Fig. 1
Diagram of exposeda person-time under five methods for studies of life-long conditions using electronic health record data. a individuals with an intellectual disability diagnosis prior to registration/transfer (i.e. prevalent users in pharmacoepidemiology studies) entered the cohort as normal. b Time 2 represents the date that the clinician was assumed to have input the first intellectual disability diagnosis on their GP electronic health record database, given by the system date (‘sysdate’) attached to the diagnosis and diagnosis date