Coefficient of variation, for

When analysing the standard deviation value, which measures the dispersion of measurements, the effect of heteroscedasticity, already discussed in connection with the measurement of vapour pressure, is noted ie the dependency between standard deviation and average (the higher the average, the greater the dispersion of measurements). One way to make this unfortunate property obvious when it comes to analysing data is to calculate the coefficient of variation for each distribution (C 0- If it is more or less constant, there is heteroscedasticity. 

Berka et al [59] described an accurate and reproducible coulometric method, with chlorine electrogenerated at the anode, for the determination of micro quantities of primaquine phosphate. Titration was carried out in an anode compartment with a supporting electrolyte of 0.5 M sulfuric acid-0.2 M sodium chloride and methyl orange as indicator. One coulomb was equivalent to 1.18 mg of primaquine phosphate. The coefficients of variation for 0.02-0.5 mg of primaquine phosphate were 1-5%. Excipients did not interfere. 

These biosensors were tested for glucose and lactate measurements in sera, and for lactate measurements in whey solutions. Good agreements were obtained between the present method and reference methods. For glucose analysis in serum, the coefficient of variation for 53 repeated measurements performed over a 10 h period was 4.8% while for lactate analysis, 80 assays performed over a 15 h period gave a coefficient of variation of 6.7%. Thus,... 

The overall average values and coefficients of variations for model... 

Rao et al.20 demonstrated a fluorescence polarization immunoassay for evaluating serum concentrations of tricyclic antidepressants (amitriptyline, imipramine, clomipramine, and doxepin) with respect to nonresponse, compliance, therapeutic window, and influences of age, sex, substance abuse, and toxicity. Abbott Laboratories TDx/TDxFLx Toxicology Tricyclic Assay FPIA (fluorescence polarization immunoassay) was used. This assay of 50 /uL samples contained tricyclic antidepressant antibodies raised in rabbits and fluorescein-labeled tricyclic antidepressant as a tracer. The assay was calibrated with imipramine in the range of 75 to 1000 fig/L (268 to 3571 nmol/L). Intra-assay and inter-assay coefficients of variation for internal quality control samples from the manufacturer were 4.2 and 4.7%, respectively. The limits of detection were 72,71,64, and 72 nmol/L for amitriptyline, imipramine, clomipramine, and doxepin, respectively. This high-throughput immunoassay was easy to use although amitriptyline, dosulepine, desipramine, and nortriptyline showed cross-reactivities ranging from 74 to 100%. 

The dynamic range of the standard curve for amitriptyline, nortriptyline, and imipramine was 25 to 250 /./g/mL it was 50 to 500 /ig/ml. for desipramine. Within-run and between-run coefficients of variation for the assay were below 10%. Up to 40 patient samples could be analyzed in 1 hr. 

Table 1.5 An example of standard deviation and coefficient of variation for different mean values...

Coefficient of variation for dust (dry assay) and dust (wet assay) was 8.5 and 8.7%, respectively. The range of trash contents is about 50 compared to about four for dust content. As explained by Montalvo (12). differences in dust content by the dry and wet assay methods are a result of a geometry effect associated with the former technique and the variation of adhesion force of dust on cotton with environment. Only one airborne dust measurement was taken on five of the six cottons. 

Method Validation. Reproducibility of the method was determined by analyzing one beer sample 10 times. Table 1 shows that the method provides very good reproducibility, with coefficients of variations for monitored aldehydes below 5.5%, except for (E)-2-nonenal. The higher coefficient of variation for (E)-2-nonenal may be due to extremely low levels of this aldehyde in the analyzed beer. 

Interpretation The higher coefficient of variation for (E)-2-nonenal may be due to extremely low levels of this aldehyde in the analyzed beer. 

That the spiked ethanol solution was exposed for different lengths of time at 50 °C (presumably) conveys a truth or fact that will not change thus, the statement is descriptive. However, the higher coefficient of variation for ( )-2-nonenal may not necessarily be due to the low levels of aldehydes in the analyzed beer hence,... 

Table I shows that the method provides very good reproducibility, with coefficients of variations for monitored aldehydes below 5.5%, except for (E)-2-nonenal. (From excerpt 4A)...

Equation (8) expresses the relation of the approximated variance of fraction X, as a function of the composition of the mixture and the square of the coefficient of variation. For example for a ternary mixture ... 

FIGURE 11.39 Results of intercomparison study of a mixture of organics found in ambient air. The concentrations (in ppbC) are shown as unfilled bare, along with the coefficient of variation ( ) for these measurements (adapted from Bernardo-Bricker et at., f995). 

The mean diameters of the large and small beads were 6.2 mm and 2.9 mm respectively with the coefficients of variation less than 2% within a batch. Mean masses of the batches of the larger beads ranged from 151.8 to 162.5 mg and the smaller beads had a mean mass of 19.9 mg. In no instance was the coefficient of variation for within batch variation greater than 3%. 

