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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #307435
Title: The effects of rater bias on hypothesis testing when using different assessment methods to estimate disease severity

Author
item CHIANG, KUO-SZU - National Chung-Hsing University
item Bock, Clive
item EL JARROUDI, MOUSSA - University Of Liege
item DELFOSSE, PHILLIPPE - Centre De Recherche Sur Les Macromolécules Végétales (CERMAV)
item LI, YI-HSUAN - National Chung-Hsing University
item LIU, HUNG-I - National Chung-Hsing University

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 3/9/2014
Publication Date: 11/1/2018
Citation: Chiang, K., Bock, C.H., El Jarroudi, M., Delfosse, P., Li, Y., Liu, H. 2018. The effects of rater bias on hypothesis testing when using different assessment methods to estimate disease severity [abstract]. Phytopathology. 104:S3.26.

Interpretive Summary:

Technical Abstract: Bias (over and underestimates) in estimates of disease severity, and the impact of that inaccuracy on hypothesis testing using different disease scales were explored. Nearest percent estimates (NPE), the Horsfall-Barratt (H-B) scale and four different linear category scales (5% and 10% increments, with and without additional grades at low severity) were compared. Actual values (by image analysis) and estimates by 4 different raters of the severity (0 to 100%) of Septoria leaf blotch on leaves of winter wheat were used to develop distributions for a simulation model. The simulations were based on i) all the 4 raters data combined, ii) only the most accurate rater estimates, and iii) only the most biased rater. Regardless of the effect of rater ability, we found that, there were lower type II error rates with NPEs as compared with the other category scales at severities of 80 to 100%. On the other hand, with lower severities (0 to 20%), the 5% and 10% scales with additional grades had type II error rates comparable to those for the NPEs. Raters who overestimated severity and used the H-B scale had the highest risk of a type II error when the mean disease severity was low (=10%). Knowledge of how rater ability and scale type can affect hypothesis testing can be used to improve disease assessment as well as to provide a logical framework for developing standard area diagrams.