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At least 289 records · Page 16Linked to original sources

Risk among men who have sex with men in the United States: a comparison of an Internet sample and a conventional outreach sample.

This study compared the demographics and risk behaviors of two samples of men who have sex with men (MSM), using cross-sectional data that were collected via the Internet and through conventional bar-based outreach. The Internet sample was significantly older, more likely to identify as "bisexual," and less educated than the bar sample. After controlling for age and education, few differences were observed between the samples. However, three variables that markedly differentiated the samples were history of sexually transmitted disease infection, HIV serostatus, and sources utilized to obtain health information. No difference in Internet use was found. Based on the possible decreased social desirability promoted by the use of electronic data collection methodologies, these findings provide preliminary evidence that Internet and bar respondents are similar and that the Internet may serve as an expedient as well as reliable methodology to increase understanding of risk among MSM.

Adult↗

Reaction times of younger and older men: effects of compound samples and a prechoice signal on delayed matching-to-sample performances.

Five younger (18 to 23 yrs) and five older (65 to 73 yrs) men were exposed to a series of immediate and delayed (0 to 15 seconds) matching-to-sample problems. Presentation of the pairs of delayed comparison stimuli was either signaled or unsignaled, and the sample contained either 1, 2, or 3 elements, one of which appeared as the positive stimulus. During initial sessions, unlimited time was available to respond. Subsequently, correct responses were reinforced only if they occurred within a specified time limit. A general finding was slower responding with increased delay and with increased number of sample elements. These effects were reduced when the comparison stimuli were signaled and when time limits were in effect. Errors increased as a function of the manipulations of sample complexity and time limits, but did not change systematically when the delay between sample and comparison stimuli was varied. Although the younger men generally responded more quickly than the older ones, men of both ages showed increased speeds when limits were placed on response time, and these changes were maintained when the temporal contingencies were removed.

Adolescent↗

Sample-stimulus discriminability and sensitivity to reinforcement in delayed matching to sample.

Five pigeons were trained in a delayed matching-to-sample task with red and green stimuli. The retention interval between sample-stimulus presentation and the availability of the choice stimuli was varied between 0.01 s and 12 s within each session. The probability of food produced by correct-red and correct-green responses was varied across conditions. Sample-stimulus discriminability and response bias were measured at four different retention intervals. The results of these analyses showed an interaction between the discriminability of the sample stimuli and the control exerted by differential reinforcement. At longer retention intervals, sample discriminability decreased and sensitivity of choice behavior to changes in the red/green reinforcer ratio increased. An analogous relation has been reported in conditional discriminations in which the physical disparity of stimuli has been varied. This correspondence suggests that increasing the delay between presentation of one of two stimuli and an opportunity to respond discriminatively to it may be functionally similar to increasing the physical similarity of the two stimuli.

Journal Article↗

Charcoal sampling and gas chromatographic determination of N,N-dimethylformamide in air samples from a polyurethane plant.

A charcoal sampling method and a gas chromatographic determination of N,N-dimethylformamide in the air of a plant producing polyurethane lumps is described. The collection efficiency was checked by drawing standard N,N-dimethylformamide air mixtures through the sampling tube at 0.1 1/min and detecting the organic vapors spectrophotometrically at 215.4 nm. At 1,000 mg/m3, samplings could be carried out for 190 min with negligible N,N-dimethylformamide losses (lower than 1%). The analysis of N,N-dimethylformamide was performed by gas chromatography on Porapack Q and Tenax GC after extraction with 2 ml of acetone/100 mg of charcoal, with a mean recovery of 90 (SD 2) %, in the range of 0.05-0.5 mg of N,N-dimethylformamide/100 mg of charcoal. The relative standard deviation of the entire procedure was 3.5%. Because of the good adsorbing efficiency of the charcoal, short-term sampling could be carried out at a relatively high N,N-dimethylformamide concentration. Stationary and personal sampling resulted in mean values ranging between 1.26 and 1.60 mg/m3. The method is particularly suitable in instances where other pollutants are present, and therefore it can be used also for other work areas as well.

Adsorption↗

[A simple method for regional cerebral blood flow measurement by one-point arterial blood sampling and 123I-IMP microsphere model (Part 2): A study of time correction of one-point blood sample count].

