Precision Of Test Methods Research Articles

Accounting for Precision Uncertainty of Toxicity Testing: Methods to Define Borderline Ranges and Implications for Hazard Assessment of Chemicals

For hazard classifications of chemicals, continuous data from animal‐ or nonanimal testing methods are often dichotomized into binary positive/negative outcomes by defining classification thresholds (CT). Experimental data are, however, subject to biological and technical variability. Each test method's precision is limited resulting in uncertainty of the positive/negative outcome if the experimental result is close to the CT. Borderline ranges (BR) around the CT were suggested, which represent ranges in which the study result is ambiguous, that is, positive or negative results are equally likely. The BR reflects a method's precision uncertainty. This article explores and compares different approaches to quantify the BR. Besides using the pooled standard deviation, we determine the BR by means of the median absolute deviation (MAD), with a sequential combination of both methods, and by using nonparametric bootstrapping. Furthermore, we quantify the BR for different hazardous effects, including nonanimal tests for skin corrosion, eye irritation, skin irritation, and skin sensitization as well as for an animal test on skin sensitization (the local lymph node assay, LLNA). Additionally, for one method (direct peptide reactivity assay) the BR was determined experimentally and compared to calculated BRs. Our results demonstrate that (i) the precision of the methods is determining the size of their BRs, (ii) there is no “perfect” method to derive a BR, alas, (iii) a consensus on BR is needed to account for the limited precision of testing methods.

A multi-method autonomous assessment of primary productivity and export efficiency in the springtime North Atlantic.

Fixation of organic carbon by phytoplankton is the foundation of nearly all open-ocean ecosystems and a critical part of the global carbon cycle. But quantification and validation of ocean primary productivity at large scale remains a major challenge, due to limited coverage of ship-based measurements and the difficulty of validating diverse measurement techniques. Accurate primary productivity measurements from autonomous platforms would be highly desirable, due to much greater potential coverage. In pursuit of this goal we estimate gross primary productivity over two months in the springtime North Atlantic from an autonomous Lagrangian float using diel cycles of particulate organic carbon derived from optical beam attenuation. We test method precision and accuracy by comparison against entirely independent estimates from a locally parameterized model based on chlorophyll a and light measurements from the same float. During nutrient replete conditions (80% of the study period), we obtain strong relative agreement between the independent methods across an order of magnitude of productivities (r2=0.97), with slight under-estimation by the diel cycles method (-19±5 %). At the end of the diatom bloom, this relative difference increases to -58 % for a six-day period, likely a response to SiO4 limitation, which is not included in the model. In addition, we estimate gross oxygen productivity from O2 diel cycles and find strong correlation with diel cycles-based gross primary productivity over the entire deployment, providing further qualitative support to both methods. Finally, simultaneous estimates of net community productivity, carbon export and particle size suggest that bloom growth is halted by a combination of reduced productivity due to SiO4 limitation and increased export efficiency due to rapid aggregation. After the diatom bloom, high chlorophyll a normalized productivity indicates that low net growth during this period is due to increased heterotrophic respiration and not nutrient limitation. These findings represent a significant advance in the accuracy and completeness of upper ocean carbon cycle measurements from an autonomous platform.

Flow cytometric determination of residual white blood cell levels in preserved samples from leukoreduced blood products

In preparation for a proposed consolidated testing service, Canadian Blood Services undertook the evaluation of a commercial test kit for the enumeration by flow cytometry of residual white blood cells (rWBCs) present in preserved samples recovered from leukoreduced (LR) blood and platelet products. The stability of preserved WBCs, the equivalency of WBCs used for spiking, test method precision, specificity, reliability, accuracy, and sensitivity were investigated. For comparative purposes, WBC counts were also determined by Nageotte as well as by flow cytometry. WBCs were stable up to 4 weeks at room temperature for all components by either method. Within methods, no differences were observed due to the source of WBC used for spiking purposes. By either method, test precision was acceptable (<20% coefficient of variation) and of similar reliability at a target value of 10 +/- 5 WBCs per microL. The flow cytometric method was shown to be more specific and accurate than the Nageotte method. Sensitivity by either method was 0.1 WBCs per microL. On average, Nageotte counts were lower than those observed by flow cytometry. These results demonstrate that WBCs in WBC stabilizing solution-treated samples from LR blood components were stabilized up to 4 weeks at room temperature and that rWBC determinations made with a WBC enumeration kit by flow cytometry have the required precision, specificity, reliability, and accuracy in the relevant test range. This validated WBC stabilization and flow cytometric counting method is considered acceptable as part of a quality control program for leukoreduced blood products.

