There are two things that impact new item performance.
- You are not developing enough new items to replace dying items.
- The items you are developing do not perform as well as new items used to perform.
Go get your hands on some merchandising data. Count, by season, the number of new items offered, for the past five or six years. You'll quickly observe how much focus your merchandising team gave new items.
Next, analyze the performance of new items, by season. What do you see? Measure sales per item, and compare it across years ... if you are a cataloger, add thousand pages circulated (circ * square inches) to the analysis, if you're an email marketer, add a measure of how often new items were "featured" in each year.
You're going to quickly identify your problem when you run this report.