Take demand from the past year. After weighting by demand, create a frequency distribution of 1/3rd / 1/3rd / 1/3rd price points.
Then create a variable in your database ... low = bottom third of price points, average = middle third of price points, high = high third of price points.
Finally, sum annual demand for the past five years.
Look at the table here ... tell me what you observe. We'll discuss the table tomorrow.