Committee on microbiological and extraneous materials.
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Animals↗
Biomedical subjects
Foster D McClure
Publications and source records attributed to Foster D McClure.
Validity of the percent reduction in standard deviation outlier test for screening laboratory means from a collaborative study.
AOAC INTERNATIONAL recommends an outlier test that is based on the "percent reduction in standard deviation" (PRSD) for screening the highest or lowest and 2-highest or 2-lowest laboratory means from a collaborative study. The original critical values that were developed to assess the significance of the test statistics associated with the PRSD test were obtained by simulation. In this paper, we answer several questions relative to the validity of the simulated critical values and develop formulas, based on the Student's t-distribution, to compare the simulated and formula-based critical values. Assumptions and derivations of formulas are provided along with selected tabular critical values that are used to test hypotheses at various levels of significance.
Food Analysis↗
Computation of HORRAT values.
The formula for the Horwitz ratio (HORRAT) as presented in the Study Director's Manual of AOAC INTERNATIONAL is applicable only when the concentration is in the unit/unit form (e.g., microg/microg, g/g, etc.). When the analyte concentration is a trace or mass fraction amount (e.g., microg/g), the formula generates incorrect HORRAT values. Alternative calculation procedures are presented to circumvent such problems.
Food Analysis↗
Determination of sample size for validation of allergen-screening methods.
For various levels of confidence (i.e., 80 and 90%) and ratios (K = sigmap2/sigmaN2, where sigmap2 and sigmaN2 are the analyte variances for the positive and negative distributions, respectively), sample sizes sufficient to test the requirements that a given method detects > or = 90% of the positives (> or = 5 ppm of a given analyte) while misclassifying < or = 10% of the negatives (implying a specificity rate, true negatives that will be correctly classified, of 90%) were estimated by using a rationale that minimizes the cost of sampling.
Allergens↗
Committee on Microbiology and Extraneous Materials.
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Botulinum Toxins↗
Sample sizes needed for specified margins of relative error in the estimates of the repeatability and reproducibility standard deviations.
Sample size formulas are developed to estimate the repeatability and reproducibility standard deviations (Sr and S(R)) such that the actual error in (Sr and S(R)) relative to their respective true values, sigmar and sigmaR, are at predefined levels. The statistical consequences associated with AOAC INTERNATIONAL required sample size to validate an analytical method are discussed. In addition, formulas to estimate the uncertainties of (Sr and S(R)) were derived and are provided as supporting documentation. Formula for the Number of Replicates Required for a Specified Margin of Relative Error in the Estimate of the Repeatability Standard Deviation.
Chemistry Techniques, Analytical↗
Determining a one-tailed upper limit for future sample relative reproducibility standard deviations.
A formula was developed to determine a one-tailed 100p% upper limit for future sample percent relative reproducibility standard deviations (RSD(R),%= 100s(R)/y), where S(R) is the sample reproducibility standard deviation, which is the square root of a linear combination of the sample repeatability variance (s(r)2) plus the sample laboratory-to-laboratory variance (s(L)2), i.e., S(R) = s(L)2, and y is the sample mean. The future RSD(R),% is expected to arise from a population of potential RSD(R),% values whose true mean is zeta(R),% = 100sigmaR, where sigmaR and mu are the population reproducibility standard deviation and mean, respectively.
Calibration↗
On determining a 1-tailed upper limit for future sample HorRat values.
Two formulas were developed for use in computing 1-tailed upper limits for future HorRat values obtained from the collaborative study of materials. One formula is applicable when a future sample HorRat value H [formula: see text] is computed based on a known concentration (e.g., C = spike level and RSD(R) is the sample relative reproducibility standard deviation) and the other formula is applicable when the true concentration (C) is unknown and a future sample HorRat value [formula: see text] is computed using the sample mean (e.g., y, the collaborative study overall mean for an analyte). A Monte Carlo simulation procedure was developed using the Statistical Analysis System (SAS) software to assess the accuracy of the 2 developed formulas. Based on the degree of closeness between the simulated and calculated limits, the formulas for computing upper limits for future sample HorRat values will prove to be useful to Study Directors in determining worst case scenarios concerning a method's reproducibility precision relative to that predicted using the "Horwitz equation". We also define the current empirical HorRat limits as 1-tailed 100p% upper limits to assess the statistical consequence, in a probability sense, of their application as an analytical methods screening tool.
Algorithms↗