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At least 433 records · Page 24Linked to original sources
PubMed1989

Multi-factor designs. II. A design for identifying instruments with sample-to-sample carryover and drift.

We describe a nearly orthogonal two-level design that involves use of a weighted analysis to estimate drift and very low amounts of sample-to-sample carryover simultaneously. Identifying systematic errors from these sources is especially important for assays of analytes presenting a large range and with a medical decision point close to zero. The design is illustrated with data for thyrotropin, where, in one run with 32 samples, 0.08% carryover was detected in the presence of concentration-dependent negative drift.

Autoanalysis↗
PubMed1988

Comparison of DNA ploidy in routine fine needle aspiration biopsy samples and paraffin-embedded tissue samples.

The nuclear DNA content was determined by flow cytometry (FCM) from unfixed fine needle aspiration (FNA) biopsy samples of 31 human tumors, and from the same tumors after their excision, fixation with formalin and embedding in paraffin. The ploidy of the histograms was the same in 29 (94%) of the 31 cases. The disagreement in two cases may be explained by clonal heterogeneity of the tumors. The DNA index of the aneuploid cases was identical in fresh and fixed samples. The coefficient of variation of the diploid peaks (P less than .001) and the mean percentage of S-phase cells (P = .06) were larger in the fixed samples. It is concluded that routine FNA biopsy is a practical and reliable method for collecting cells for FCM DNA ploidy determination.

Adenoma↗
PubMed1984

Anaerobic curved rods in genital samples of women. Performance of different selective media, comparison of detection by microscopy and culture studies, and recovery from different sampling sites.

Anaerobic curved rods (CR) frequently occur in the vaginal flora of women with non-specific vaginitis, more recently referred to as bacterial vaginosis (BV). The reasons for difficulties in culturing CR include their anaerobic nature, slow rate of growth and presence in a highly mixed flora. The present study concerns the efficiency of three culture media--blood agar, a gonococcal medium, and Columbia agar--for recovery of CR. The possibility of improving selectivity by adding various antibiotics (e.g. nalidixic acid, colistin and tinidazole) to the media was also explored. The MICs for 157 CR strains and for 80 strains of anaerobic or facultatively anaerobic bacteria isolated from vaginal samples from women with BV were therefore determined. Columbia agar containing 1 micrograms/ml tinidazole in combination with either colistin (10 micrograms/ml) or nalidixic acid (15 micrograms/ml) proved the most efficient medium for recovery of CR. These antibiotic combinations effectively suppressed growth of Gardnerella vaginalis, anaerobic cocci and species of Bacteroides.--In 291 women, comparison was made of the detection of CR morphotype bacteria in methylene-blue-stained smears and the results of vaginal cultures for CR. A long variant (2-4 micron) was found in 42% by direct microscopy and 43% by culture. A short variant (approx 1 micron), which, with two exceptions, was always concomitant with the long variant, was demonstrable in only 3% of vaginal smears and in 14% of the cultures.--Vaginal samples were approximately four times more often culture-positive for CR than were cervical samples from the same women.

Bacteria, Anaerobic↗
PubMed1983

Cell cycle homogeneity in bone marrow samples from different sites: flow cytometric evaluation of multiple samples from sheep.

The distributions of cells in each of the phases of the cell cycle, determined by flow cytometry (FCM), were compared in multiple marrow trephine biopsy samples from 3 sites (both iliac bones and sternum) in 5 sheep. Within any one animal no significant differences could be found between the proportions of cells in the G0/G1, S or G2 + M phases of the cycle from different sites. Differences between animals were detected and these were consistent for any of the sites sampled. We conclude that the proliferative characteristics of marrow cells as determined by FCM in any one animal at one time are comparable at anatomically distinct marrow sites, and that a sample from one site is representative of the whole.

Animals↗
PubMed1980

Protocols for surveys, sampling, post-collection handling, and analysis of grain samples involved in mycotoxin problems.

This report examines and summarizes current knowledge regarding mycotoxin surveys, sampling techniques, conditions conducive to post-collection production of mycotoxins in grain samples, and analytical methods for mycotoxin analysis. Priority attention is given to samples of corn suspected of containing aflatoxin. The report includes recommendations where deems appropriate by the Ad Hoc Work Group.

Aflatoxins↗
PubMedDate not supplied

Drug screening in newborns and mothers using meconium samples, paired urine samples, and interviews.

We evaluated the prevalence of illicit substance abuse by comparing drug screening results derived from meconium, urine pairs, and maternal interview. Mother/infant pairs (580) were entered into this blinded, prospective study. Prevalence of illicit substance abuse was 3.4%. The lack of prenatal care correlated with the use of cocaine (p < 0.001). Neonates born to cocaine-using mothers were more likely to be premature, to have a lower birth weight, decreased length, and smaller head circumference using unpaired t test (overall p < 0.05 using Bonferroni method for simultaneous inference). For mother/infant pairs who had positive drug screening for cocaine, the interview, maternal urine sample, and meconium sample showed equal sensitivity, although the newborn urine showed poor correlation. We suggest that the newborn urine sample could be deleted from newborn drug screening, and lack of perinatal care may serve as a marker of substance abuse.

