of Occupational Medicine (IOM) inhalable aerosol sampler, and the 37-mm plastic cassette widely used as a personal sampler for 'total' aerosol. Each collected sample was analyzed to obtain both overall dust and overall nickel content. A total of 116 such sample pairs were collected. The results show that inhalable aerosol exposure levels-for both overall dust and for total nickel content-were consistently and significantly higher than the corresponding total aerosol exposure levels. Weighted least squares linear regression yielded (inhalable/'total') aerosol ratios ranging from 1.38 to 3.90 and 1.20 to 4.01, respectively, for overall dust and for total nickel content for different work sites. Comparison of these results with those from the earlier study of actual workers' personal exposures were in good agreement for most of the work sites studies. However, the actual intensities of exposure using the mannequin sampling method were consistently lower than those obtained from actual workers' personal sampling in our earlier study. The consistency of the (inhalable/'total') ratios between mannequin and actual personal sampling strongly suggests that the characteristics of the aerosol sampled by the two methods, most notably the particle size distribution, were the same. This in turn suggests that mannequin sampling can be useful in occupational hygiene for determining such properties of personal workers' exposures. It certainly provides a useful and cost effective method for determining factors at work sites in individual industry settings by which to examine the impact of changing exposure assessment from one based on 'total' aerosol to the recommended new approach based on inhalable aerosol.

Aerosols↗
PubMed2001

Uniform power method for sample size calculation in historical control studies with binary response.

Makuch and Simon gave a sample size calculation formula for historical control (HC) studies that assumed that the observed response rate in the control group is the true response rate. We dropped this assumption and computed the expected power and expected sample size to evaluate the performance of the procedure under the omniscient model. When there is uncertainty in the HC response rate but this uncertainty is not considered, Makuch and Simon's method produces a sample size that gives a considerably lower power than that specified. Even the larger sample size obtained from the randomized design formula and applied to the HC setting does not guarantee the advertised power in the HC setting. We developed a new uniform power method to search for the sample size required for the experimental group to yield an exact power without relying on the estimated HC response rate being perfectly correct. The new method produces the correct uniform predictive power for all permissible response rates. The resulting sample size is closer to the sample size needed for the randomized design than Makuch and Simon's method, especially when there is a small difference in response rates or a limited sample size in the HC group. HC design may be a viable option in clinical trials when the patient selection bias and the outcome evaluation bias can be minimized. However, the common perception of the extra sample size savings is largely unjustified without the strong assumption that the observed HC response rate is equal to the true control response rate. Generally speaking, results from HC studies need to be confirmed by studies with concurrent controls and cannot be used for making definitive decisions.

Bias↗
PubMed2006

The effect of sampling on estimates of lexical specificity and error rates.

Studies based on naturalistic data are a core tool in the field of language acquisition research and have provided thorough descriptions of children's speech. However, these descriptions are inevitably confounded by differences in the relative frequency with which children use words and language structures. The purpose of the present work was to investigate the impact of sampling constraints on estimates of the productivity of children's utterances, and on the validity of error rates. Comparisons were made between five different sized samples of wh-question data produced by one child aged 2;8. First, we assessed whether sampling constraints undermined the claim (e.g. Tomasello, 2000) that the restricted nature of early child speech reflects a lack of adultlike grammatical knowledge. We demonstrated that small samples were equally likely to under- as overestimate lexical specificity in children's speech, and that the reliability of estimates varies according to sample size. We argued that reliable analyses require a comparison with a control sample, such as that from an adult speaker. Second, we investigated the validity of estimates of error rates based on small samples. The results showed that overall error rates underestimate the incidence of error in some rarely produced parts of the system and that analyses on small samples were likely to substantially over- or underestimate error rates in infrequently produced constructions. We concluded that caution must be used when basing arguments about the scope and nature of errors in children's early multi-word productions on analyses of samples of spontaneous speech.

Birth Order↗
PubMed2004

Escherichia coli sampling reliability at a frequently closed Chicago Beach: monitoring and management implications.

