Drought occurs in tomato growing region. Cost of fertilizer increases 35%. Significant publicity is given to a study that describes the health benefits of eating tomatoes. Price of hamburgers decreases 70%. Economic expansion occurs (i.e. consumer incomes rise and tomatoes are a normal good). New technology improves tomato picking process. Diesel prices increase 80%. Cost of higher education rises 40%. A new tax on ketchup is established. Economic conditions in foreign countries improve dramatically