Cocaine↗
PubMed1997

Exact equivalence test for risk ratio and its sample size determination under inverse sampling.

When data are dichotomous, this paper notes the utility of inverse sampling in establishing equivalence with respect to the risk ratio. This paper develops an exact equivalence test that accounts for the risk ratio under inverse sampling and further discusses the relationship between the exact equivalence test and the exact conditional confidence limits. Also included are an exact and two asymptotic procedures for calculation of the minimum required number of index subjects for a desired power 1--beta at a given alpha-level. Finally, this paper provides a table that summarizes the minimum required number of index subjects for powers equal to 0.90 and 0.80 in application of the proposed exact equivalence test at 0.05-level in a variety of situations.

Confidence Intervals↗
PubMed1996

Formulae and tables for the determination of sample sizes and power in clinical trials for testing differences in proportions for the two-sample design: a review.

This paper is a compendium of exact and asymptotic formulae and tables for estimating the sample size in a clinical trial with two treatment groups and a dichotomous outcome. The paper provides separate formulae for equal and unequal treatment group sizes, formulae for the calculation of power given the sample size, and complete references for all formulae and tables cited.

Binomial Distribution↗
PubMed1990

Transabdominal villus sampling in early second trimester: a safe sampling method for women of advanced age.

Transabdominal chorionic villus sampling (TA-CVS) was performed in 707 viable singleton pregnancies to exclude chromosomal abnormalities. Maternal age ranged between 36 and 49 years (mean 37.9 years); gestational age varied between 10.2 and 18.3 weeks (mean 13.3 weeks). In 639 women (90.4 per cent), a sufficient amount of chorionic tissue (greater than or equal to 10 mg) was obtained after one needle insertion; in 66 women (9.3 per cent) two insertions were needed. An abnormal chromosome pattern was established in 19 cases (2.9 per cent). Vaginal bleeding or spotting within 28 days after TA-CVS occurred in 11 cases (1.5 per cent). The completed follow-up of 678 chromosomally normal pregnancies showed an overall fetal loss rate of 2.6 per cent before 28 weeks. The overall perinatal mortality was 0.9 per cent. When relating fetal loss to gestational age at TA-CVS, this was 6.6 per cent in women sampled before 12 weeks against only 1.8 per cent after 12 weeks. At the same time, the percentage of fetal loss occurring within 2 weeks following the procedure was 75 and 30 per cent, respectively. It is suggested that these data reflect the decline in spontaneous abortion rate during this particular period of pregnancy. It is concluded that TA-CVS is an effective procedure which, when performed after the natural decrease of fetal loss, appears to be a safe option for women of advanced maternal age.

Abdomen↗
PubMed2003

Estimates, power and sample size calculations for two-sample ordinal outcomes under before-after study designs.

Sample size calculations are given for comparing two groups of subjects, typically referring to active and non-active intervention groups, on an ordinal outcome in experiments where the subjects are measured before and after intervention. These calculations apply to log-odds models with random intercepts, treatment, time and treatment-by-time interaction terms, the latter being the term of interest. The assumed forms of the odds ratios are flexible, allowing for proportional odds, adjacent categories, or other conditional models for ordinal responses. Simulations studies show that, for given sample sizes, the nominal and actual powers of the proposed test are similar.

Clinical Trials as Topic↗
PubMed2003

A simple method to estimate sample sizes for safety equivalence studies using inverse sampling.

Safety equivalence studies may be required to demonstrate that a new procedure or process is at least as safe as a previous one. They usually involve low or very low outcome rates that are often not precisely determined, making patient-based sample sizing uncertain. Using a reverse sampling approach, a method is derived from standard equations to estimate the number of events that need to be observed to demonstrate equivalence using the confidence interval approach. For instance, for a one-sided (nonsuperiority) hypothesis, 5% alpha risk, and 80% power, almost 100 events need to be observed in each study arm to demonstrate equivalence within 30%, or 250 events for 20% equivalence. The number of patients to be included can be derived directly from expected event rates.

Confidence Intervals↗
PubMed2005

Sample size computation for two-sample noninferiority log-rank test.

When an experimental therapy is less extensive, less toxic, or less expensive than a standard therapy, we may want to prove that the former is not worse than the latter through a noninferiority trial. In this article, we discuss a modification of the log-rank test for noninferiority trials with survival endpoint and propose a sample size formula that can be used in designing such trials. Performance of our sample size formula is investigated through simulations. Our formula is applied to design a real clinical trial.

Clinical Trials as Topic↗
PubMed2000

RSD requirement for different sample size for blend sampling.

A formula for calculating the equivalent relative standard deviation (RSD) for different sample sizes other than the Office of Generic Drugs (OGD) draft guidance was derived. These critical values vary with the population RSD and the sample size and guarantee the same confidence of passing a batch similar to the OGD blend uniformity test. Simulation results showed that the normal approximations give very close results to the simulation results. An assessment of the proposed OGD blend uniformity criteria against the first-stage USP content uniformity (CU) criteria for tablets was also made.

