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Results for “Sampling Errors”

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At least 55 records · Page 3Linked to original sources
PubMed1974

Fixed-ratio and fixed-interval schedule control of matching-to-sample errors by children.

Nine children, ages 4 through 7 yr, matched-to-sample on fixed-ratio, fixed-interval, variable-ratio, and variable-interval schedules of reinforcement. Simultaneous, zero-delay, and 2-sec delay matching were employed. Distributions of errors, in which the greatest number of errors occurred at the ordinal position immediately after reinforcement with fewer errors occurring at subsequent positions in the ratio, were produced by six of six children on fixed-ratio schedules for zero-delay and both of two children for 2-sec delay matching. Only two children of seven produced similar error distributions on simultaneous matching for fixed-ratio reinforcement. Variable-ratio schedules produced slightly lower accuracy for most subjects and no systematic error patterns for any subject. Error distributions occurred for all of the five children who experienced fixed-interval schedules for zero-delay matching. Peak error production occurred in the second fourth of the interval. Similar patterns were not produced on variable-interval schedules of equal reinforcement density. Schedule control of complex discriminated operants in children resembles control over similar responses of nonhuman animals.

Journal Article↗
PubMed1987

Heterogeneity of lung cancer: the problem of sample error in diagnostic electron microscopy.

We studied the ultrastructure of superficial and deep samples of 40 resected primary lung carcinomas. Tumour cell differentiation was semiquantitatively assessed and differences between samples of a same tumour were evaluated. In two instances were major differences in ultrastructural diagnosis found between the samples of the same tumour. A further 9 cases showed one predominant differentiation in one sample, but two equally predominant differentiations in the second sample. The other 29 tumours did show occasional minor differences between the samples, but these differences did not result in differences in ultrastructural diagnosis.

Carcinoma, Small Cell↗
PubMed1984

Estimation of sampling errors in a high-resolution TV microscope image-processing system.

The basic postulate of this paper is that the commonly accepted sampling density of 2-4 pixels/micron in a high-resolution TV microscope system is too low to digitize exactly and analyze the complex cellular detail found in stained cell images. Depending on the specific microscope system, the required sampling density is much higher, lying between 15 and 30 pixels/micron. This sampling density is derived from the aliasing error, the resolution loss, and computational limitations. The mathematical and optical methods and equipment used to obtain these results are described in detail.

Analog-Digital Conversion↗
PubMed1998

Sampling errors in projection reconstruction MRI.

Certain kinds of artifacts have been reported when projection reconstruction (PR) techniques are used in magnetic resonance imaging (MRI). These will occur if the spacing between samples in k-space is too large. It has been suggested that PR requires finer k-space sampling than does two-dimensional Fourier reconstruction, and that the usual Nyquist criterion is inadequate. This paper examines this problem, with the conclusion that the Nyquist sampling criterion is adequate to avoid aliasing effects, provided that a band-limited interpolation is used in k-space. This procedure is motivated by analysis of the PR technique as it is commonly implemented in x-ray computed tomography. A related problem is shown to be the construction of a filter function in k-space that gives proper weight to the low spatial frequencies. It is shown that a simple ¿k¿ filter does not satisfy this requirement, and a procedure for deriving a suitable filter is described. The methods are tested in simulated PR profiles of circular disks of two different sizes. It is shown that the combination of the two new methods gives virtually perfect reconstruction for disks up to the size implied by the Nyquist limit.

Algorithms↗
PubMedDate not supplied

Computer-assisted human semen analysis. Sampling errors and reproducibility.

Videomicrographic computer-automated semen analysis systems allow quantitative description of sperm motility, velocity, progression, and head movement amplitude and frequency with unprecedented ease. The minimum number of spermatozoa needed for stable results, the variability of measurements and optimum methods of sampling the ejaculate were determined for one such system (Cell-Soft, CRYO Resources, New York, NY). Sampling a minimum of 225 spermatozoa yields stable measurements, and analyzing four microscope fields in triplicate provides data with the lowest coefficient of variation. The variability attributable to the instrument itself was acceptable for all measurements (6.2% to 15.4%) except mean amplitude of lateral head displacement. Limitations of these results and the potential utility of videomicrographic sperm movement analysis are discussed.

Electronic Data Processing↗
PubMedDate not supplied

Fetoscopy and fetal blood sampling in the management of a twin pregnancy with 45,X/46,XX amniotic fluid cell mosaicism and a suspected fluid sampling error.

A 37 year-old woman with a twin pregnancy underwent amniocentesis to exclude fetal chromosome abnormality. The results indicated that both fetuses were mosaics, with 45,X and 46,XX, cell lines. Since it was suspected from the ultrasound scan that the twins were dizygotic, the result was questioned. Fetoscopy and fetal blood sampling were performed and karyotyping the fetal lymphocytes confirmed that one twin was indeed a mosaic, 45,X/46,XX, but the other had a normal male chromosome complement. The pregnancy resulted in the birth of a phenotypically normal girl, in whom the 45,X/46,XX mosaicism was confirmed, and a normal boy.