In our previous paper regarding determination of the regional cerebral blood flow (rCBF) using the 123I-IMP microsphere model, we reported that the accuracy of determination of the integrated value of the input function from one-point arterial blood sampling can be increased by performing correction using the 5 min: 29 min ratio for the whole-brain count. However, failure to carry out the arterial blood collection at exactly 5 minutes after 123I-IMP injection causes errors with this method, and there is thus a time limitation. We have now revised our method so that the one-point arterial blood sampling can be performed at any time during the interval between 5 minutes and 20 minutes after 123I-IMP injection, with addition of a correction step for the sampling time. This revised method permits more accurate estimation of the integral of the input functions. This method was then applied to 174 experimental subjects: one-point blood samples collected at random times between 5 and 20 minutes, and the estimated values for the continuous arterial octanol extraction count (COC) were determined. The mean error rate between the COC and the actual measured continuous arterial octanol extraction count (OC) was 3.6%, and the standard deviation was 12.7%. Accordingly, in 70% of the cases, the rCBF was able to be estimated within an error rate of 13%, while estimation was possible in 95% of the cases within an error rate of 25%. This improved method is a simple technique for determination of the rCBF by 123I-IMP microsphere model and one-point arterial blood sampling which no longer shows a time limitation and does not require any octanol extraction step.

Adult↗

Bias and Sampling Error of the Estimated Proportion of Genotypic Variance Explained by Quantitative Trait Loci Determined From Experimental Data in Maize Using Cross Validation and Validation With Independent Samples.

Cross validation (CV) was used to analyze the effects of different environments and different genotypic samples on estimates of the proportion of genotypic variance explained by QTL (p). Testcrosses of 344 F(3) maize lines grown in four environments were evaluated for a number of agronomic traits. In each of 200 replicated CV runs, this data set was subdivided into an estimation set (ES) and various test sets (TS). ES were used to map QTL and estimate p for each run (p(ES)) and its median (p(ES)) across all runs. The bias of these estimates was assessed by comparison with the median (p(TS.ES)) obtained from TS. We also used two independent validation samples derived from the same cross for further comparison. The median p(ES) showed a large upward bias compared to p(TS.ES). Environmental sampling generally had a smaller effect on the bias of p(ES) than genotypic sampling or both factors simultaneously. In independent validation, p(TS.ES) was on average only 50% of p(ES). A wide range among p(ES) reflected a large sampling error of these estimates. QTL frequency distributions and comparison of estimated QTL effects indicated a low precision of QTL localization and an upward bias in the absolute values of estimated QTL effects from ES. CV with data from three QTL studies reported in the literature yielded similar results as those obtained with maize testcrosses. We therefore recommend CV for obtaining asymptotically unbiased estimates of p and consequently a realistic assessment of the prospects of MAS.

Journal Article↗

A confirmatory factor analysis of the WAIS-III in a clinical sample with crossvalidation in the standardization sample.

A maximum likelihood confirmatory factor analysis of the Wechsler Adult Intelligence Scale-III (WAIS-III) was performed by applying LISREL 8 to a clinical sample (n=328). Analyses were designed to determine which of the nine hypothesized oblique factor solutions could best explain intelligence as measured by the WAIS-III in the general clinical sample. Competing latent variable models were identified in previous studies and a priori model modifications were made to test derivations of the nine base models. Results in the clinical sample were crossvalidated by testing all models in the normative sample used in the standardization of the scale. Findings in both the clinical and standardization samples supported a six-factor model including Semantic Memory, Verbal Reasoning, Constructional Praxis, Visual Reasoning, Working Memory, and Processing Speed factors. Our analysis differed from that presented in the WAIS-III manual as we tested more complex models of intelligence in addition to the ones evaluated by the test publishers. As a result, a six-factor model that corresponded to an expanded version of a model based on Horn's Gf-Gc theory was empirically supported as having the best fit to the data. More complex derivations of this model failed to achieve sufficient goodness of fit.

Journal Article↗

Comparison of insulin sensitivity indices calculated from standard 3-sampled and frequently sampled oral glucose tolerance test.

OBJECTIVE: Three-sampled oral glucose tolerance test is the most frequently used method for evaluation of impairment of glucose homeostasis in daily clinical practice. The aim of this study was to answer the question if insulin sensitivity indices (ISI) calculated from standard 3-sampled oral glucose tolerance test (3SoGTT) provide adequate information compared to the outcome when calculated from frequently sampled oral glucose tolerance test (FSoGTT). METHODS: A total of 73 subjects (aged 17-59 years, BMI 17.9-41.8 kg/m2) underwent a standard frequently sampled oral glucose tolerance test (FSoGTT). Selected indices of insulin sensitivity were calculated using plasma glucose and insulin concentrations from FSoGTT and from samples obtained in 0, 60 and 120 min of the oGTT (3SoGTT). Areas under the peripheral concentration curves of insulin and glucose (AUCi, AUCg) from both approaches were compared. RESULTS: Insulin sensitivity calculated from 3SoGTT was significantly higher compared to the sensitivity calculated from FSoGTT expressed as insulin sensitivity indices ISI Cederholm (ISI(Ced)) and ISI Matsuda (ISI(Mat)), p<0.001 and p<0.05, respectively. There was a difference in AUCg between values estimated from 3SoGTT and FSoGTT (p<0.05). These differences nearly disappeared when the BMI groups (normal weight and overweight/obese) were evaluated separately. No differences were found in AUCi and the AUCg:AUCi ratio between two approaches. CONCLUSIONS: It might be supposed that on using 3SoGTT the ISI(Mat) provides greater objectivity in assessing insulin sensitivity than ISI(Ced). Although insulin sensitivity is overestimated when calculated from 3SoGTT, the approach is still valuable for identifying subjects with insulin resistance.

