This dataset covers 83% of the population of Wales and 80% of GP practices in Wales. It is linkable with anonymised fields for individuals and GPs to other datasets, including bespoke project specific cohorts. Each GP practice uses a clinical information system to maintain an electronic health record for each of their patients; capturing the signs, symptoms, test results, diagnoses, prescribed treatment, referrals for specialist treatment and social aspects relating to the patients home environment. The majority of the data is entered by the clinician during the patient consultation. Test results are electronically transferred from secondary care systems. There are no standard rules for recording data within primary care clinical information systems. Therefore, each individual clinician can record information in their own way. The majority use Read Code Terminology, however, sometimes this is applied behind the scenes by the clinical system and sometimes local codes are used. Read codes are not as precise as ICD 10 or OPCS codes. Coding standards have been agreed on for conditions monitored by the QOF (Quality Outcomes Framework) returns. Since the implementation of QOF these conditions have been coded in a more consistent way. Time coverage varies between each practice. A link to a list of the GP practices covered in this dataset can be found in Associated media