I am trying to establish any seasonality with what is, unfortunately, a large number of items and a relatively small time sample. I have 32,000 different items which have typically sold at a steady pace over the past three years. I have the sales of each item by month for the previous three years and am trying to identify those with larger sales over particular recurring monthly periods.
I am currently using a few ideas which pit single or small groups of consecutive months against the next year. Does any one have a better idea?