Introduction
While longitudinal studies are valued for the insight they provide into how and why both individuals and groups develop and change over time, they also represent significant methodological challenges if studies are to produce valid results. The methods chosen by our own study of career choices and expectations amongst pharmacy students and pharmacy graduates were largely informed by the experiences of other longitudinal studies, such as Robinson and Marsland¹, and are presented here as a reflection on the problems we faced trying to engage a cohort distributed through fifteen GB Schools of Pharmacy.

Method
Many longitudinal research reports recommend paying close attention to recruitment strategies for engaging the subjects of the research.^1-3 In order to minimise refusal to participate we spent time ensuring that the study appeared interesting to the students we wanted to recruit. This resulted in the team identifying some pharmacy careers issues which we felt would be of interest to the cohort, such as the recruitment and retention problems in the profession.

More importantly, we realised that – if the study was to succeed – it was crucial to create some kind of rapport between the researchers and the subjects. In order to secure the engagement of participants we therefore needed to establish a relationship and a dialogue between the team and the cohort.⁴ To secure this, we first wrote to each Head of School of Pharmacy and asked them to nominate a member of staff to act as the point of contact in their school: a member of the team then worked with this person to arrange a visit to the School in which we could meet the students, tell them about the study, and ask them to complete a consent form for the study.

Results
Of the fifteen Schools of Pharmacy, thirteen have been visited by the team. There has been some variation in response rates achieved in each of the Schools. This variation in response rate may be attributed to the access given to the cohort – for example, whether members of the team met the students during a scheduled lecture slot or whether the meeting was outside timetabled hours. Furthermore, access to the cohort was not always through the nominated liaison member of staff in each School. Finally, some visits were delayed by different interpretations of the need for the study to be submitted to an institution’s ethical committee for review, and this may have affected the numbers present at the recruitment slot since undergraduate attendance tends to drop off over the course of a semester.

Discussion
Recruiting pharmacy students from all the GB Schools of Pharmacy has presented several challenges to our longitudinal study, and has so far achieved a range of response rates.

1. Robinson S, Marsden L. (1994) Approaches to the problem of respondent attrition in a longitudinal panel study of nurses’ careers. Journal of Advanced Nursing, 20: 729-741.
2. Goldstein H. (1979) The Design and Analysis of Longitudinal Studies. London: Academic Press
3. Plewis I. (1985) Analysing Change. John Wiley & Sons: Chichester
4. Aiken L.R. (1988) The problem of nonresponse in survey research. Journal of Experimental Education 56 (3): 116-119.