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Thromb Haemost 1985; 54(03): 704-708
DOI: 10.1055/s-0038-1660102
Original Article
Schattauer GmbH Stuttgart

Prothrombin Time Proficiency Testing: A Robust Grading Method

Yangsook Han
The Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany, New York, USA
,
William B Lawson
The Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany, New York, USA
,
W Jean Dodds
The Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany, New York, USA
,
Charles E Lawrence
The Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany, New York, USA
› Author Affiliations
Further Information

Publication History

Received 28 May 1985

Accepted 27 August 1985

Publication Date:
19 July 2018 (online)

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Summary

A robust two-way analysis of variance technique was applied to determine simultaneously the effects of method and thromboplastin on prothrombin time. A new approach to outlier detection for two-way analysis of variance was used. Focusing on the underlying error structure improved the uniformity of the grading procedure in the hematology proficiency testing program of the New York State Department of Health.

The logarithm-transformed scale produced constancy of error variance and resulted in uniformity of the acceptable spread of data. The common variance was lower than that obtained by previous methods and allowed for a narrower acceptable range of reported prothrombin times by reducing the inflated standard deviation, thus improving the efficiency of the grading procedure.

For proficiency testing, no advantage was found in the use of either a common thromboplastin or freeze-dried, coumadinized patient plasmas rather than artificially depleted commercial plasmas, except for special purposes.

Keywords

Proficiency testing - Robust estimation - Outliers - Prothrombin time - Instrumentation - thromboplastin variables
 

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