Skip to main content
ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #367574
Research Project: Mitigating Alternate Bearing of Pecan - Bridge Project

Location: Fruit and Tree Nut Research

Title: Effects of quantitative ordinal scale design on the accuracy of estimates of mean disease severity

Author
item LIU, HUNG - Chung Hsing University
item TSAI, JIA - Fu-Jen University
item CHUNG, WEN - Chung Hsing University
item Bock, Clive
item CHIANG, KUO-SZU - Chung Hsing University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2019
Publication Date: 9/19/2019
Citation: Liu, H.I., Tsai, J.R., Chung, W.H., Bock, C.H., Chiang, K. 2019. Effects of quantitative ordinal scale Design on the accuracy of estimates of mean disease severity. Agronomy Journal. 9:595. https://doi.org/10.3390/agronomy9090565.
DOI: https://doi.org/10.3390/agronomy9090565

Interpretive Summary: The severity of plant diseases is needed for practical and research-related purposes including estimates of yield loss etc. Ordinal scales are used to categorize severity into ordered classes. The aim of this study was to compare mean estimates of severity based on various quantitative ordinal scale designs to nearest percent estimates, and explore whether the number of classes in an ordinal scale affect accuracy of that mean. A simulation method was employed. Results indicated scales with seven or more classes are preferable. Use of an amended 10% quantitative ordinal scale with additional grades at low severities resulted in a more accurate mean severity estimates compared to other scale designs. The results contribute to the development of plant disease assessment scales to improve accuracy of estimates of means disease severities.

Technical Abstract: Estimates of plant disease severity are crucial to various practical and research-related needs in agriculture. Ordinal scales are used for categorizing severity into ordered classes. Certain characteristics of quantitative ordinal scale design may affect the accuracy of the specimen estimates and, consequently, affect the accuracy of the resulting mean disease severity for the sample. The aim of this study was to compare mean estimates based on various quantitative ordinal scale designs to nearest percent estimates, and to investigate the effect of the number of classes in an ordinal scale on accuracy of that mean. A simulation method was employed. The criterion for comparison was the mean squared error of the mean disease severity for each of the different scale designs used. The results indicate that scales with seven or more classes are preferable when actual mean disease severities of 50% or less are involved. Moreover, use of an amended 10% quantitative ordinal scale with additional grades at low severities resulted in a more accurate mean severity compared to other scale designs. To further verify the simulation results, estimates of mean severity of pear scab on samples of leaves from orchards in Taiwan demonstrated similar results. These observations contribute to the development of plant disease assessment scales to improve accuracy of estimates of means disease severities.