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At least 1,711 records · Page 95Linked to original sources
PubMed2000

Factors influencing the accuracy of renal output efficiency.

Output efficiency (OE) has been proposed as an objective tool for the estimation of renal emptying. The aim of this paper was to evaluate some factors that may affect the value of this parameter obtained by a 99Tcm MAG3 renogram. In 22 patients, the effect of different types of renal background correction was calculated. In 10 patients, simultaneous gamma camera renography and multiple blood sampling allowed the error of using a heart curve instead of a plasma curve to be evaluated. Finally, an evaluation was carried out on the effect of neglecting the change of plasma activity between the end of the furosemide acquisition and the post-micturition view obtained after repositioning of the patient on the gamma camera: 142 patients who had had multiple blood sampling were retrospectively selected for that purpose. It has been shown that all these factors may significantly affect the value of OE, particularly in cases with poor renal drainage. Unless standardization of the procedure is introduced for some of these factors, the cut-off levels for good, fair and poor drainage may vary between centres.

Algorithms↗
PubMed2001

Multispectral imaging of tablets in blister packaging.

This experiment tested the hypothesis that using near-infrared (IR) imaging spectrometry on tablets through blister packs permits the identification and composition of multiple individual tablets to be determined simultaneously. Aspirin was selected for this study because its breakdown mechanism is well understood. Near-IR cameras were used to collect thousands of spectra simultaneously from a field of packaged aspirin tablets. Tablets were selected by a principal component analysis selection algorithm. Graphs of the columns of the transformation matrix showed that salicylic acid and acetylsalicylic acid in the samples were modeled by the principal components. The bootstrap error-adjusted single-sample technique chemometric-imaging algorithm was used to draw probability-density contour plots that revealed tablet composition. Choice of color was used to represent constituent identity, whereas intensity represented concentration. The percentage of usable pixels in the indium antimonide (InSb) array was 99.9%. The SEP was 0.06% of the tablet mass for both water uptake and salicylic acid production. The number of tablets that a typical near-IR camera can currently analyze simultaneously was also estimated to be approximately 1300.

Aspirin↗
PubMed1978

Sample size needed for student ratings of instruction.

The number of evaluation forms students are asked to complete is multiplying. To reduce that number, the present study determines the minimum sample size needed for accurate student ratings of instruction. Typical questionnaire items using four- and seven-category ratings scales were studied. Data for four class sizes (40, 60, 100, 140) were sampled in graduated sizes, and a standard error of the mean was computed for each sample size. A permissible error index was computed to estimate the accuracy of ratings obtained from any sample size needed for the four different class sizes. Figures are presented from which minimum sample sizes necessary for accurate student evaluation of instruction can be computed. The figures show that sampling only one-third of classes of 100-140 students is sufficient to obtain accurate evaluations.

Evaluation Studies as Topic↗
PubMed1991

[Statistics for dentists. Confidence intervals].

The mean score of a sample deviates most probably from the mean score of the population, in which one is most interested. It is possible to calculate a kind of minimum and maximum value, the so called confidence interval, which indicates the position of the mean score of the population. Some worked examples elucidate the procedure of constructing such confidence intervals for the population mean, using the standard error of the (sample) mean (SEM).

Confidence Intervals↗
PubMed2002

Exact group-sequential designs for clinical trials with randomized play-the-winner allocation.

The use of both sequential designs and adaptive treatment allocation are effective in reducing the number of patients receiving an inferior treatment in a clinical trial. In large samples, when the asymptotic normality of test statistics can be utilized, a standard sequential design can be combined with adaptive allocation. In small samples the planned error rate constraints may not be satisfied if normality is assumed. We address this problem by constructing sequential stopping rules with specified properties by consideration of the exact distribution of test statistics under a particular adaptive allocation scheme, the randomized play-the-winner rule. Using this approach, compared to traditional equal allocation trials, trials with adaptive allocation are shown to require a larger total sample size to achieve a given power. More interestingly, the expected number patients allocated to the inferior treatment may also be larger for the adaptive allocation designs depending on the true success rates.

Binomial Distribution↗
PubMed1982

Errors in measurement and reporting of serum markers in patients with germ cell tumors.

