Reliability and accuracy of visual methods to quantify severity of foliar bacterial spot symptoms on peach and nectarine

Abstract

The objectives of this study were to assess the reliability and accuracy of visual methods used to quantify the severity of bacterial spot (Xanthomonas arboricola pv. pruni) symptoms and evaluate the effects of rater experience on the quality of disease estimates. Three cohorts of raters differing in experience with disease assessment rated three sets of peach or nectarine leaves (n ‡ 103; disease severity levels from 0% to 100%) by direct estimation of percentage leaf area with symptoms. Four of the experienced raters also rated the leaves using a 1-7 interval scale. Actual disease severity on the leaves was obtained with the APS ASSESS image analysis software. Equivalence tests based on a bootstrap analysis were used to compare the rating scale and direct estimation methods, and to evaluate the effects of rater experience, computer training and human instruction on accuracy and reliability of disease estimates. In concordance analysis of continuous variables, with data from scale converted to percentage, the direct estimation method resulted in more accurate and reliable estimates than the interval scale. Analysing the scale data without conversion to percentage improved the concordance statistics for the scale but not sufficiently to match the direct estimation method. Accuracy was affected more by rater experience and intrinsic ability than reliability. Instruction on disease symptoms resulted in the largest improvement in estimates from inexperienced raters. Accurate and reliable direct estimation of bacterial spot severity on peach and nectarine can be made by raters with varying levels of experience provided they receive sufficient instruction.

The Effect of Horsfall-Barratt Category Size on the Accuracy and Reliability of Estimates of Pecan Scab Severity

“…actual scab sevedty explored in this study, and often gave an inferior estimate of severity compared with NPEs. This observation is supported by previous studies (1,9,11,22). Although results based on the full range of the H-B scale had previously been reported (5), the differences between assessment methods and rater experience found herein over different actual disease severity ranges indicate where the H-B scale is least often accurate and reliable (25* to 75% severity).…”

“…Eirst, the NPEs were compared with the H-B scale in each severity range 0 to 6, 6+ to 25, and 25+ to 75% for expedenced and inexpedenced raters in each image cohort. This was done by calculating the difference between the means for assessment method (NPE -H-B) and performing an equivalence test (1,34,35) using bootstrapping to calculate 95% confidence intervals (CIs) for the difference between the means. In equivalence testing, equivalence (i.e., no difference between methods or groups) is the alternative hypothesis (Hi) and the null hypothesis (Ho) is noncquivalence (i.e., a difference between methods or groups) (12).…”

“…various dedvatives (1,11,18,21,30), which are interval scales that partition the percent severity scale into categories based on percent area diseased. The H-B scale is divided into 12 logarithmically increasing, then decreasing, categories symmetdcal around 50%.…”

Validação de escala diagramática para quantificação da severidade da antracnose do colmo do milho

“…Mesmo com a utilização da análise de regressão, o uso do ρ c e o teste de equivalência (95% IC) foram importantes para interpretação das avaliações realizadas pelos dez avaliadores. O coeficiente de Lin (ρ c ) tem sido usado com muito sucesso em vários trabalhos (BOCK et al, 2010;CAPUCHO et al, 2011;YADAV et al, 2012;RIOS et al, 2013), e mais recentemente o teste de equivalência também, facilitando ainda mais a conclusão dos resultados (BARDSLEY & NGUGI, 2012;YADAV et al, 2012;RIOS et al, 2013).…”

“…Para todas essas variáveis obtidas pela análise de correlação concordante de Lin, incluindo a reprodutibilidade, a diferença entre a média foi calculada (com escala -sem escala e escala proposta -primeira escala) e um teste seguinte foi usado para analisar sua significância (Tabela 1) (YI et al, 2008;BARDSLEY & NGUGI, 2012;YADAV et al, 2012; Tabela 1 -Efeito da escala proposta na acurácia e precisão, por meio da avaliação da antracnose do colmo em 139 entrenós por 10 avaliadores. …”