SEARCH · PubMed Health

Results for “Sampling Errors”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources

PubMed1985

Time sampling and measurement error: the effect of interval length and sampling pattern.

The accuracy of momentary time-sampling was evaluated for behaviors occurring for different proportions of time, for different momentary time-samples and for sessions of different lengths. For 1-hr sessions, momentary time-samples of 10, 20 or 30 see intervals between observations yielded 90% of estimates within 10% of the comparison standard, for behaviours of 25%, 50% and 70%. Behaviours occurring for 2% of the session were not accurately recorded even at 10-sec momentary time-samples. For a 5-min momentary time-sample, this criterion was only approached when 8 hr data was averaged to give a single score for each individual, for behaviours of 25% or more. The 5-min momentary time-sample was also compared with a 1 in 5-min cluster sample; although less accurate, cluster-sampling might be a useful strategy in some settings.

Behavior↗

PubMed1983

Adaptive control of theophylline therapy: importance of blood sampling times.

A two-observation protocol for estimating theophylline clearance during a constant-rate intravenous infusion is used to examine the importance of blood sampling schedules with regard to the information content of resulting concentration data. Guided by a theory for calculating maximally informative sample times, population simulations are used to assess the effect of specific sampling times on the precision of resulting clearance estimates and subsequent predictions of theophylline plasma concentrations. The simulations incorporated noise terms for intersubject variability, dosing errors, sample collection errors, and assay error. Clearance was estimated using Chiou's method, least squares, and a Bayesian estimation procedure. The results of these simulations suggest that clinically significant estimation and prediction errors may result when using the above two-point protocol for estimating theophylline clearance if the time separating the two blood samples is less than one population mean elimination half-life.

Blood Specimen Collection↗

PubMed1998

Detection of occult breast cancer micrometastases in axillary lymph nodes using a multimarker reverse transcriptase-polymerase chain reaction panel.

BACKGROUND: Axillary lymph node status in breast cancer patients remains the single most important predictor of outcomes. Current methods of histopathologic analysis may be inadequate because 30% of node-negative patients recur. The purpose of this study was to test the hypothesis that a multigene reverse transcriptase-polymerase chain reaction (RT-PCR) panel provides a more sensitive method to detect axillary lymph node metastases than routine pathologic examination. STUDY DESIGN: Sixty-one consecutive breast cancer patients were evaluated, with nine normal control patients. Nodes > 1 cm were bisected for histopathologic and RT-PCR analysis. Nodal tissue was homogenized, and total RNA was converted into cDNA with reverse transcriptase. Reverse transcriptase-polymerase chain reaction analysis was performed with primers specific for keratin-19, c-myc, prolactin inducible protein (PIP), and beta-actin using ethidium bromide gel electrophoresis. Reverse transcriptase-polymerase chain reaction positive/ pathology negative axillary lymph nodes were reevaluated using step sectioning and immunohistochemical staining. RESULTS: Thirty-seven patients had pathologically negative axillary lymph nodes, of which 15 (40%) were positive by RT-PCR analysis. Two RT-PCR negative results (one probably from tissue processing error and the other secondary to sampling error) among the 24 histologically positive specimens were detected (8%). The number of patients in each pathologic stage was 26 patients in stage I; 18, stage IIA; 7, stage IIB; 7, stage IIIA; 3, stage IIIB; and 0 patients in stage IV. By RT-PCR staging, 8 of 26 patients went from stage I to IIA (30%), and 7 of 18 from stage IIA to IIB (39%). Of the RT-PCR positive individuals who were stage I by pathologic analysis, 100% were found to be c-myc positive, 0% keratin-19 positive, and 0% PIP positive; for stage IIIB patients these markers were 50%, 100%, and 100% respectively. Additionally, an increasing number of positive markers per specimen appeared to correlate with larger primary tumor size (p < 0.01) and decreased predicted 5-year survival (r = 0.950, p < 0.002). CONCLUSIONS: Multimarker RT-PCR analysis appears to be a readily available and highly sensitive method for the detection of axillary lymph node micrometastases. Longterm followup of RT-PCR positive patients will be required to determine its clinical relevance. If validated as a predictor of disease recurrence, this method would provide a powerful complement to routine histopathologic analysis of axillary lymph nodes.

Axilla↗

PubMed1988

Comparison of two techniques for obtaining samples for coagulation studies: venipuncture and intraarterial line.

