Assessing the Accuracy, Intra-rater Repeatability, and Inter-rater Reliability of Disease Assessment Systems

Dollar spot of bentgrass, caused by Sclerotinia homoeocarpa, was chosen as a model pathosystem to evaluate the accuracy and precision of several disease assessment methods. Quadrats were assessed by visually estimating percent disease severity, by measuring percent reflectance of sunlight at 600 and 800 nm, and by image analysis of color photographic slides. Visual and reflectance assessments were performed by four raters and repeated 24-h later to obtain a measure of intra-rater repeatability. Linear regression of the original assessments (Y) versus the repeated assessments (X) revealed that intra-rater repeatability was highest for the 600-nm radiometric method as indicated by slope values not significantly different from 1.0 (P≤0.01) and intercepts close to and not significantly different from zero (P≤0.01) [...]