Components of immigration quota (5)

I believe the answer is:

ratio

'quota' is the definition.
(thesaurus)

'components of immigration' is the wordplay.
'components of' indicates the answer is hidden within the clue (I've seen 'component of' mean this (I've seen this in other clues)).
'RATIO' can be found hidden inside 'immigration'.

(Other definitions for ratio that I've seen before include "Comparative figure" , "Comparative measure" , "Mathematical relationship" , "nine-to-five, say" , "Measure of two relative sizes" .)

I've seen this clue in The Guardian.

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