The purpose of this study was to compare blood coagulation values drawn by venipuncture and from an intraarterial catheter. A 10 ml discard was obtained from 50 consecutive patients before obtaining the coagulation sample from the intraarterial catheter, and a 0.5 ml discard was obtained from the venipuncture specimen. A two-tailed t test for related samples was performed. The results revealed no significant difference between the two methods (p less than 0.05). The small differences seen were attributed to sampling error. These results suggest that blood samples obtained from heparinized intraarterial catheters after a 10 ml discard provide an accurate assessment of patients' mean clotting time.

Adult↗

PubMed1983

Analysis of polymorphic variation in different types of habitat.

A correlation between the distribution of an organism and features of its environment can be taken as indirect evidence of natural selection. Biologists may therefore collect samples from polymorphic populations at a number of locations, classify the locations into habitat types, and consider whether the distribution of morphs varies with the habitat. Statistical aspects of this type of study are discussed in this paper. A randomization test for habitat effects is proposed and a negative binomial model is suggested for the distribution of morphs from random locations within one type of habitat. Data on the distribution of Cepaea hortensis and C. nemoralis snails in southern England provide an example. For both species there is clear evidence of differences between habitats, although the morph distributions are rather variable within habitats. The negative binomial model suggests that, for the snail data, variation in morph proportions is mainly due to location differences. The binomial sampling error is relatively unimportant unless the sample size at a location is very small. Therefore it is reasonable to analyse morph proportions by standard methods without giving different weights to data from different locations. The snail data are analysed in this way. Discriminant function analyses are used to test for habitat effects. The relationships between C. hortensis and C. nemoralis morph frequencies within one habitat are examined by a canonical correlation analysis.

Animals↗

PubMed1999

Equivocal diagnoses in breast aspiration biopsy cytology: sources of uncertainty and the role of "atypical/indeterminate" terminology.

In 1996, a National Cancer Institute committee recommended four categories as uniform terminology for breast fine-needle aspirations (FNAs): benign, malignant, suspicious/probably malignant, and atypical/indeterminate. The latter is a controversial category. This study evaluates the usefulness of the atypical/indeterminate term, and examines sources of diagnostic equivocation in breast FNA. Eight hundred and twenty-two consecutive breast FNAs were previously classified as benign, malignant, suspicious, or unsatisfactory. Two hundred and thirteen (25.9%) cases had surgical follow-up and were classified as true positive (TP), false positive (FP), true negative (TN), false negative (FN), true suspicious (TS), or false suspicious (FS). Slides from FN, FP, TS, and FS were reviewed for interpretative error, poor clarity or preservation, obscuring material, sampling error, or insufficient malignant criteria. Cases were also evaluated as to whether classification as "atypical/indeterminate" would have improved patient care. There were 21/822 (2.6%) FN, 37/822 (4.5%) TS + FS, and 0 FP diagnoses. Seventy percent of suspicious diagnoses showed cancer on follow-up. The majority of FN and suspicious cases were due to sampling problems and insufficient criteria of malignancy. None were deemed more appropriately classified as "atypical/indeterminate" All required surgical confirmation for treatment. All equivocal breast diagnoses are due to similar problems. Splitting them into "suspicious/probably malignant" and "atypical/indeterminate" would not lower the biopsy rate. A simpler three-part terminology of benign, malignant, and suspicious/equivocal, without qualification of the latter favoring benign or malignant, would provide more effective communication and appropriate follow-up. Diagn. Cytopathol. 1999;21:217-222.

Biopsy, Needle↗

PubMed1982

Tissue diagnosis for carcinoma of the pancreas and periampullary structures.

In a county hospital, 217 patients were operated on for suspected cancer of the pancreas (186 patients) and periampullary structures (31 patients). The surgeons' philosophy was to avoid biopsy of the pancreas whenever possible, they often performed radical resection based on clinical judgment alone (8% of the resections were chronic pancreatitis). Follow-up of the 65 patients who were presumed to have carcinoma without histologic proof showed the surgeon's clinical diagnosis to be incorrect in over 7% of the cases (maximum error - 18%). Among patients with carcinoma of the pancreas, one third of the pancreatic biopsies missed the lesion (surgeon's sampling error). Frozen section examination of pancreatic biopsies in 63 patients showed false positive and negative rates of 3% and 4%, respectively (pathologist's sampling or interpretation errors). Two of 31 incisional biopsy of the pancreas resulted in pancreatic fistula; none of 24 needle biopsies did. Otherwise, biopsy of the pancreas did not influence mortality or morbidity after either resection or bypass procedures.

