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Assessing the assessors: Quantifying observer variation in vegetation and habitat assessment



Vegetation assessment protocols used in research, monitoring and statutory planning often rely on the consistent application of methods by multiple assessors. Consequently, a study was undertaken to evaluate the application of a vegetation condition assessment protocol by a range of assessors. The aim of the study was to quantify variation among assessors in their measurement of field-based vegetation attributes using Queensland’s BioCondition protocol, and to determine the effect of variability on the final condition score. The study consisted of 77 assessors, ranging from nil to 25 years experience in vegetation assessment, who each undertook an assessment at one site following training. Six of the 20 attributes used to derive the final condition score were not assessed consistently, this being because of a small number of assessors who had misinterpreted the protocol and had inappropriately assessed some attributes. Despite inclusion of outliers, 82% of assessors were within 10 points of the median condition score for the site. Based on the results, the definition and measurement of problematic attributes have been either clarified or removed from the revised assessment procedure. The study demonstrated that with training prior to use, assessors were able to consistently assess condition at the study site.