Elevation of the serum value of either human chorionic gonadotropin or alpha-fetoprotein in patients with germ cell testicular tumors is often accepted as evidence for persistent malignancy in the absence of histologic confirmation. These laboratory values are not subject to review and confirmation, unlike histologic diagnosis. We report 3 cases in which serum marker values were incorrectly reported to be elevated by commercial laboratories over a thirteen-month period and suggest a method for handling serum samples to avoid errors in diagnosis.

Adult↗
PubMed1997

Sampling and analytical quality control of the determination of aluminium in soybean leaves.

A pot trial was set up with nine soil types, each replicated five times, in randomized blocks, to investigate the effect of soil properties on the uptake of Al by soybean plants. The variance of the measurements was estimated using five replicates of each soil type. This then enabled the statistical significance of the difference between results for each soil type to be established. The analytical variance was determined by two analyses per pot. Systematic errors during the analytical procedure were estimated by the analysis of reagent blanks and CRMs. Analysis of variance (ANOVA) was used to estimate the proportions of total variance contributed by analysis, sampling and geochemistry. Robust statistics were required because of the high sensitivity of classical ANOVA to a small number of outlying values, due to either technical or geochemical causes. In the case study described here, traditional analytical quality control apparently gave a satisfactory result. However, the results from robust ANOVA showed that the sampling error was the limiting factor for this application. It is suggested that the environmental analyst must consider errors from procedures of both sampling and analysis of environmental samples.

Aluminum↗
PubMed1984

Collection and handling of 24-hour urine specimens for measurement of analytes related to renal calculi.

Analysis for calcium, magnesium, phosphorus, oxalate, uric acid, and creatinine in 24-h urine collections is often needed for the differential diagnosis of patients with renal calculi. Considerable attention has been given to improving the methods of analysis, but improper sample collection and processing can cause significant errors for calcium and oxalate in urine samples not treated with acid and for uric acid in urine samples not treated with base. The errors are related to the concentration of the analyte, the interval the sample is stored before analysis, and the original pH of the urine sample. We describe here a system of sequential acidification (to pH 1.5) and alkalinization (to pH 9) of 24-h urine samples, followed by heating at 56 degrees C for 10 min. This procedure allows accurate analysis for all the above analytes in the same 24-h collection of urine. We validated the sample-treatment protocol for 80 24-h urine collections.

Calcium↗
PubMed2005

No association between the putative functional ZDHHC8 single nucleotide polymorphism rs175174 and schizophrenia in large European samples.

BACKGROUND: It has been recently reported that a functional variant in the ZDHHC8 gene encoding a putative palmitoyltransferase directly confers susceptibility to schizophrenia in females (). METHODS: We investigated the putative risk allele (rs175174) in four schizophrenia association samples including a Bulgarian proband and parent sample (474 trios) and three case-control panels of European origin (1028 patients/1253 control subjects) in an attempt to replicate these findings. RESULTS: Our results do not support the hypothesis that genetic variation at rs175174 is associated with increased risk for schizophrenia nor do they suggest the presence of gender-specific differences. CONCLUSIONS: Our data suggest that the reported genetic association by either represents type I error resulting from sampling variance or that rs175174 is in linkage disequilibrium (LD) with the functional variant for schizophrenia and different LD patterns obscure the detection of association.

Acyltransferases↗
PubMed2006

High-precision measurement of mercury isotope ratios in sediments using cold-vapor generation multi-collector inductively coupled plasma mass spectrometry.