Acute Disease↗

PubMed1988

Stability of arterial concentrations during continuous inhalation of C15O2 and 15O2 and the effects on computed values of CBF and CMRO2.

Stability of arterial whole blood and plasma concentrations is a basic requirement in the application of the oxygen-15 (15O2) steady-state inhalation technique for measuring regional cerebral blood flow and oxygen use. The level of stability obtainable in practice is reported in the form of retrospectively analysed blood data from 626 consecutive studies in patients with a range of clinical conditions. Serial arterial whole blood and plasma concentrations were measured during both C15O2 and 15O2 inhalations, and coefficients of variation were calculated. In addition, these concentrations were compared with the corresponding values recorded at the start of each study and maximum variations were calculated. For all four concentrations, mean and median coefficients of variation were around 5 and 4%, respectively. Mean and median maximum variations were around 9 and 7%, respectively. The effects of these variations on the calculations of regional cerebral blood flow, oxygen extraction, and oxygen use were estimated. Mean expected errors were found to be between 4 and 9%, and median expected errors between 3 and 6%. Inherent blood sampling errors were assessed from blood volume studies using 11CO-labeled red cells. These errors were found to be less than 3%.

Arteries↗

PubMed1999

Management of nonspecific low back pain by physiotherapists in Britain and Ireland. A descriptive questionnaire of current clinical practice.

STUDY DESIGN: A descriptive questionnaire of chartered physiotherapists. OBJECTIVE: To investigate current physiotherapeutic management of low back pain throughout Britain and Ireland. SUMMARY OF BACKGROUND DATA: Physiotherapists play a key role in low back pain management. Although clinical guidelines for best practice have been developed recently, there has been no large-scale attempt to describe current physiotherapeutic treatment approaches within Britain or Ireland. METHODS: After semi-structured interviews (n = 6) and two pilot studies (n = 77) were done, postal questionnaires were distributed to four regional cluster samples of the membership of two physiotherapy professional organizations (n = 2654). After two mailings, a random sample of 90 nonresponders were followed up. Data were analyzed using the Statistical Package for the Social Sciences (SPSS Ltd., Woking, Surrey, UK), and precision of the survey estimates was assessed by calculation of sampling errors and intraclass correlation coefficients for cluster sampling. RESULTS: Results were received from 1548 therapists (total response rate, 58.3%); of these, 813 reported that they were practicing in settings in which they treated patients with low back pain. Analysis of the results indicated the overall popularity of the Maitland mobilization and McKenzie approaches among physiotherapists. Although exercise per se was mentioned frequently by respondents, a marked difference in opinion among therapists regarding the optimal type of exercise for low back pain was obvious. Little evidence was demonstrated of the use of manipulation, fitness programs, or multidisciplinary efforts involving behavioral and physical aspects of treatment. Commonly used methods of electrotherapy were interferential therapy, ultrasound, pulsed short-wave diathermy, and transcutaneous electrical nerve stimulation. CONCLUSIONS: The results of this study emphasize the need to evaluate further and improve the dissemination of findings regarding the effectiveness of specific physiotherapy approaches for low back pain management.

Adult↗

PubMed1997

An estimation of the size distribution of amalgam particles in dental treatment waste.

Regulations have been adopted in several countries of the European Union which prescribe that dental treatment waste water must be discharged via an amalgam separator device. Since the effectivity of the device strongly depends on the size of the amalgam waste particles, this size was evaluated in waste water samples from eight dental offices. Per sample, all solid particles were separated from the waste water by pressure filtration, then dried and divided into six fractions by being sieved over five sieves with decreasing mesh width. Of the particles in each fraction, the density was determined by picnometry, the mass by weighing, and the area and width by image analysis. For this analysis, width was defined as the dimension perpendicular to the length of the particles. By combining the density, area, and width determinations of all fractions, we obtained mass distributions per waste particle width of the samples. The proportional amalgam mass of the distributions was estimated with the measured density of the particle fractions and with a number of assumptions for the density of amalgam particles only and of other waste particles only. Each waste sample has its own characteristics with respect to the mass and density of the particle fractions. The size distribution of waste particles has a bimodal shape and consists of a distribution of small (width, 2 to 90 microns) and large particles (width, 160 to 5500 microns). For small particles with a width up to 60 microns, the influence of the assumptions on the estimation of the proportion amalgam of the waste mass distribution is minor when compared with the sampling error. By averaging the estimations over the samples, one can estimate the weight of amalgam particles with a width < 10 microns and < 50 microns, respectively, between 4 and 15% and between 15 and 30%. The smallest particles comprising 5% of the amalgam mass have an estimated width of up to 15 microns.

