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United States Department of Agriculture

Agricultural Research Service

Title: An investigation on the sampling bias of the beard method as used in high volume instrument

Authors
item Cai, Yiyun - LOUISIANA STATE UNIV
item CUI, XIAOLIANG
item RODGERS, JAMES
item Martin, Vikki - COTTON INCORPORATED
item Watson, Mike - COTTON INCORPORATED

Submitted to: Journal of Textile Institute
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 7, 2009
Publication Date: November 1, 2010
Citation: Cai, Y., Cui, X., Rodgers III, J.E., Martin, V., Watson, M. 2010. An investigation on the sampling bias of the beard method as used in high volume instrument. Journal of Textile Institute. 101:(11):958-966.

Interpretive Summary: The beard sampling method is used by the High Volume Instrument (HVI) system to generate fibrograms for measuring cotton fiber length parameters. HVI is extensively used because of its speed and accuracy. A fundamental issue about the beard sampling method is its bias. In other words, is the length distribution of the sampled specimen fibers the same as the distribution of the original fibers? Even though different assumptions regarding the bias have been proposed, we have seen discrepancies in measurements that cannot be explained by using these assumptions, especially in the short fiber region. Short fibers in cotton samples have important impacts on cotton processing efficiency and product quality. It is important to investigate the bias of the beard sampling method. In this paper we report a fundamental research, including experimental and theoretical analysis, and three-dimensional computer modeling. The results reveal the bias by the beard sampling method and help us better understand how this sampling method affects the length distribution of sampled cotton fibers. We also report the influence of the sampling method on Short Fiber Content (SFC) caused by the bias.

Technical Abstract: The beard method is used for sampling cotton fibers to generate fibrograms from which length parameters can be obtained. It is the sampling method used by the High Volume Instrument (HVI). HVI uses a fiber comb to sample cotton fibers and form a fiber beard for measuring fiber length parameters. A fundamental issue about this sampling method is its bias. There have been different assumptions regarding the bias of the beard sampling method. The original fibrogram theory for the beard method adopted an assumption that this procedure is length-biased, while other researchers later revised this assumption to that each fiber has equal probability of being sampled regardless of its length (unbiased assumption). In our experiments, we have seen discrepancies in measurements that cannot be explained by using length-biased or unbiased assumptions, especially in the short fiber region. Therefore, it is important to investigate the bias of the beard method. We report a fundamental research, including experimental and theoretical analysis, and three-dimensional computer modeling, that reveals the bias due to this sampling method. We found that the beard sampling method as used in HVI is not completely length-biased; it is similar to the original sample except in the short fiber region. Short Fiber Content (SFC) of the sampled fiber is lower than that of the original fiber, and this difference is inherently introduced by the sampling method.

Last Modified: 8/19/2014
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