If you're looking for a way to quantify how active your authors have been, the Change Log report can help. 

You can get the following information:

• Who made changes to a tree.
• When the change was made.
• See changes for a single tree, or for all trees in your Organization.
• See all changes to all trees made for a specific author.
• Export reports to CSV format.

Try it yourself! 

• Go to Usage Reports. 
• Select Tree Reports.
• Select a Tree
• Under Tree Report, select Change Log.