An on-line Hg reduction technique using stannous chloride as the reductant was applied for accurate and precise mercury isotope ratio determinations by multi-collector (MC)-ICP/MS. Special attention has been paid to ensure optimal conditions (such as acquisition time and mercury concentration) allowing precision measurements good enough to be able to significantly detect the anticipated small differences in Hg isotope ratios in nature. Typically, internal precision was better than 0.002% (1 RSE) on all Hg ratios investigated as long as approximately 20 ng of Hg was measured with a 10-min acquisition time. Introducing higher amounts of mercury (50 ng Hg) improved the internal precision to <0.001%. Instrumental mass bias was corrected using (205)Tl/(203)Tl correction coupled to a standard-sample bracketing approach. The large number of data acquired allowed us to validate the consistency of our measurements over a one-year period. On average, the short-term uncertainty determined by repeated runs of NIST SRM 1641d Hg standard during a single day was <0.006% (1 RSD) for all isotope pairs investigated ((202)Hg/(198)Hg, (202)Hg/(199)Hg, (202)Hg/(200)Hg, and (202)Hg/(201)Hg). The precision fell to <0.01% if the long-term reproducibility, taken over 11 months (over 100 measurements), was considered. The extent of fractionation has been investigated in a series of sediments subject to various Hg sources from different locations worldwide. The ratio (202)Hg/(198)Hg expressed as delta values (per mil deviations relative to NIST SRM 1641d Hg standard solution) displayed differences from +0.74 to -4.00 per thousand. The magnitude of the Hg fractionation per amu was constant within one type of sample and did not exceed 1.00 per thousand. Considering all results (the reproducibility of Hg standard solutions, reference sediment samples, and the examination of natural samples), the analytical error of our delta values for the overall method was within +/-0.28 per thousand (1 SD), which was an order of magnitude lower than the extent of fractionation (4.74 per thousand) observed in sediments. This study confirmed that analytical techniques have reached a level of long-term precision and accuracy that is sufficiently sensitive to detect even small differences in Hg isotope ratios that occur within one type of samples (e.g., between different sediments) and so far have unequivocally shown that Hg isotope ratios in sediments vary within approximately 5 per thousand.

Chemistry Techniques, Analytical↗
PubMed2006

Sampling context affects MLU in the language of adolescents with Down syndrome.

PURPOSE: The authors describe the procedures used to explain an unexpected finding that adolescents with Down syndrome (DS) had a lower mean length of utterance (MLU) than typically developing (TD) children in interviews without picture support, but not in narratives supported by wordless picture books. They hypothesize that the picture support of the narrative context increased the MLU for the group with DS alone. METHOD: Adolescents with DS (n = 14) and TD children (n = 14) matched for receptive syntax narrated picture storybooks and participated in interviews. Transcription reliability, intelligibility/fluency, grammatical errors, discourse and sampling contexts, and discourse characteristics were examined for their effects on MLU. RESULTS: The DS group showed a greater responsiveness to adult questions than the TD group; an alternate MLU without yes/no responses showed the same interaction of group and context as the original finding. An additional comparison of MLUs, obtained from narratives present in the interview and narratives elicited using picture books, showed that picture support in narrative increased MLUs only for the group with DS. CONCLUSION: Picture support, rather than narrative context alone, increased MLUs for the group with DS. Clinical use of narratives and picture support in assessment and intervention with individuals with DS is discussed.

Adolescent↗
PubMed1991

Magnetic resonance imaging (MRI) and model-free estimates of brain volume determined using the Cavalieri principle.

A complete set of parallel (coronal) slices through a fixed human forebrain was generated by magnetic resonance imaging (MRI) and the Cavalieri principle, combined with point counting, was used to estimate brain volume. Alternative sampling schemes for estimating volume were then assessed by taking systematic and simple random selections of slices. Later, the brain was weighed and its fixed volume determined by fluid displacement. For the complete set of n = 28 MRI slices, the volume (1025 ml) was estimated with a coefficient of error (CE) of less than 1%. Decreasing the number of slices by systematic sampling increased the CE but this was still only 5% when just 5-6 slices were analysed. Estimated volumes varied from 947 ml to 1098 ml. Simple random sampling was less efficient (estimated volumes for 5-6 slices were 644-1187 ml). The forebrain actually weighed 1090 g and displaced 1060 ml of fluid. A set of 14 other brains was physically sliced in order to assess sampling errors in the context of observed brain-to-brain variation. It was found that 5-6 slices per brain is enough to yield efficient estimates of mean brain volume. The findings demonstrate the practicability of using MRI to estimate brain volumes unbiasedly and efficiently. The methods have great potential for noninvasive, longitudinal studies on in vivo brains and other organs.

Brain↗
PubMed1997

Foot position awareness in younger and older men: the influence of footwear sole properties.

