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At least 1,315 records · Page 73Linked to original sources
PubMed1984

Computerized histopathologic assessment of malignant potential. III. Refinements of measurement and data analysis.

The nucleolar area of uveal melanomas, measured from standard hematoxylin-and-eosin-stained microslides , has been shown in previous work to correlate well with survival following enucleation of the tumor-bearing eye. Despite this correlation, the accuracy of the original system for measuring nucleolar area was affected by several sources of error: (1) the algorithm by which area was computed underestimated true area, (2) geometric and optical factors caused overestimation of nucleolar area unless measured in the center of the microscopic field of view and (3) the area of small nucleoli, as the result of several possible mechanisms, contains less useful information than the area of large nucleoli. This paper presents methods introduced to reduce error from these sources and demonstrates that the predictive value of nucleolar measurements is relatively insensitive to high levels of random variation.

Cell Nucleolus↗
PubMed1981

Sample viscosity can be a source of analytical error when discrete sampler-dilutors are used.

Total protein concentration in the serum of a patient with hyperviscosity syndrome differed as measured by the biuret procedure in the DuPont aca (80 g/L) and the SMA 12/60 (105 g/L), owing to viscosity-dependent errors with the aca sampling system; the magnitude depended on sample temperature and volume of sample aspirated. This kind of error was not observed with the SMA 12/60 and was far less severe when a Micromedic sampler-dilutor was tested. It could be eliminated in the case of the aca by adding sample to test packs with a syringe rather than with the aca automated sampler-dilutor. We thus recommend use of the syringe method when unusually viscous samples (serum or other body fluids) are analyzed in the aca.

Autoanalysis↗
PubMed1977

[Sources of several errors in DNA cytofluorimetry].

It was shown that serious errors in DNA cytofluorimetry may be due to incorrect illumination of photocathode of the photomultiplier in the cytofluorimeters and non-observance of the requirements to the nuclear structures of the cells under measurement with respect to their chemical integrity and thickness. The methods of the optimal illumination of photocathode in the cytofluorimeters and the criteria of selection of the nuclear structures on slides are considered with the aim of obtaining the objective results of DNA cytofluorimetry.

DNA↗
PubMed1997

[Normal anatomy and pathologic features of the supraspinatus muscle: comparison between ultrasonography and surgery. Analysis of the potential sources of diagnostic errors].

The supraspinatus muscle performs about 60% of the elevation-abduction motion of the arm; therefore, it has a prominent functional role among the extrarotational muscles of the shoulder and is the most injured in subacromial space conditions. Seventy-four patients, aged 21-64 years, were examined to compare ultrasonography (US) results with surgical findings in supraspinatus conditions and to analyze the possible pitfalls in US diagnosis. All the patients underwent conventional X-ray, US and then surgery or arthroscopy. The following criteria were considered: morphology, thickness, echotexture, the convexity of the superior border of supraspinatus tendon, the relationships with the subacromial bursa and the tendon of the biceps long head, the regularity of the bone cortex of the humeral head. US showed: chronic degenerative tendinopathy in 10 patients; perforating focal injuries in 21 patients; deep focal injuries in 10 patients; intramural focal injuries in 6 patients; superficial focal injuries in 8 patients; complete tendon tear with detachment in 19 cases. 62/74 US diagnoses were surgically confirmed, with a specificity of 83.7%. In our experience, US provided very useful information about the pattern, size and site of the injuries and was very helpful in the surgical planning.

Adult↗
PubMed1997

Chronic granulomatous disease masquerading as a bladder tumor: a potential source of diagnostic error.

Chronic granulomatous disease (CGD) is a rare inherited disease of childhood, characterized by recurrent bacterial or fungal infections. The underlying defect is a dysfunction of neutrophil granulocytes interfering with their ability to kill phagocytosed microorganisms. Genitourinary tract involvement has been reported in 38% of these patients. We report a case of CGD in whom the most important findings were urinary bladder tumors at different locations and a subsequent obstruction of the left ureter. A review of the pathogenesis of the disease, potential involvement of the urinary tract and treatment is presented.

Adult↗
PubMed2006

Errors of Mueller matrix measurements with a partially polarized light source.

The linear errors of Mueller matrix measurements, using a partially polarized light source, have been formulated for imperfections of misalignment, depolarization, and nonideal ellipsometric parameters of the polarimetric components. The error matrices for a source-polarizer system and a source-polarizer-compensator system are derived. A polarized light source, when used with an imperfect polarizer, generates extra errors in addition to those for an unpolarized source. The compensator redistributes these errors to different elements of the error matrix. The errors of the Mueller matrices for the polarizer-sample-analyzer and the polarizer-compensator-sample-analyzer systems are evaluated for a straight through case. This error analysis is applied to a Stokes method and an experiment was performed to show the errors by a polarized light source. This general analysis can be used to evaluate errors for ellipsometry and polarimetry.

Journal Article↗
PubMed2004

Correcting confocal acquisition to optimize imaging of fluorescence resonance energy transfer by sensitized emission.

