Hello, I hope you are well. I am helping my girlfriend and her class group with their research paper, and a grammar question has come up. The full sentence, as I originally wrote it, is "Upon agreeing to participate, the students were asked for full compliancy and accuracy in recording their sleep and caffeine intake information." However, a group member said that "compliancy" is incorrect and it should be "compliance." Can you let me which form is correct? And if possible, why that is so? Thank you.
The correct word is compliance. Compliancy is listed in the dictionary as a synonym for one of the definitions of compliance (tendency to yield ot another's will, weak). I do not see compliancy used in practice very often.
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Compliancy is correct

No it's not. You have ruled regulations that you need to comply with. When you do, you're in compliance with them. Organisations don't have heads of compliancy but heads of compliance.
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