The possible pitfalls of using productivity data to evaluate variety performance

Lawes, R.A., and Fuelling, T.G. (2000) The possible pitfalls of using productivity data to evaluate variety performance. Proceedings of the Australian Society of Sugar Cane Technologists, 22. pp. 277-282.

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The variation and structure of block productivity data affect the interpretation of variety performance for both cane yield and CCS. The confounding factors inherent in block productivity data can bias any analysis and potentially lead to an over or underestimation of a variety's performance. Exploratory data analysis of Tully Sugar Ltd block productivity data determined the nature and variation of farm performance, variety distribution across farms, crop class distribution across farms, and the distribution of crop age between farms for 1997. All data were found to be unbalanced and unevenly distributed. The industry currently compares the means of CCS and cane yield for each variety grown in the district without considering confounding factors like age or crop class and ranks them accordingly. This method was compared to one derived from using a formal statistical procedure (referred to as a linear mixed model) that accounted for the effects of crop class, farm and time of harvest. When compared to the industry method of ranking varieties for cane yield, the linear mixed model improved the rank of Q138 by 2 places, and Q124 and Q149 by 1 place. The rank of Q117 declined by 2 positions, while Q120 and Q127 declined by 1 position. For CCS, the linear mixed model improved the rank of Q132 by 3 places, while the rank of Q124 declined by 3 places. To further demonstrate the significance of the bias and confounding effects inherent in block productivity data, the two methods were also used to evaluate the performance of Q152 and Q117 from 1994, when Q152 accounted for less than 1% of the cane supply, to 1997, when Q152 accounted for 18% of the cane supply. Q117 accounted for about 20% of the supply annually throughout this period. In 1994, the mean performance of Q152, determined using the industry method, suggested the variety had similar CCS and more yield than Q117. However, the linear mixed model method indicated that the yield was higher but the CCS was 0.42 units lower. By 1997, both methods showed that the yield of Q152 was higher than Q117 and the CCS was 0.95 units lower than Q117. Therefore, the mixed model was better able to characterise the performance of Q152 soon after its adoption by growers. This study highlights the value of using advanced statistical techniques to accommodate problems with productivity data and illustrates how these methods can be used to improve the prediction of a new variety's performance across a mill district.

Item ID: 13000
Item Type: Article (Research - C1)
ISSN: 0726-0822
Keywords: block productivity data; REML
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Date Deposited: 14 Dec 2010 04:39
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0799 Other Agricultural and Veterinary Sciences > 079999 Agricultural and Veterinary Sciences not elsewhere classified @ 100%
SEO Codes: 82 PLANT PRODUCTION AND PLANT PRIMARY PRODUCTS > 8203 Industrial Crops > 820304 Sugar @ 100%
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