What is the average percentage of domain names sold?

I am wondering if it is tracked someplace possibly or if it's already discussed but was wondering What is the annual percentage of domains sold vs domain portfolio on average? Say minimum of 100 domains owned.
So if you own 1,000 domains how many of those sell in one year? I am hearing 1% to 2% does that sound accurate?

 

Probably less than 1% for mere mortals.