you could also get in touch with @DiscourseMetrics.com and @Bas (about Community Analytics)
their tools can give you loads of extra stats so you don’t have to do the work … I’m looking at such tools at the moment myself
Up till now I’ve been doing this just in excel - you can export your user data and run a few queries to monitor this. I gave a value to each post read, to posts (replies) and to new threads, then categorised them accordingly
So far it shows 20% are ‘readers’, 25% are ‘participants’ and 15% are ‘creators’
I’ve found that most analysis tools are under-valuing the role of readers because of a focus just on the activity of posting. There is a big difference between inactive members and active readers!
Good luck!