OBJECTIVES: To test the hypotheses that foot position awareness is related positively to stability, positively to shoe sole hardness, and negatively to shoe sole thickness, and that foot position awareness declines with advancing years. SETTING: Older subjects were consecutive volunteers from a medical clinic; younger subjects were volunteers from the community. DESIGN: Randomized-order, cross-over, controlled comparison. PARTICIPANTS: Older subjects were a random sample of 13 healthy men, mean age 72.58 years, SD +/- 4.50. Younger subjects were a random sample of 13 male subjects from the general population, mean age 28.13 years, SD +/- 3.96. Additional selection criteria were absence of disabilities influencing ability to walk and no history of frequent falls. MEASUREMENTS: Balance failure frequency, defined as falls per 100 meters of beam walking; rearfoot angle in degrees, measured via an optical position measurement system; perceived maximum supination when walking, in degrees, estimated by subjects using a ratio scale; foot position error, in degrees, was defined as the rearfoot angle minus perceived maximum supination. RESULTS: Foot position error during walking: (1) increases with advancing years; footwear conditions absolute mean error for older sample of 15.48 degrees, SE +/- 1.56 degrees, and younger sample 5.44 degrees, SE +/- 1.03 degrees (P > .001); (2) is positively related to stability (r = .367, P < .001); (3) is positively related to midsole thickness (F(1,11) = 19.89, P < .001); (4) is negatively related to midsole hardness (F(2,22) = 29.80, P < .001); (5) correlates best with perceived maximum supination (r = .901, P < .001). CONCLUSION: Foot position awareness is related causally to stability; shoes with thin, hard soles provide better stability for men than those with thick, soft midsoles. Foot position awareness declines with advancing years.

Adult↗
PubMed2005

Improvements for comparative analysis of changes in diversity of microbial communities using internal standards in PCR-DGGE.

The use of internal standards both during DNA extraction and PCR-DGGE procedure gives the opportunity to analyse the relative abundance of individual species back to the original sample, thereby facilitating relative comparative analysis of diversity. Internal standards were used throughout the DNA extraction and PCR-DGGE to compensate for experimental variability. Such variability causes decreased reproducibility among replicate samples as well as compromise comparisons between samples, since experimental errors cannot be differentiated from actual changes in the community abundance and structure. The use of internal standards during DNA extraction and PCR-DGGE is suitable for ecological and ecotoxicological experiments with microbial communities, where relative changes in the community abundance and structure are studied. We have developed a protocol Internal Standards in Molecular Analysis of Diversity (ISMAD) that is simple to use, inexpensive, rapid to perform and it does not require additional samples to be processed. The internal standard for DNA extraction (ExtrIS) is a fluorescent 510-basepair PCR product which is added to the samples prior to DNA extraction, recovered together with the extracted DNA from the samples and analysed with fluorescence spectrophotometry. The use of ExtrIS during isolation of sample DNA significantly reduced variation among replicate samples. The PCR internal standard (PCR(IS)) originates from the Drosophila melanogaster genome and is a 140-basepair long PCR product, which is amplified by non-competitive primers in the same PCR reaction tubes as the target DNA and analysed together with the target PCR product on the same DGGE gel. The use of PCR(IS) during PCR significantly reduced variation among replicate samples both when assessing total PCR product and when comparing bands representing species on a DGGE gel. The entire ISMAD protocol was shown to accurately describe changes in relative abundance in an environmental sample using PCR-DGGE. It should, however, be mentioned that despite the use of ISMAD some inherent biases still exist in DNA extraction and PCR-DGGE and these should be taken into consideration when interpreting the diversity in a sample based on a DGGE gel.

Bacteria↗
PubMed1989

Sodium oxalate corrects calcium interference in Lowry protein assay.

We have previously noted that high levels (10 mM) of calcium interfere with protein determination in the Lowry assay. While there are numerous reports in the literature of substances interfering with the Lowry assay, none of these interfering substances are as ubiquitous as calcium. We hypothesized that physiologic levels of calcium may interfere with the protein determination as measured by the Lowry assay. To test this hypothesis, bovine serum albumin standards from 12.5 to 1600 micrograms/ml were tested in the Lowry assay in the presence of calcium chloride concentrations from 0 to 5 mM. In low protein concentrations (12.5-50 micrograms/ml) 1 to 2 mM calcium induced errors of up to 384%. In samples containing 100 to 400 micrograms/ml protein, 1 to 2 mM calcium induced errors of up to 40%. The addition of sodium oxalate to calcium-spiked protein samples significantly reduced the errors in protein determination at all calcium concentrations tested. This effect also is seen throughout the range of protein concentrations tested (50-1600 micrograms/ml). In most cases sodium oxalate pretreatment of samples used in the Lowry assay reduces errors by 70-95%. Physiologic levels of calcium induce significant errors in the estimation of protein concentration using the Lowry method. Routine pretreatment of Lowry samples with sodium oxalate will provide a more accurate estimation of the protein concentration in biological systems.

