¹www.csv.warwick.ac.uk/-bsrlu/dea/deal.htm is one of the most complete DEA pages on the Internet.

²These files are located in the Excel directory of the CD accompanying this book.

³This terminology comes from linear programming, where duality theory roughly establishes that for each primal model with n variables and m constraints, there exists a dual model with m variables and n constraints. The dual variables of the ratio model give the necessary information to create a virtual process for a relatively inefficient process. When the real process is relatively efficient, no virtual process can be more efficient than the real one; therefore, the dual values are equal to 0.