An official count has statisticians in agreement (9)
I believe the answer is:
consensus
'agreement' is the definition.
(I know that consensus is a type of agreement)
'an official count has statisticians' is the wordplay.
'an official count' becomes 'census' (I've seen this before).
'has' is an insertion indicator.
'statisticians' becomes 'ons' (I can't justify this - if you can you should believe this answer much more).
'census' placed around 'ons' is 'CONSENSUS'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for consensus that I've seen before include "Unanimity" , "General agreement" , "agreed" , "Majority view" , "General opinion" .)