Poll result incomplete in Civil Service (6)
I believe the answer is:
census
'poll' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for census that I've seen before include "Periodical population count" , "Official survey" , "Periodic count by statisticians" , "Official count of population" , "Population survey" .)