Testing for Homogeneity

Homogeneity. Visual tests for homogeneity are generally used to judge uniformity. 

A useful source of details such as likely impurities, stability and tests for homogeneity of amino acids is Specifications and Criteria for Biochemical Compounds, 3rd edn. National Academy of Sciences, USA, 1972. 

Materials are chosen such that they are, as far as possible, representative of the type of material that is normally analysed. This will be in terms of the matrix and the concentration range of the analyte. Materials must be tested for homogeneity... 

Direct participation of the oceanographic research community will enable collection of matrix-based materials such as natural seawater or sediments in an efficient manner (for example, material collection could be combined with other scheduled research activities). Furthermore, the extensive analytical skills of the oceanographic research community can be harnessed to conduct the necessary testing for homogeneity, stability, and ultimately characterization of the proposed reference materials. At the same time, complete success requires the participation of reference material producers, who bring to the table extensive knowledge and experience in the preparation and stabilization of reference materials, and on occasion access to necessary facilities. 

Snedecor GW, Cochran WG (1967) Variance test for homogeneity of binormal distribution. Statistical methods, 6th edn. Iowa State University Press, Ames, pp 240-241... 

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 ... 

If a sample has been analyzed by k laboratories n times each, the sample variances of the n results from each laboratory can be tested for homogeneity —that is, any variance outliers among the laboratories can be detected. The ISO-recommended test is the Cochran test. The statistic that is tested is... 

Spreadsheet 2.3. Cochran test for homogeneity of variances in the soil analysis example given in the text. 

The above analysis assumes that the results are normally distributed and without outliers. A Cochran test for homogeneity of variance and Grubbs s tests for single and paired outliers is recommended (see chapter 2). Data from... 

C test standard statistical test for homogeneity of variance. 

In order to test the feasibility of pooling the coefficients of variation, Bartlett s test for homogeneity of CV s was applied. The CV jp may be pooled at the 1% significance level for "n" sets of data, if x 2.91, where... 

Bartlett s test for homogeneity of variances at 0.5, 1 and 1.5 times the OSHA standard showed that the variances may be pooled. Therefore, the coefficient of variation was calculated from the pooled variances ... 

This term might be used to describe a metal alloy sample known to be inherently stable, tested for homogeneity as part of routine production quality control and analysed by both the laboratory s routine method (say, XRF) and an alternative method (say, dissolution and measurement of the solution by ICP-OES). 

BARTLETT-test for homogeneity of variances (99%J Critical value 11.300 ... 

In terms of the statistical methods of the partial life cycle whole-effluent tests, survival, growth, and reproduction data from the 7 day cladoceran or fish exposure are often analyzed using hypothesis testing to determine acceptable concentrations. In order to determine the appropriateness of using parametric statistical methods, the data are first tested for normality of distribution and homogeneity of variance, for which the US EPA recommends the use of Shapiro-Wilk s test and Bartlett s test, respectively. Kolmogorov test for normality and Levine s test for homogeneity can be also used for these purposes. Dunnett s anova test is typically used for a... 

Samples must be homogeneous and tested for homogeneity, and should be coded at random, including the two or more blind replicates. A blank or negative control, and, if available, reference materials should be provided. Spiked materials are recommended for recovery study, incurred materials for residues study. 

In-process testing is an essential part of the manufacturing process for parenteral pharmaceuticals. It is a quick way to confirm that the concentration of the active ingredient in the bulk solution is accurate and within specification limits. It is also used to test for homogeneity of the bulk solution by testing samples from top, middle, and bottom portions of the tank. 

Unless the product is being tested for homogeneity, composites may be assayed, rather than individual units. If more than one container is sampled at a given sampling time, an equal number of units from each container may be combined into the composite. If composites are used,... 

A technique which has not yet been applied to polysaccharides is ultra-centrifugation with a density gradient in the cell. In this method, the molecules sediment until they come to equilibrium with solvent of their own density, and concentration bands are set up corresponding to the different polymeric species. This technique may provide a sensitive test for homogeneity. 

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