Statistical artifacts: Critical approaches to the analysis of obsidian artifacts by portable X-ray fluorescence. (April 2019)

• Record Type: Journal Article
• Authors: Stroth, Luke; Otto, Raquel; Daniels, James T.; Braswell, Geoffrey E.
• Is Part Of: Journal of archaeological science. Volume 24(2019)
• Page Start: 738
• Page End: 747
• Publication Date: 2019-04
• Subjects: Archaeology -- Periodicals; Archaeology -- Research -- Periodicals; 930.1
• DOI: 10.1016/j.jasrep.2019.02.023
• Languages: English
• ISSNs: 2352-409X

Abstract

Abstract: In the past decade, chemical assay by portable X-ray fluorescence (pXRF) has become a common method of determining the geological origin of obsidian artifacts. We present source assignments made for 355 artifacts from the Late Postclassic site of Guadalupe, Honduras. Statistical studies of concentration data for six individual elements imply that obsidian from at least three sources (Güinope, La Esperanza, and Ixtepeque), and possibly two more (El Chayal and Otumba), was exploited in ancient times, but yield conflicting and ambiguous results for 5% of the collection. We argue that pXRF studies need to be conducted more critically and demonstrate how different statistical tools can yield contradictory source assignments for a significant portion of an obsidian collection. Visual sourcing supports discriminant function analysis over Mahalanobis distance assignments. Furthermore, element ratios imply that Otumba is not actually present. We are concerned that in obsidian studies, pXRF data are not consistently interpreted in ways that yield reproducible results. We propose an integrated methodology that employs pXRF, statistical analysis, visual sourcing, and—when needed and appropriate—destructive chemical assay to determine the source of "high-stake" artifacts.