Task Force Report on ASTM D 2419: Sand Equivalent Value of Soils and Fine Aggregate, Prepared for ASTM Subcommittee D 04.51

Abstract This interlaboratory study compared ASTM D 2419 test results using three different sample preparation techniques. Established preparation Procedures A and B were compared against a new proposed Procedure C, currently being used by the Georgia Department of Transportation (DOT). Sand equivalent (SE) testing was done at eight different laboratories, and the data were analyzed by ASTM Practice for Conducting an Interlaboratory Test Program to Determine the Precision of Test Methods (E 691) computer program, Interlaboratory Data Analysis Software. Results of this study conclude that the proposed Procedure C gives essentially the same results as Procedure A and is easier and less cumbersome to perform. Results also showed that there is no reason to differentiate between SE values above or below 80 when applying a precision statement. The second part of this study compared SE results from tests using minus No. 4 (4.75-mm) material against tests using minus No. 10 (2.0 mm). It was felt that SE testing with larger top-size particles, particularly with flat or elongated aggregates, tends to trap plastic fines and gives poorer results than tests run with smaller top-size particles. This study shows that tests using minus No. 10 (2.0-mm) material gives more consistent results than using minus No. 4 (4.75 mm).

Precision in polymer testing: An important world-wide issue

There is no question about the importance of testing in the modern technologically oriented world. We strongly rely on it. However, the quality of testing, especially on a laboratory-to-laboratory basis, is often marginal or poor. This poor test quality, or lack of agreement in test results, often upsets the commercial, scientific and regulatory efforts of society. Test method precision is a ‘figure of merit’ for various tests and the issue of obtaining valid precision parameters and clearly expressing the precision results is currently being addressed by standardization organizations such as ASTM and ISO. This paper gives an overview of the action on precision assessment currently being conducted in ASTM Committee D11 and ISO/TC-45, both of these being devoted to Rubber and Rubber Product testing. Definitions for precision, i.e. repeatability and reproducibility, are given in addition to details on the organization of interlaboratory programs needed to acquire the basic precision data. A precision example using the Mooney viscosity test is presented as well as a discussion of the uses of precision parameters and the problems currently being encountered in this work.

Parameters and Definitions in Harmonization of Collaborative Analytical Studies

Abstract IUPAC, AOAC, and ISO participate in developing, validating, and adopting analytical methods for international use. Harmonization of the different interests of these organizations is desirable, as is harmonization of parameters of precision of test methods. ISO Technical Committee 69 is responsible for standards that deal with statistical interpretation of test results and data, sampling procedures, and precision of test methods.

Precision of the Proposed Test Method to Measure Slag Hydraulic Properties

Abstract A method has been developed which tests the hydraulic properties of finely ground blast furnace slag. Results from round robin testing were analyzed according to the ASTM Practice for Conducting an Interlaboratory Test Program to Determine the Precision of Test Methods for Construction Materials (C 802). Evaluation of the data has confirmed the validity of the test method and appropriate precision statements have been developed.

The Role of Quality Assurance in Collaborative Testing

Collaborative testing is the traditional means used to establish the precision of test methods. The role that quality assurance plays in the collaborative testing of US Environmental Protection Agency stationary source test methods is presented. The applicability of the quality assurance procedures presented for routine use in compliance testing is also described.