Here's a list of reports to know some artifact trend data.
Average Age Report
The average age chart lets you know the average age of artifacts in one or more trackers you select.
Artifact Open/Close Chart (Multiple Trackers)
Use this chart to know the number of opened and closed artifacts over a period of time across one or more trackers or planning folders. This chart also helps in knowing the number of associated commits in specific repositories over a period of time. You can also know the total number of open artifacts through this chart.