Dental Amalgam↗

PubMed1991

Accuracy of breast frozen section diagnosis in the community hospital setting: a detailed analysis of 628 cases.

The author presents a detailed analysis of 628 breast frozen sections performed at Columbia Hospital over a 35-month period. These 628 frozen sections came from a total of 574 females and 13 males (mean age 55.3 years and range 20.1 to 95.0 years). Frozen section diagnosis was deferred in 18 cases (2.8%) and diagnostic accuracy for presence or absence of malignant neoplasia was 99.2%; one false positive case (pathologist judgement error) and four false negative cases (two sampling errors and two pathologist judgement errors) were detected. Strict diagnostic accuracy for this series was 98.7%. Fifty-three of 223 positive frozen sections (23.8%) were immediately followed by completion mastectomy. The author discusses the philosophy of frozen section technique and concludes that breast frozen section analysis in a busy community hospital setting can meet and even exceed the accuracy level attained at large academic medical centers.

Adult↗

PubMed1982

Paired cervical smears: a method of reducing the false-negative rate in population screening.

Cervical smears taken by the wooden Ayre spatula (widely used in the United Kingdom) and by a plastic spatula (Armovical) were compared for their ability to detect dysplastic cervical epithelium and endocervical cells. At the same time, the value of taking duplicate smears was assessed. Paired cervical smears were obtained at a single attendance from 21,352 women, using the 2 types of spatulas in 4 different sequences. Although individually the Armovical proved superior to the Ayre spatula for the collection of endocervical epithelial material, this advantage was not complemented by any marked improvement in its detection of cervical dysplasia. Paired smear sampling, however, was clearly more rewarding in this respect and also allowed the introduction of laboratory quality control, as each preparation of any given pair was examined by a different screener. The false-negative rate was 18.5%: it comprised 11.1% sampling error and 7.4% screening error. It is concluded that paired smear sampling in population screening would significantly reduce the false-negative rate.

Carcinoma in Situ↗

PubMed1987

Problems with measurements caused by high concentrations of serum solids.

There have been numerous reports of spectrophotometric and volume problems caused by elevated levels of lipids in blood. The offending lipids, primarily triglycerides, not only cause turbidity leading to optical aberrations when added to analytical reagents, but also result in short-sampling errors leading to the measurement of inaccurate volumes of sample. Numerous methods have been developed to clear the lipemia, including ultracentrifugation organic solvent extraction, chemical precipitation and, most recently, enzymic hydrolysis. Although the latter procedures eliminate the optical problems, they do not deal with the volume dilution error created by the triglycerides. In turn, corrective mathematics have been developed to compensate for the inaccurate pipetting caused by the elevated lipids in a sample; however, these empirical calculations are not truly accurate at high concentrations of total lipids. This monograph will describe the problems caused by the presence of elevated lipids and the means available for treating them.

Blood Chemical Analysis↗

PubMed1992

Detection of cytomegalovirus (CMV) in granulocytes by polymerase chain reaction compared with the CMV antigen test.

To compare the sensitivity and suitability of detection of active cytomegalovirus (CMV) infection by using monoclonal antibodies against CMV antigen (antigen test to detect antigenemia) and the polymerase chain reaction (PCR; to detect viral DNA) in granulocytes, 19 heart and 2 lung transplant recipients were closely monitored by these tests for at least 3 months after transplantation. All patients were CMV seropositive or had a seropositive donor. In total, 201 samples were tested; 46 were positive by both tests, 9 samples showed only antigenemia, 54 samples were positive by PCR only, and 102 samples were negative by both tests. PCR was positive earlier after transplantation in eight patients, whereas antigenemia was positive earlier after transplantation in one patient. In another four patients, both tests were positive at the same time. PCR was, on average, positive for a longer period of time. Discordant results showing a positive antigen test and a negative PCR were partly due to sampling error; some were positive by PCR on retesting. Samples which were negative by the antigen test and positive by PCR were taken at the beginning or at the end of an active CMV infection. In two patients, no active CMV infection was detected by the antigen test, cultures of urine and saliva, or serology, although PCR was positive for a long period of time in the two patients.