Adolescent↗

[Agreement in the determination of electrolytes in samples of serum and plasma. Stability of these samples kept for 2 hours at room temperature with uncovered tubes].

UNLABELLED: The determination of electrolytes in the clinical laboratories is carried out in samples of serum or plasma in situations that tubes remain open during a lingering time. OBJECTIVE: To estimate the agreement and the interchangeability in the determination of electrolytes for three types of tubes (serum with separator, plasma with and without separator) in samples that remain at room temperature and open up to two hours. MATERIAL AND METHODS: Samples of 36 voluntary patients were selected determining the levels of sodium, potassium, chlorine, calcium, magnesium and phosphate in the three tubes on time 0 (basal), 60 and 120 minutes. The agreement was estimated by means of the intraclass correlation coefficient (ICC) and the interchangeability of results by means of lineal regression. RESULTS: Agreement among the samples was very high with ICC higher than 0.9 in all basal determinations except for the potassium for which the presence of a constant systematic error was detected between serum and two tubes of plasma. The stability of the parameters is good in all the samples. CONCLUSIONS: It is possible the use of different types of tubes in the determination of electrolytes under the working conditions of the clinical laboratories. The determination of potassium needs to be corrected before the exchange of results obtained with serum and plasma. The stability in the two first hours is good in all the cases.

Blood Chemical Analysis↗

Sampling and preparation of sample for chemical examination.

Sampling and methods for reducing a laboratory sample to a test sample are discussed, with particular emphasis on sampling peanuts for aflatoxin analysis as a practical example. The only way to control the total error in the analysis of this heterogeneous product is to take and to analyze many and large samples.

Aflatoxins↗

Estimating sample sizes for a two-stage sampling survey of seroprevalence of pseudorabies virus (PRV)-infected swine at a regional level in The Netherlands.

In the European Union, vaccination campaigns against Pseudorabies virus (PRV) in swine have been started to eradicate PRV. Specific sampling designs are needed to monitor PRV seroprevalence at a regional level. This paper demonstrates how sampling theory can be applied to design a disease seroprevalence survey, using PRV as an example. In the spring of 1994, the four regions in the Netherlands covered by the regional Animal Health Services were monitored with respect to PRV seroprevalence. Per region, blood samples from approximately 1400 herds, with two animals per herd, were collected. The sampling design accounted for stratification by fattening pig and sow population within each region. The regional PRV seroprevalence of swine in the Southern region was the highest (24.9%), closely followed by the PRV seroprevalence of swine in the Eastern region (20.5%). These regions have the highest density of swine in the Netherlands. The PRV seroprevalence in the Western and Central region (11.7%) was about half of the seroprevalence in the Southern and Eastern regions; the lowest regional PRV seroprevalence was observed in the Northern region (3.5%). The Northern part also has the lowest pig density. The PRV seroprevalence was approximately two times higher in sows than in fattening pigs.

Animals↗

Optimization of household survey sampling without sample frames.

There are a few sampling methods available to survey households in situations where sample frames are either unavailable or are unreliable. The most popular of these methods is the expanded programme of immunization (EPI) sampling method, which has been used in low-income countries. The purpose of this paper is to explain how mathematical programming can be used to optimize EPI and other household survey sampling methods in these situations.

Developing Countries↗

Evaluation of immunization coverage by lot quality assurance sampling compared with 30-cluster sampling in a primary health centre in India.

