Keynote address, International Symposium on Forecasting, June 2009. Abstract Extremely bad data, extremely poor methods and extremely difficult problems will be used as the basis of some extremely useful lessons. I will describe three cases from my consulting experience and draw some general lessons that are widely applicable. The first case involved forecasting passenger traffic on an Australian airline. The data showed variations due to school holidays, major sporting events, competitor activity, industrial disputes, changes in fare structures, and other …