Monitoring beaches for recreational water quality is becoming more common, but few sampling designs or policy approaches have evaluated the efficacy of monitoring programs. The authors intensively sampled water for E. coli (N=1770) at 63rd Street Beach, Chicago for 6 months in 2000 in order to (1) characterize spatial-temporal trends, (2) determine between and within transect variation, and (3) estimate sample size requirements and determine sampling reliability. E. coli counts were highly variable within and between sampling sites but spatially and diurnally autocorrelated. Variation in counts decreased with water depth and time of day. Required number of samples was high for 70% precision around the critical closure level (i.e., 6 within or 24 between transect replicates). Since spatial replication may be cost prohibitive, composite sampling is an alternative once sources of error have been well defined. The results suggest that beach monitoring programs may be requiring too few samples to fulfill management objectives desired. As the recreational water quality national database is developed, it is important that sampling strategies are empirically derived from a thorough understanding of the sources of variation and the reliability of collected data. Greater monitoring efficacy will yield better policy decisions, risk assessments, programmatic goals, and future usefulness of the information.

Chicago↗
PubMed2001

Outcome of first-trimester chorionic villus sampling for genetic investigation in multiple pregnancy.

OBJECTIVES: To evaluate the efficacy of and risk associated with chorionic villus sampling for genetic investigations in multiple pregnancies, and to evaluate the accuracy of the ultrasonographic detection of chorionicity during the first trimester. PATIENTS AND METHODS: A total of 198 sets of twins and nine sets of triplets from 10 087 consecutive first-trimester pregnancies undergoing chorionic villus sampling were considered. Gestational age ranged from 7 to 12.6 weeks. Assessment and confirmation of chorionicity was based on a multiplicity of features. Dichorionicity was established in 169 sets of twins (85.3%) and trichorionicity in all triplet cases, while 29 twins were considered monochorionic. Chorionic villus sampling was performed transabdominally in all but one case, and identification of the placental insertion of the umbilical cord was the main benchmark for sampling. Sampling risks were evaluated by comparing clinical outcome with that of a control population of 63 dichorionic twin pregnancies which underwent no invasive procedure. RESULTS: Determination of the presence or absence of the lambda sign led to a correct assignment of chorionicity in all cases, while the presence of a membrane thickness of 2 mm or more reflected a 100% specificity with a 22% false negative rate. Sampling was successfully performed in all cases and in only four cases (1.0%) were two needle insertions needed. At follow-up no evidence of incorrect sampling was reported. Karyotyping was provided to all patients, and in 94.1% of cases both short and long-term culture methods were carried out. No difference in fetal and perinatal losses between the study and control populations was found, but a higher rate of deliveries before 37 weeks and of low birth weight babies was noted amongst controls. CONCLUSIONS: Chorionicity in twin pregnancy can be determined with certainty between 7 and 12 weeks of gestation; in cases of confluent placentas reliability is provided by determining the presence or absence of the lambda sign. This study indicates that first-trimester transabdominal chorionic villus sampling is a highly efficient, reliable, and relatively safe approach for genetic diagnosis in twin pregnancies. Although a precise evaluation of the relative risks of chorionic villus sampling and mid-trimester amniocentesis in twins must await randomized control studies, the advantages of a first-trimester diagnosis to enable early decision-making about selective fetal reduction are obvious.

Birth Weight↗
PubMed1992

A new sampling technique that allows quantitative fit testing by using the employee's own respirator.

A new, in-mask sampling technique has been developed that enhances current quantitative respirator fit test methods. This new sampling technique eliminates the need for a permanently modified (probed) respirator for conducting fit tests. With this new technique, a sample was drawn from the breathing zone inside the respirator by means of a sampling adapter, which was temporarily attached between one of the air-purifying filters and the facepiece before a fit test was performed. To ensure that the performance of the respirator was not altered, the sampling adapter was designed so that all major functional aspects of the respirator were unchanged. This new sampling technique was evaluated on human test subjects by simultaneous sampling from a probed respirator by using two quantitative respirator fit test instruments. One instrument sampled through a conventional respirator probe; the other used the new method. Test results show that equivalent fit test data were obtained with both sampling techniques.

Equipment Design↗
PubMed2005

A Bayesian approach on sample size calculation for comparing means.

In clinical research, parameters required for sample size calculation are usually unknown. A typical approach is to use estimates from some pilot studies as the true parameters in the calculation. This approach, however, does not take into consideration sampling error. Thus, the resulting sample size could be misleading if the sampling error is substantial. As an alternative, we suggest a Bayesian approach with noninformative prior to reflect the uncertainty of the parameters induced by the sampling error. Based on the informative prior and data from pilot samples, the Bayesian estimators based on appropriate loss functions can be obtained. Then, the traditional sample size calculation procedure can be carried out using the Bayesian estimates instead of the frequentist estimates. The results indicate that the sample size obtained using the Bayesian approach differs from the traditional sample size obtained by a constant inflation factor, which is purely determined by the size of the pilot study. An example is given for illustration purposes.

Aged↗