Animals↗
PubMed1986

Modified lumiflavin procedure for determination of riboflavin in soybean.

Investigation of the application of different methods for riboflavin determination proved the lumiflavin method recommended by Hausheer et al. to be the most suitable one for determining riboflavin in materials of complex composition, such as soybean. However, due to inadequate preparation of the blank sample, the method is burdened by a positive error. By modifying the blank sample and certain modifications in the procedure, more precise results, greater speed and simplification of the method were achieved. The soybean sample analysed by this modified procedure gave a mean recovery and standard error of 102.9 +/- 2.1 for added riboflavin, which is very satisfactory.

Flavins↗
PubMed2006

Low salivary cortisol and elevated depressive affect among rural men in Botswana: reliability and validity of laboratory results.

Most research on hypothalamic-pituitary-adrenal axis function under aversive conditions has focused on relatively increased acute episodic, or chronic secretions as an operationalization of "stress." Severe or recurrent stress, perhaps in interaction with individual characteristics, results in chronically decreased HPA function among some persons suffering from posttraumatic stress disorder. Little evidence exists to assess the population distribution of chronic low cortisol in different free-ranging human populations, as a manifestation of past trauma or stress. This study reports findings of chronically depressed ambulatory salivary cortisol among rural-dwelling Batswana men (n=30) compared with men living in Gaborone (n=34), the capital of Botswana, based on repeated ambulatory sampling. Out of 914 saliva samples analyzed by radioimmunoassay, 268 (29.3%) samples (41 urban, 227 rural) were below the minimum detectable dose (<MDD of 0.034 ug/dL) of the assay. Low values were distributed across comparable times of day as were =MDD samples. There was significant clustering of low cortisol within individuals; percentage of intra-individual repeats that were <MDD ranged from zero to 94.1% for rural participants (median=59.8%; mean=54.8%; SD=27.8%), and from zero to 40% for urban (median=0%; mean=8%; SD=11.9%). There was no association between number of repeats and proportion <MDD (P[F=-0.47]=0.639; beta(1)=-0.0045+/-0.0019). Examination of laboratory quality control suggests that this pattern is not a result of measurement error, or poor sample preservation, but instead reflects a difference from residing in a remote rural versus a central urban community.

Adolescent↗
PubMed1994

Scatter compensation in digital chest radiography using the posterior beam stop technique.

A new scatter compensation technique for computed radiography based on posterior beam stop (PBS) sampled scatter measurements and the bicubic spline interpolation technique was proposed. Using only a single exposure, both the clinical image and an array of scatter measurements, which were interpolated into a smooth scatter-only image, were simultaneously acquired. The scatter was subtracted from the clinical image to generate the primary-only image. To gauge the accuracy of scatter estimation, both quantitative and interpolation errors were evaluated. The PBS measurements were compared against the standard beam stop method at 16 locations in an anatomical phantom, resulting in quantitative errors of 2.7% relative to the scatter or 6.8% relative to the primary. Also measured were the interpolation error over 64 interpolation sample locations and 64 midpoint sample locations in the anatomical phantom. The combined interpolation error was 1.9% relative to the scatter or 8.0% relative to the primary. At the interpolation sample locations, the errors were identical between the phantom radiograph and digital portable chest radiographs from five patients. By summing the quantitative and interpolation errors in quadrature, the overall error of the PBS SISTER (scatter interpolation-subtraction technique for radiography) method was 3.3% relative to the scatter or 10% relative to the primary, which was adequate for dual-energy imaging purposes (less than 10% error relative to the scatter or 20% relative to the primary). The change of image contrast, noise, and signal-to-noise ratio (SNR) at six locations in the anatomical phantom were quantitatively analyzed. Contrast and noise were equally enhanced in all anatomical regions, resulting in approximately the same SNR before and after compensation.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