Antigens, Viral↗

PubMed1989

Use of a laser diffraction particle sizer for the measurement of mean diameter of multicellular tumor spheroids.

Increasing use is being made of tumor cell lines cultured as cell aggregates (generally referred to as multicellular spheroids) in in vitro radiosensitivity and/or chemosensitivity tests. Conventional procedures for the determination of mean spheroid diameters for the construction of growth delay curves employ a microscope-image analyzer. However, this approach can prove excessively time consuming when large numbers of samples have to be measured. We have, therefore, been exploring the use of a Laser Diffraction Particle Sizer, the Malvern 2600 long bench model, for the measurement of mean spheroid diameter and size distribution. We report here a direct comparison between measurements carried out by the instrument and under the microscope. Also a comparison of growth curves for six cell lines constructed from measurements by the microscope and by the instrument. A number of factors that might affect the accuracy of spheroid diameter measurement by the instrument have been investigated: The effect of stirring to maintain the spheroids in suspension during measurement. Sampling error due to removal of a series of spheroid samples from culture flasks for measurement. Optimum numbers of scans to be carried out by the instrument to reach a constant value for mean diameter, and minimum SE of the mean.

Animals↗

PubMed1988

Estimation of allele frequencies at isoloci.

In some polyploid animals and plants, pairs of duplicated loci occur that share alleles encoding proteins with identical electrophoretic mobilities. Except in cases where these "isoloci" are known to be inherited tetrasomically, individual genotypes cannot be determined unambiguously, and there is no direct way to assign observed variation to a particular locus of the pair. For a pair of diallelic isoloci, nine genotypes are possible but only five phenotypes can be identified, corresponding to individuals with 0-4 doses of the variant allele. A maximum likelihood (ML) approach is used here to identify the set of allele frequencies (p, q) at the individual gene loci with the highest probability of producing the observed phenotypic distribution. A likelihood ratio test is used to generate the asymmetrical confidence intervals around ML estimates. Simulations indicate that the standard error of p is typically about twice the binomial sampling error associated with single locus allele frequency estimates. ML estimates can be used in standard indices of genetic diversity and differentiation and in goodness-of-fit tests of genetic hypotheses. The noncentral chi 2 distribution is used to evaluate the power of a test of apparent heterozygote deficiency that results from attributing all variation to one locus when both loci are polymorphic.

Alleles↗

PubMed1998

The uncertainty associated with the predictive value of test results.

The uncertainty associated with predictive value of test results was taken into consideration, as concerns both sampling error (related to the size of the statistical reference samples) and analytical imprecision (unavoidably involved by the measurement itself). A software package, developed for the statistical calculations, was used for the treatment of the results obtained for serum free thyroxin in euthyroid and dysthyroid subjects, assumed as an experimental model. Examples are shown for the obtainable functions predictive value vs. estimate and the related uncertainty regions. These data could help in comparing test results and, in particular, in preparing fully informative laboratory reports. The difficulties involved by an extensive application of the procedure are discussed.

Humans↗

PubMedDate not supplied

Platinum levels and clinical responses of tumours treated by cisplatin with and without concurrent hyperthermia: a case study.

The heterogeneity of platinum distributed within tissue after clinical administration of cisplatin was evaluated for the first time. Platinum levels were correlated with the observed clinical responses of separate superficial histiocytic sarcomas located in the forearm of a 74-year-old male patient. One of four lesions received four weekly treatments with hyperthermia administered concurrently with 30 mg/m2 cisplatin, while three lesions were treated with cisplatin alone. The lesion receiving hyperthermia concurrently with cisplatin had a solid partial response during a 6-week period following this therapy, whereas two other tumours receiving cisplatin alone progressed. One lesion could not be clinically evaluated. Platinum levels were determined in multiple samplings from three of the four lesions and normal tissue in order to evaluate the validity of taking a single tumour sample of 100 mg or less for the analysis of platinum content. Such a small single sample might provide a value significantly different from the true average because of sampling error. The range in platinum distribution encompassed an average of three-fold difference within eight separate sample groups, with a factor of six being the greatest difference in a single sample group. This degree of heterogeneity is great enough to suggest that conclusions made from the analysis of small and single random tissue samples could be sufficiently in error to misdirect investigative or medical decisions.

Aged↗