Detecting referral and selection bias by the anonymous linkage of practice, hospital and clinic data using Secure and Private Record Linkage (SAPREL): case study from the evaluation of the Improved Access to Psychological Therapy (IAPT) service. - Simon de Lusignan; Rob Navarro; Tom Chan; Glenys Parry; Kim Dent-Brown; Tony Kendrick (BMC Medical Informatics Decis. Mak., 2011)