Adult↗
PubMed1980

Observation procedure, observer gender, and behavior valence as determinants of sampling error in a behavior assessment analogue.

Several factors thought to influence the representativeness of behavioral assessment data were examined in an analogue study using a multifactorial design. Systematic and unsystematic methods of observing group behavior were investigated using 18 male and 18 female observers. Additionally, valence properties of the observed behaviors were inspected. Observers' assessments of a videotape were compared to a criterion code that defined the population of behaviors. Results indicated that systematic observation procedures were more accurate than unsystematic procedures, though this factor interacted with gender of observer and valence of behavior. Additionally, males tended to sample more representatively than females. A third finding indicated that the negatively valenced behavior was overestimated, whereas the neutral and positively valenced behaviors were accurately assessed.

Journal Article↗
PubMed1996

Sampling error in small-bore sheathless capillary electrophoresis/electrospray-ionization mass spectrometry.

Two previously unreported sources of systematic error in electrokinetic injection caused by induced (hydrodynamic) flow in sheathless capillary electrophoresis/electrospray have been characterized for an interface constructed from 5 microns i.d. capillary column(s) with a 2-5 microns i.d. electrospray tip(s). The tip of a sheathless interface is usually exposed to the atmosphere, resulting in evaporation of buffer solvent and inducing flow inside the column; such flow can cause a significant underestimation of injection size for quantitative electrokinetic sampling by as much as 50%. This bias can be eliminated during the injection process by temporarily immersing the tip in buffer solvent. The second source of hydrodynamic flow results from the electrostatic pull exerted by the electrospray process on the buffer, reducing migration times. Reduction in migration times causes an overestimation of sampling volume if there are no electrospray processes during the sampling event. The magnitude of this effect is a complex function of electrophoretic and electrospray parameters and has been measured to be as high as 15% for 5 microns i.d. capillaries. The possible deterioration of electrophoretic resolution caused by these processes is not yet clarified.

Animals↗
PubMed1989

Discrepancies in ploidy determination due to specimen sampling errors.

Two techniques are described to enhance the detection of low frequency aneuploid cells in automated cell analysis. One method concerns a cell preparation technique; the other is focused on specific cell selection at the measurement level. The cell preparation method has been designed to select and process the tumour areas in paraffin blocks and can be used for image as well as for flow cytometry. The technique uses incident fluorescence microscopy for visual inspection of the surface of the fluorescently stained tissue block to select the specific tumour parts. Using image cytometry, it is shown that in tissue sections with very small tumour foci and many normal cells, aneuploidy could only be detected after enrichment of the cell sample with the specifically selected areas. The cell selection at the measurement level is directed towards detection of low frequency aneuploid cells on microscope slides using the specific capacities of LEYTAS (Leyden Television Analysis System). With this system, cells of interest can be selected by means of minimum size and intensity thresholds. In addition to measurement of the total cell population, all cells above a minimum DNA value can thus be specifically selected and measured. The advantage of both enrichment techniques is the possibility to detect and measure aneuploid cell lines in cases where normal, diploid cells dominate the paraffin tissue.

Aneuploidy↗
PubMed1989

Campylobacter pylori infection in biopsy specimens of gastric antrum: laboratory diagnosis and estimation of sampling error.

Campylobacter pylori infection was sought in 382 consecutive patients referred for upper gastrointestinal endoscopy. Five antral biopsy specimens were taken from each patient: one was inserted into a CLO-test to detect the urease activity of C pylori, two were sent for histological analysis where multiple sections were stained by the Warthin-Starry silver method, and two were sent for microbiological evaluation by Gram stain and culture. A patient was deemed to be infected when C pylori was cultured or seen in either the histological sections or the Gram stain of the biopsy smear. One hundred and seventy four (46%) patients were infected. Culture, Gram stain, histological examination and the CLO-test showed sensitivities of 92%, 87%, 93% and 90%, respectively. In 27 (15%) infected patients an uneven distribution of C pylori was seen between samples in the biopsy pair sent for histology. Examination of multiple sections stained with Warthin-Starry silver was more sensitive at detecting infection (93%) than examination of multiple sections from only one biopsy specimen (84%). Fifty seven of 80 patients, biopsied a median seven days (range 5 to 55) after completing colloidal bismuth subcitrate treatment, were still infected with C pylori. There was no decrease in the sensitivities of the above tests to detect infection after treatment. It is concluded that at least two antral biopsy specimens should be examined when attempting to diagnose C pylori infection by histological methods.

Biopsy↗