Inter-indexer Consistency in Graphic Materials Indexing at the National Library of Wales

Purpose – This paper seeks to report a project to investigate the degree of inter-indexer consistency in the assignment of controlled vocabulary topical subject index terms to identical graphical images by different indexers at the National Library of Wales (NLW).Design/methodology/approach – An experimental quantitative methodology was devised to investigate inter-indexer consistency. Additionally, the project investigated the relationship, if any, between indexing exhaustivity and consistency, and the relationship, if any, between indexing consistency/exhaustivity and broad category of graphic format.Findings – Inter-indexer consistency in the assignment of topical subject index terms to graphic materials at the NLW was found to be generally low and highly variable. Inter-indexer consistency fell within the range 10.8 per cent to 48.0 per cent. Indexing exhaustivity varied substantially from indexer to indexer, with a mean assignment of 3.8 terms by each indexer to each image, falling within the range 2.5 to 4.7 terms. The broad category of graphic format, whether photographic or non-photographic, was found to have little influence on either inter-indexer consistency or indexing exhaustivity. Indexing exhaustivity and inter-indexer consistency exhibited a tendency toward a direct, positive relationship. The findings are necessarily limited as this is a small-scale study within a single institution.Originality/value – Previous consistency studies have almost exclusively investigated the indexing of print materials, with very little research published for non-print media. With the literature also rich in discussion of the added complexities of subjectively representing the intellectual content of visual media, this study attempts to enrich existing knowledge on indexing consistency for graphic materials and to address a noticeable gap in information theory