Abstract: Using international data for 18 vintages, we find systematic differences between the actual and stated alcohol content of wine. Our results suggest that rising alcohol content of wine may be a nuisance by-product of producer responses to evolving market and production environments.
See article here: Vinum Verum Viribus? Systematic Errors in Wine Alcohol Labels
ARE Update V. 19 no. 4, Mar/Apr 2016. Julian M. Alston, Kate B. Fuller, James T. Lapsley, George Soleas, and Kabir P. Tumber