Estimating the Fraction of 'Questionable' Artwork by Henry Moore for Sale on Ebay : Application of Latent Class Screening Test Methodology

While the internet has provided consumers with new ways to purchase goods, it also has allowed less scrupulous businesses and individuals to offer poor quality or mislabeled items. In particular, the operators of internet auction sites may not guarantee the quality or genuineness of the items listed. A latent class approach originally developed to estimate the accuracy of medical tests and the prevalence of an infection is adapted to provide estimates of the prevalence of “questionable” art work offered on eBay. The method requires the existence of two subpopulations with a different prevalence of the trait and each subject is classified by two different tests. As Henry Moore produced less expensive lithographs and etchings, in addition to small sculptures and original drawings, two subpopulations of artwork were available. After discussing the issue of “fakes” with experts on Henry Moore, a Bayesian approach was adopted. The results showed that about 90% of the drawings and small sculptures listed on eBay are “questionable” while most, about 90 to 95% of signed prints are genuine. Because the methodology does not require a “gold standard” it can be adopted by consumer protection agencies or producers of expensive items to monitor the authenticity of items offered to the public on internet auction sites