Results from the analyses showed there were no interferences from the other dyes present (Figure 3 and Table II). The coefficient of variation for the average analytical method recovery ( ) has been defined by the following equation... 

BARTLETT S TEST for homogeneity of CV s is applied in order to test the feasibility of "pooling the coefficients of variation" for any set of 18 generated samples (i.e., 6 at each of the 0.5, 1, and 2X OSHA standard levels). The following equation for the Chi-square, with 2 degrees of freedom, was used ... 

Relative error values for the elements ranged from zero to a high of 18% with most values being 5% or less. The 18% relative error was obtained for indium and is attributable to the low concentration of this element in the solution analyzed. Moreover, the indium values were obtained on the lower end of the working curve where the sensitivity is greatly reduced. Standard deviations and coefficients of variation for the elements of interest are at acceptable levels (less than 1% standard deviation and around 5% coefficient of variation) for this technique. Again it should be pointed out that the original purpose of the subject method was to develop a rapid routine analysis for the major and minor constituents in coal ash and related materials without the necessity of several preconcentration steps, solvent extraction techniques, or pH adjustments. 

RECOVERY AND REPRODUCIBILITY. Duplicates of 20 cm3 of pooled urine are subjected to the procedure on different days of the investigation. The coefficient of variation for the different steroids varied between 3.2 and 9.8% on different days, indicating satisfactory reproducibility. 

Because the inequalities among the various mean diameters are usually strengthened when the drop sizes are widely dispersed, the ratio of some higher-order moment to a lower-order moment is often useful as a measure of the dispersion of the drop sizes. For example, the coefficient of variation for the surface-weighted size distribution is a function of the ratio of the weight-weighted mean drop size to the volume-surface mean drop size. The variance of the drop-size distribution may also be expressed in terms of the moments of the unweighted size distribution. 

The coefficient of variation for data from a single instrument should be <5% and for data... 

Due to the high sensitivity of the IDA method quantification in the sub-ppb range, the Alternate Protocol can be applied without extensive sample cleanups. Due to the high similarity of labeled internal standard and analyte, the relative recovery of analytes from the matrix, whether oily or aqueous, approaches 100% (Guth and Grosch, 1993c Schieberle and Hofmann, 1998) most errors come from pipetting. The coefficient of variation for compounds present in ppb quantities is between 5% and 10%. 

Shim et al. [59] developed an HPLC method, with column switching, for the determination of omeprazole in plasma. The plasma samples were injected onto a Bondapak Phenyl/Corasil (37-50 ym) precolumn and polar plasma components were washed with 0.06 M borate buffer. After valve switching, the concentrated drug were eluted in the back-flush mode and separated on a /i-Bondapack Ci8 column with acetonitrile-phosphate buffer as the mobile phase. The method showed excellent precision, accuracy, and speed with detection limit of 0.01 /ig/ml. Total analysis time per sample was less than 20 min and the coefficients of variation for intra- and interassay were less than 5.63%. The method has been applied to plasma samples from rats after oral administration of omeprazole. 

Zarghi et al. [76] developed an HPLC method, using a monolithic column, for quantification of omeprazole in plasma. The method is specific and sensitive with a quantification limit of 10 ng/ml. Sample preparation involves simple, one-step extraction procedure, and analytical recovery was complete. The separation was carried out in reversed-phase conditions using a Chromolith Performance (RP-18e, 100 x 4.6 mm) column with an isocratic mobile phase consisting of 0.01 mol/1 disodium hydrogen phosphate buffer-acetonitrile (73 27) adjusted to pH 7.1. The wavelength was set at 302 nm. The calibration curve was linear over the concentration range 20-1500 ng/ml. The coefficients of variation for intra- and interday assay were found to be less than 7%. 

Fig. 8. Determination of coefficients of variation for protein microarrays. Replica spotting of Cy3 -labeled, biotinylated bovine serum albumin allows the intra- and interarray spot-to-spot reproducibility to be determined.

I Latex Preparation, In the present work it was found that the largest changes in particle size were obtained by variation of either the styrene concentration, the ratio of alcohol to water or by the choice of alcohol. In Tables I and II it can be seen that increases in either the styrene concentration or the ratio of ethanol to water caused the formation of latex particles of increased particle size. The coefficients of variation for the latices were always less than 10%. 

Higher conversions of xylan and glucan were seen with increases in both moisture content and inoculum size (Table 4), but no correlation was observed between the conversions and the relative amounts of inoculum and moisture (ratio of inoculum to moisture content not shown). Thus, it is unlikely that these two parameters comprise an interaction effect that is important to the operation of the system. Lower moisture contents gave lower overall amounts of degradation, but seemingly better selectivities for xylan degradation although coefficients of variation for conversions were... 

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