The immunization coverage of infants, children and women residing in a primary health centre (PHC) area in Rajasthan was evaluated both by lot quality assurance sampling (LQAS) and by the 30-cluster sampling method recommended by WHO's Expanded Programme on Immunization (EPI). The LQAS survey was used to classify 27 mutually exclusive subunits of the population, defined as residents in health subcentre areas, on the basis of acceptable or unacceptable levels of immunization coverage among infants and their mothers. The LQAS results from the 27 subcentres were also combined to obtain an overall estimate of coverage for the entire population of the primary health centre, and these results were compared with the EPI cluster survey results. The LQAS survey did not identify any subcentre with a level of immunization among infants high enough to be classified as acceptable; only three subcentres were classified as having acceptable levels of tetanus toxoid (TT) coverage among women. The estimated overall coverage in the PHC population from the combined LQAS results showed that a quarter of the infants were immunized appropriately for their ages and that 46% of their mothers had been adequately immunized with TT. Although the age groups and the periods of time during which the children were immunized differed for the LQAS and EPI survey populations, the characteristics of the mothers were largely similar. About 57% (95% CI, 46-67) of them were found to be fully immunized with TT by 30-cluster sampling, compared with 46% (95% CI, 41-51) by stratified random sampling. The difference was not statistically significant. The field work to collect LQAS data took about three times longer, and cost 60% more than the EPI survey. The apparently homogeneous and low level of immunization coverage in the 27 subcentres makes this an impractical situation in which to apply LQAS, and the results obtained were therefore not particularly useful. However, if LQAS had been applied by local staff in an area with overall high coverage and population subunits with heterogeneous coverage, the method would have been less costly and should have produced useful results.

Adult↗

A comparison of rarefaction and bayesian methods for predicting the allelic richness of future samples on the basis of currently available samples.

Rarefaction methods have been introduced into population genetics (from ecology) for predicting and comparing the allelic richness of future samples (or sometimes populations) on the basis of currently available samples, possibly of different sizes. Here, we focus our attention on one such problem: Predicting which population is most likely to yield the future sample having the highest allelic richness. (This problem can arise when we want to construct a core collection from a larger germplasm collection.) We use extensive simulations to compare the performance of the Monte Carlo rarefaction (repeated random subsampling) method with a simple Bayesian approach we have developed-which is based on the Ewens sampling distribution. We found that neither this Bayesian method nor the (Monte Carlo) rarefaction method performed uniformly better than the other. We also examine briefly some of the other motivations offered for these methods and try to make sense of them from a Bayesian point of view.

Alleles↗

Options available for profiling small samples: a review of sample amplification technology when combined with microarray profiling.

The possibility of performing microarray analysis on limited material has been demonstrated in a number of publications. In this review we approach the technical aspects of mRNA amplification and several important implicit consequences, for both linear and exponential procedures. Amplification efficiencies clearly allow profiling of extremely small samples. The conservation of transcript abundance is the most important issue regarding the use of sample amplification in combination with microarray analysis, and this aspect has generally been found to be acceptable, although demonstrated to decrease in highly diluted samples. The fact that variability and discrepancies in microarray profiles increase with minute sample sizes has been clearly documented, but for many studies this does appear to have affected the biological conclusions. We suggest that this is due to the data analysis approach applied, and the consequence is the chance of presenting misleading results. We discuss the issue of amplification sensitivity limits in the light of reports on fidelity, published data from reviewed articles and data analysis approaches. These are important considerations to be reflected in the design of future studies and when evaluating biological conclusions from published microarray studies based on extremely low input RNA quantities.

Gene Expression Profiling↗

Ranked set sampling with unequal samples.

A ranked set sampling procedure with unequal samples (RSSU) is proposed and used to estimate the population mean. This estimator is then compared with the estimators based on the ranked set sampling (RSS) and median ranked set sampling (MRSS) procedures. It is shown that the relative precisions of the estimator based on RSSU are higher than those of the estimators based on RSS and MRSS. An example of estimating the mean diameter at breast height of longleaf-pine trees on the Wade Tract in Thomas County, Georgia, is presented.

Biometry↗

Analyzing Raman maps of pharmaceutical products by sample-sample two-dimensional correlation.

Sample-sample (SS) two-dimensional (2D) correlation spectroscopy is applied in this study as a spectral selection tool to produce chemical images of real-world pharmaceutical samples consisting of two, three, and four components. The most unique spectra in a Raman mapping spectral matrix are found after analysis of the covariance matrix. (This is obtained by multiplying the original mapping data matrix by itself.) These spectra are identified by analyzing the slices of the covariance matrix at the positions where covariance values are at maxima. Chemical images are subsequently produced in a univariate fashion by visually selecting the wavenumbers in the extracted spectra that are least overlapped. The performance of SS 2D correlation is compared with principal component analysis in terms of highlighting the most prominent spectral differences across the whole data set (which typically comprises several thousand spectra) and determining the total number of species present. In addition, the selection of the unique spectra by SS 2D correlation is compared with the selection obtained by the orthogonal projection approach (OPA). Both comparisons are found to be satisfactory and demonstrate that a quite simple SS 2D correlation routine can be used for producing reliable images of unknown samples. The main benefit of using SS 2D correlation is that it is based on a few data processing commands that can be executed separately and produce results that are closely related to the chemical features of the system.

Algorithms↗