Imaging of fluorescence resonance energy transfer (FRET) between suitable fluorophores is increasingly being used to study cellular processes with high spatiotemporal resolution. The genetically encoded Cyan (CFP) and Yellow (YFP) variants of Green Fluorescent Protein have become the most popular donor and acceptor pair in cell biology. FRET between these fluorophores can be imaged by detecting sensitized emission. This technique, for which CFP is excited and transfer is detected as emission of YFP, is sensitive, fast, and straightforward, provided that proper corrections are made. In this study, the detection of sensitized emission between CFP and YFP by confocal microscopy is optimized. It is shown that this FRET pair is best excited at 430 nm. We identify major sources of error and variability in confocal FRET acquisition including chromatic aberrations and instability of the excitation sources. We demonstrate that a novel correction algorithm that employs online corrective measurements yields reliable estimates of FRET efficiency, and it is also shown how the effect of other error sources can be minimized.

Algorithms↗
PubMed1994

Validation of the doubly labeled water method in growing pigs.

The CO2 production (rCO2) of eight growing pigs was determined by continuous collection of CO2 over 21 days and simultaneously estimated using the doubly labeled water (DLW) method. The aim was to assess the accuracy of the method before and after correction for known sources of error and to test for any residual discrepancy arising from as yet unidentified sources of error. Mass spectrometer accuracy was verified by analyzing serial dilutions of the dose material in the form of an artificial decay curve; no significant bias was detected. The physiological errors were linearly dependent on weight gain. DLW-derived rCO2 (corrected only for fractionated water loss) underestimated the true value by 0.270 l CO2/g wt gain or -8% in the restricted (group R) and -16% in the ad libitum-fed (group AL) groups. Known sources of error accounted for -0.006 (methane), -0.032 (fecal 2H losses), -0.108 (fat synthesis), and -0.146 (changing pool size) l CO2/g wt gain. After correction for these sources of error the DLW-derived rCO2 differed from the true value by -2 +/- 3% in group R and 0 +/- 3% in group AL. Thus there was no significant bias in the DLW method after correction for known sources of error, even during rapid weight gain or at weight stability with or without correction. The precision estimates include both dose and background errors and uncertainty in the correction factors used. Strategies for optimizing precision are presented.

Animals↗
PubMed1988

Methodological errors in radioisotope flux measurements.

We examined several sources of error in isotopic flux measurements in a commonly used experimental model: the study of 22Na and 36Cl fluxes across rat ileal tissue mounted in the Ussing flux chamber. The experiment revealed three important sources of error: the absolute counts per minute, the difference in counts per minute between serial samples, and averaging of serial samples. By computer manipulation, we then applied hypothetical changes in the experimental protocol to generalize these findings and assess the effect and interaction of the absolute counts per minute, the sampling interval, and the counting time on the magnitude of the error. We found that the error of a flux measurement will vary inversely with the counting time and the difference between the consecutive sample counts per minute used in the flux calculations and will vary directly with the absolute counts per minute of each sample. Alteration of the "hot" side specific activity, the surface area of the tissue across which flux is measured and the sample volume have a smaller impact on measurement error. Experimental protocols should be designed with these methodological considerations in mind to minimize the error inherent in measuring isotope flux.

Animals↗
PubMed2003

Quantifying errors without random sampling.

BACKGROUND: All quantifications of mortality, morbidity, and other health measures involve numerous sources of error. The routine quantification of random sampling error makes it easy to forget that other sources of error can and should be quantified. When a quantification does not involve sampling, error is almost never quantified and results are often reported in ways that dramatically overstate their precision. DISCUSSION: We argue that the precision implicit in typical reporting is problematic and sketch methods for quantifying the various sources of error, building up from simple examples that can be solved analytically to more complex cases. There are straightforward ways to partially quantify the uncertainty surrounding a parameter that is not characterized by random sampling, such as limiting reported significant figures. We present simple methods for doing such quantifications, and for incorporating them into calculations. More complicated methods become necessary when multiple sources of uncertainty must be combined. We demonstrate that Monte Carlo simulation, using available software, can estimate the uncertainty resulting from complicated calculations with many sources of uncertainty. We apply the method to the current estimate of the annual incidence of foodborne illness in the United States. SUMMARY: Quantifying uncertainty from systematic errors is practical. Reporting this uncertainty would more honestly represent study results, help show the probability that estimated values fall within some critical range, and facilitate better targeting of further research.

Bias↗
PubMedDate not supplied

Errors in plasma creatine kinase estimations on fetal blood samples resulting from contamination with amniotic fluid and maternal blood: relevance for the prenatal diagnosis of Duchenne muscular dystrophy.

This paper presents a detailed analysis of the calculation of fetal plasma CK activity in fetal blood samples contaminated with amniotic fluid and maternal blood. The seemingly simple formula for this calculation, first presented by Mahoney et al. (1977), is actually more complex than it appears; values for up to nine variables, two of which can only be assumed, are needed. Small variations in certain variables may result in very large errors in the final calculated value of fetal plasma CK activity. Examples of diluted blood samples are considered and the effects of allowing for reasonable errors in the variables is explored. The main source of error is in the measurement of CK activities in the diluted blood sample and in the amniotic fluid. Contamination by blood originating from the maternal circulation can also be a large source of error, especially if the mother is a carrier of DMD and maintains a high level of plasma CK activity during pregnancy. Fetal blood indices have to be assumed; these may be a source of significant error, depending on the difference between the actual and assumed values. The measurement of fetal plasma CK activity by the indirect calculation method is discussed in the context of the prenatal diagnosis of DMD.

Amniocentesis↗