Hello, I need to setup multiple regression model for estimating trousers' prices based on their attributes. I have data for period 2001-2005 for 130 trousers. Not all of the trousers were available during this period. I also need to include GDP in the model for every observed year. I'm confused with this: e.g. trousers A were available in year 2001 and 2002 and trousers B in 2002 and 2003. I have columns in Excel designating all relevant attributes and GDP for certain year for every trousers. GDP was different for every year. How should I organize the best my data in Excel in order to perform regression? Should I first enter the data for for all available trousers models in 2001 with corresponding GDP (last column), and then data below for 2002 with corresponding GDP, etc.? I mean domething like this: Model | Year | Attribute1 | GDP AAAAA | 2001 | aaaaaaaa | 2,000,000 BBBBB | 2001 | bbbbbbbb | 2,000,000 AAAAA | 2002 | aaaaaaaa | 2,500,000 BBBBB | 2002 | bbbbbbbb | 2,500,000 Many thanks. John