Uptake of particles by phagocytosing cells is a process that exhibits variability of its rate. This variability is inherent in the mechanism of particle uptake and in the mechanisms that determine ...the distribution of physiological states within a population of phagocytosing cells. When numbers of particles ingested by cells are determined flow cytometrically an additional measurement variability is superimposed on and interacts with the aforementioned biological variability. In one method of determining population phagocytosis parameters, which involves fitting theoretical equations to experimental time course data on the fractions of cells which have ingested 0, 1, 2, particles, the effects of measurement variability are circumvented, although this usually has the cost of not using all the sample data obtained. However, in a second, simpler, method which is based on determining the time course of the number of particles ingested by an average cell, measurement variability is not circumvented and its effects must be considered. An analysis of the combined effects of biological and measurement variability on the results obtained with the simpler method is presented in this paper. Experimental results for phagocytosis of latex microspheres of uniform size and fluorochrome content by populations of the ciliate Tetrahymena pyriformis show that, for this system, measurement variability is entirely negligible in comparison with biological variability. This conclusion might not apply to other systems, however, and situations which might make measurement variability of some significance are mentioned in the paper. The equations given can be used for the analysis of such situations.
A Bladder Cancer Flow Cytometry Network study has been carried out aimed at identification of the sources of inter‐ and intralaboratory variability. Replicate “cocktail” samples containing a mixture ...of peripheral blood lymphocytes and an aneuploid cell line and samples of peripheral blood lymphocytes serving as a DNA reference standard were distributed to five network laboratories. The samples were stained for DNA using propidium iodide, with each laboratory using its own staining protocol. Sets of these samples were analyzed by flow cytometry to obtain cellular DNA distributions. DNA index and hyperdiploid fraction were calculated for each histogram using an automated technique. Results were evaluated by analysis of variance to identify sources of variability. Three important sources of variation were found that affect flow cytometry in general and‐the transportability of flow cytometry results to routine clinical use in particular. The significant variation among laboratories that is constant across time most probably represents stable differences in instrumentation, instrument set‐up, and laboratory techniques. This variation can be compensated for, if it is known and stable, to develop transportable classification criteria. The second type of variation, termed the interaction component, represents differences among laboratories that are not constant across time. Sources of this variation include inconsistency in sample preparation, staining, and analysis. The elimination of this type of variation is required for meaningful comparison of data within and among laboratories and the creation of interlaboratory databases. The third type of variation represents pure measurement variability and affects the sensitivity of the technique.
This study evaluates changes over time in occupational exposure to n-hexane
by longitudinal repeated measurements analysis of data from the Biological
Monitoring Registry from 1991 to 1998. The main ...sources of variability in
n-hexane exposure among manufacturing workers in Florence province (Italy)
are inspected. The 2,5-hexanedione concentrations in urine of industrial workers are
explained by structural, individual and factory information. Here we analyse the
effectiveness of a 1994 law on workplace conditions based on variability
decomposition of measured 2,5-hexanedione concentrations.
We propose a hierarchical Bayesian model which takes into account the different
levels of aggregation of data. The results show that for leather and shoe factories,
the within-subject and within-factory variance components remain the most important
over the time of study, whereas the between-factory components decreased in
accordance with the expected effect of the new legislation.
Celotno besedilo
Dostopno za:
CEKLJ, DOBA, IZUM, KILJ, NUK, ODKLJ, OILJ, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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