study examining transition from child to adult healthcare services, with young people with cerebral palsy (CP) as one exemplar group. This longitudinal study offered the opportunity to evaluate potential differences in recruitment of young people with CP using two population-based UK registers for which participation in previous research was known, the North of England Collaborative CP Survey (NECCPS)[@R15] and the Northern Ireland CP Register (NICPR).[@R16] Equally, differences in the operating procedures of the two registers allowed assessment of the effect of Direct (through the researcher from the register) and Indirect (through a clinician known to the family) contacts with families on their decision to take part in research.

The goal of this study was to investigate whether being contacted about or participating in previous research and method of approachingyoung people approached about joining the transition study.

Not-approached: young people who could not be traced or the research team was advised not to approach.

Responders: those approached who responded; they either then declined to take part or were recruited into the transition study.

Non-responders: those approached who did not respond to the initial or follow-up letters.

Recruited: those approached who responded and consented to take part in the transition study.

Refusers: a combined group which included non-responders (passive refusal) and responders who declined to take part in the transition study (active refusal).

Direct approach: when young people and their families were contacted through the researcher from the register.

Indirect approach: when young people and their families were contacted through a clinician known to the family.

Young people were eligible for inclusion in the transition study