The Dublin III Regulation is a long-standing EU mechanism to determine Member States’ responsibilities for examining asylum claims.
Eurostat, the EU’s statistics agency, regularly publishes data on transfers under the Dublin Regulation which includes data on formal request refusals . The 2017 data publication is expected to be published shortly. The latest publication can be found here:
The Dublin III Regulation clearly sets out the acceptance criteria for requests and where these are not met the request will be refused.