Submitted to: Geocarto International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2012
Publication Date: 1/22/2013
Publication URL: http://handle.nal.usda.gov/10113/58782
Citation: Gearhart, A.L., Booth, D.T., Sedivec, K.K., Schauer, C.S. 2013. Use of Kendall's coefficient of concordance to assess agreement among observers of very high resolution imagery. Geocarto International. 28(6):517-526. Interpretive Summary: Differences among observers of high resolution imagery are well documented. However use of traditional statistical measures to detect these differences such as analysis of variance (ANOVA) and chi-squared are cumbersome with large sample sizes and more than two observers. We used a novel statistic called Kendall’s Coefficient of Concordance or Kendall’s W which has been used in social sciences for assessing agreement among observers, but not in imagery analysis. We found that Kendall’s W detected differences among six observers of very high resolution imagery. This statistic can be used to ascertain that observers of imagery are in agreement.
Technical Abstract: Ground-based vegetation monitoring methods are expensive, time-consuming, and limited in sample-size. Aerial imagery is appealing to managers because of the reduced time and expense and the increase in sample size. One challenge of aerial imagery is detecting differences among observers of the same imagery. Six observers analysed a set of 1-mm ground sample distance (GSD) aerial imagery for graminoid species composition and important ground cover characteristics. Kendall’s coefficient of concordance (W) was used to measure agreement among observers. The group of six observers was concordant when assessed as a group. When each of the observers was assessed independently against the other five, lack of agreement was found for those graminoid species that were difficult to identify in the aerial images.