ISIS can 'muster' between 20,000 and 31,500 fighters, CIA says

Quote:

A CIA assessment puts the number of ISIS fighters at possibly more than three times the previous estimates.

The terror group that calls itself the Islamic State "can muster between 20,000 and 31,500 fighters across Iraq and Syria," a CIA spokesman told CNN on Thursday.

Analysts and U.S. officials initially estimated there were as many as 10,000 fighters, including those who were freed from prisons by ISIS, and Sunni loyalists who have joined the fight as the group advanced across Iraq.
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How do we get this estimate?
This is the number of people that are taking orders from ISIS leadership - which I think is the current definition of ISIS/ISIL/IS/Daesh from the AO? I have seen no information on methodology.


ISIS can 'muster' between 20,000 and 31,500 fighters, CIA says