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Daniel Tholen Roderick Chappel Barbara Francis 《Accreditation and quality assurance》2006,11(8-9):400-407
International requirements for PT and EQA state that providers must demonstrate that samples are homogeneous and stable. However, testing for homogeneity and stability can be expensive, use samples that could otherwise serve as quality-control materials, and can also fail to detect significant inhomogeneity and instability. In some situations it may be preferable to use the results from participants to identify problems with sample lots, if historic results follow predictable distributions and a statistical decision rule can be produced. An unusually high proportion of incorrect results may indicate that samples were inhomogeneous or unstable. Conditions under which this can be demonstrated are discussed, and the efficacy of the proposal is demonstrated with two examples. This procedure is especially effective when there are a large number of participants and/or a historic small proportion of incorrect results. Providers who adopt this proposal will need to retain samples for testing and assume the risk of distributing bad samples.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia 相似文献
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Daniel William Tholen 《Accreditation and quality assurance》1998,3(9):362-366
There are three stages to evaluating a laboratory's results in an interlaboratory proficiency test: establishing the correct
result for the test item, determining an evaluation statistic for the particular result, and establishing an acceptable range.
There are a wide variety of procedures for accomplishing these three stages and a correspondingly wide variety of statistical
techniques in use. Currently in North America the largest number of laboratory proficiency test programs are in the clinical
laboratory field, followed by programs for environmental laboratories that test drinking water and waste water. Proficiency
testing in both of these fields is under the jurisdiction of the federal government and other regulatory and accreditation
agencies. Many of the statistical procedures are specified in the regulations, to assure comparability of different programs
and a fair evaluation of performance. In this article statistical procedures recommended in International Organization for
Standardization Guide 43, Part 1, are discussed and compared with current practices in North America.
Received: 22 April 1998 · Accepted: 12 May 1998 相似文献
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In a category with injective hulls and a cogenerator, the embeddings into injective hulls can never form a natural transformation,
unless all objects are injective. In particular, assigning to a field its algebraic closure, to a poset or Boolean algebra
its Mac-Neille completion, and to an R-module its injective envelope is not functorial, if one wants the respective embeddings to form a natural transformation.
Received January 21, 2000; accepted in final form August 10, 2001.
RID="h1"
RID="h2"
RID="h3"
ID="h1"The hospitality of York University is gratefully acknowledged by the first author.
ID="h2"Third author partially supported by the Grant Agency of the Czech Republic under Grant no. 201/99/0310, and the hospitality
of York University is also acknowledged.
ID="h3"Partial financial assistance by the Natural Sciences and Engineering Councel of Canada is acknowledged by the fourth
author. 相似文献
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Jiří Adámek Horst Herrlich Jiří Rosický Walter Tholen 《Applied Categorical Structures》2002,10(3):237-249
Weak factorization systems, important in homotopy theory, are related to injective objects in comma-categories. Our main result is that full functors and topological functors form a weak factorization system in the category of small categories, and that this is not cofibrantly generated. We also present a weak factorization system on the category of posets which is not cofibrantly generated. No such weak factorization systems were known until recently. This answers an open problem posed by M. Hovey. 相似文献
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We develop an elementary approach to the classical descent problems for modules and algebras, and their generalizations, based on the theory of monads. 相似文献
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Walter Tholen 《Mathematische Nachrichten》1983,114(1):63-85
In this paper factorization structures of an abstract category are considered, depending on a class ?? of morphisms which is not necessarily closed under composition; as soon as it is one obtains the usual factorization systems defined by the diagonal-fill-in property. General existence criteria for those factorization structures are proved, in particular for monotone-light factorizations which are defined for abstract categories and which are considered in more detail. Finally, sufficient conditions for a positive solution of the Orthogonal Subcategory Problem are derived from the existence of certain factorization structures. 相似文献