The ranking index will look at one product and one keyword as one unit. We then aim to summarize these units into one trend, whereby ranking developments on the first search result pages are factored more strongly into the trend than changes in pages further behind. When a unit moves from one page to another, the trend will also evolve more significantly.
If your ranking index has fallen strongly, it may be worth having a look at the detail pages of your products to determine where the the biggest ranking losses occured.
Cockpit > Monitored Products > Details
The most frequent tactic is the use of Sponsored Products (PPC) for the identified searchterms.