Alternate States with Date Range

[#1]

I have a requirement to show program participation data with alternate states, so the user can select one set of years/months to compare to another set of years/months to see metrics such as count of participants.  In the program participation data, i have a participation start/stop date for each participant.  I'm seeking advice on how to write my expression so that it will count participants when the selected year/month for each alternate state falls within their start/stop dates. 

I started with an interval match to get a list of all actual dates between each participant's start/stop dates but I finally killed the reload when it reached over 1.5 billion rows - that did not seem efficient.

I've attached a sample file that hopefully makes clear what i'm trying to do.

Thanks!!

[Gysbert_Wassenaar · Accepted solution]

Maybe like in the attached example.

[#3]

YES!  This works perfectly... as long as the years/months chosen are successive (as opposed to selecting just Feb & March of 2012 and 2013 for example) but for my purposes that is how the users should be selecting anyway.  Thanks so much!!