Population count (6)
I believe the answer is:
census
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">population count</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for census that I've seen before include "Periodical population count" , "Population survey" , "Periodic count by statisticians" , "Head-count" , "Official survey" .)