by J. Nielsen and R. Mack, John Wiley and Sons, Inc., 1994 Use a team of evaluators One evaluator => between 20% and 51% of the problems Two evaluators => can identify over 50 % of the problems Three evaluators => can identify over 60 % of the problems The curve flattens after five evaluators; it would take more then 15 evaluators to identify 90% of the usability problems The evaluators should do their evaluations independently of each other and only compare results after each of them has looked at the design and written his/her evaluation report