Population survey (6)
I believe the answer is:
census
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">population survey</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for census that I've seen before include "People count" , "Periodic count as of population" , "Official count of population" , "Head-count" , "Official body count?" .)