Drugs, Generic↗
PubMed2000

Adverse pregnancy outcome following post-chorionic villus sampling amniocentesis compared to chorionic villus sampling.

OBJECTIVE: To assess the adverse pregnancy outcome of post-chorionic villus sampling (CVS) amniocentesis and chorionic villus sampling. METHODS: Adverse pregnancy outcomes of 32 post-CVS amniocentesis cases and 264 CVS only cases were compared. The base-line characteristics were comparable in the 2 groups. RESULTS: One (3.1%) chromosomal abnormality was detected in the post-CVS amniocentesis group, compared to 5 (1.8%) in the CVS only group (p > 0.05). The fetal loss rate (spontaneous abortions and stillbirths) among continuing pregnancies was 3.2% in the post-CVS amniocentesis group and 3.5% in the CVS only group (p > 0.05). No statistically significant difference was found in the incidence of neonatal death, preterm delivery, fetal growth restriction, or congenital anomalies between the 2 groups. CONCLUSION: Adverse pregnancy outcome occurred at a similar frequency in the post-CVS amniocentesis group as in the CVS only group. Therefore, a subsequent amniocentesis after CVS can be considered as a safe procedure that does not introduce any additional adverse pregnancy outcome compared to that of CVS only.

Adult↗
PubMed1991

Antepartum fetal blood sampling with cordocentesis. Comparison with chorionic villus sampling and amniocentesis in diagnosing karyotype anomalies.

Cordocentesis under ultrasound guidance, or percutaneous umbilical blood sampling, was first reported in 1983 by Daffos et al. Since then the method has gained importance in prenatal diagnosis. In 1,011 cases at a women's clinic in Bonn, Federal Republic of Germany, 35% of the cordocentesis cases were done for blood group incompatibilities plus intravascular transfusion in most of the cases. In the remaining 65% the indications for cordocentesis were a rapid karyotype analysis, diagnosis of fetal infections and determination of fetal acid-base status in severe intrauterine growth retardation. Chorionic villus sampling (CVS) and amniocentesis were also performed to detect karyotype anomalies. Amniocentesis constituted 78.8% of the procedures and detected 50% of the karyotype abnormalities. Cordocentesis and CVS constituted 17.3% and 3.9%, respectively, of all the procedures and diagnosed 39% and 11%, respectively, of the abnormalities. Different forms of trisomy were the most common karyotype anomaly. Translocation was noted in 22 cases. Turner's, Klinefelter and triple X syndromes and triploidy were the next major forms.

Adult↗
PubMed1989

[Chorionic villi sampling. Results with the first 500 samples].

531 chorionic villi forceps biopsies were carried out, to look for genetic diseases. Sampling was impossible in 24 cases (4.5%). The following indications were chosen: maternal age over 38 years: 361 cases; parental chromosome abnormality: 28 cases; previous history of chromosome abnormality: 21 cases; X-linked disease: 77 cases; metabolic disease: 32 cases; hemoglobinopathy: 7 cases; blood group determination: 5 cases. An elective abortion was carried out in 44 cases (8.7%), whereas 465 pregnancies were not interrupted. Full term has been reached in 327 pregnancies. The rate of miscarriage in this group is 3.9% (13 miscarriages out of 327 pregnancies followed). The results obtained at the Saint-Vincent-de-Paul Hospital show that the cytogenetic technique is reliable, and that the low risk of sampling allows its application in the diagnosis of chromosome anomalies.

Adult↗
PubMed1967

Sample size and optimum sample design in tuberculosis surveys.

Tuberculosis surveys sponsored by the World Health Organization have been carried out in different communities during the last few years. Apart from the main epidemiological findings, these surveys have provided basic statistical data for use in the planning of future investigations. In this paper an attempt is made to determine the sample size desirable in future surveys that include one of the following examinations: tuberculin test, direct microscopy, and X-ray examination.The optimum cluster sizes are found to be 100-150 children under 5 years of age in the tuberculin test, at least 200 eligible persons in the examination for excretors of tubercle bacilli (direct microscopy) and at least 500 eligible persons in the examination for persons with radiological evidence of pulmonary tuberculosis (X-ray). Modifications of the optimum sample size in combined surveys are discussed.

Africa↗
PubMed2004

Comparison of sample preparation procedures for the determination of trace heavy metals in house dust, tobacco and tea samples by atomic absorption spectrometry.

The effect of wet ashing, dry ashing and microwave procedure for the determination of trace metal levels was investigated in house dust, tobacco and tea samples by atomic absorption spectrometry. The study of sample preparation procedures showed that the microwave method was the best. The recovery of trace metals was very good and precision and accuracy were compatible with standard reference material. The relative standard deviations for all measured metal concentrations were lower than 10%. The digestions of HNO3/H2SO4/HClO4 (4: 1: 1) mixture for house dust, HNO3/H2SO4/H2O2 (2: 2: 2) mixture for tea and HNO3/H2O2 (4: 2) mixture for tobacco were very efficient.

Dust↗