Averages to include blank rows

Perfect, I just solved this by creating two measures, one for distinct count of week and other toal encounters and also tried your way. The results for both the method are same. However, your method is easy and quick. 

The next issue I have is few employees started in the middle of the year, say June. Both the methods mentioned above is calculating all the weeks since Jan. 

How do I set a conditional saying if any week has an input (basically means new employee joined), then start doing rolling average from that point forward. 

I am also anticipating another issue where an employee left, so provide a condition for a stop for particular employees.