Methods
Sampling
The sampling frame was the UPBEAT-UK cohort study database of primary care patients with CHD. At the time of recruitment (December 2008 to January 2009) this numbered 376. Participants were drawn from GP, primary care CHD registers. Patients were recruited to the cohort study from four South London Boroughs (Lambeth, Lewisham, Southwark and Croydon) coterminous with Primary Care Trusts (PCTs) in South East and South West London, which all serve ethnically and socially diverse populations. Of the 376 participants in the cohort, 47 screened positive for depression using the PHQ2. Researchers from the main UPBEAT-UK study screened participants. At recruitment, participants were given the option of being interviewed in depth about their CHD and depression. 42 participants agreed. Of these, 5 were included in a pilot study to refine the interview topic guide. 1 of the remaining 37 declined to be interviewed and 3 could not be contacted or had died. Of the remaining 33, 30 were interviewed at which point interviewing was stopped as saturation had been reached.
Data Collection
One researcher (RS) conducted all the interviews, which were digitally recorded, transcribed verbatim and entered into NVivo8 qualitative software for analysis and data management. An interview topic guide was informed by the aims of the research, literature review, discussion with co-authors and findings from a preliminary, unstructured, interview study with depressed, cohort study participants. The topic guide covered perceptions of the relation between their physical and mental health, their experiences of living with depression, their opinions about interventions and their own self-management strategies. Patients were interviewed by the first author (RS) in a private space, either in their own homes or at their GP surgery.
Analysis
Interviews were analysed using a thematic approach involving a process of constant comparison between cases, identifying patterns and qualities in the texts. Texts were coded and re-coded iteratively until category saturation of each theme was achieved.
During the process of analysis, coding frames, themes and anomalous data were discussed regularly with a senior member of the research team (DR) and with members of the UPBEAT-UK research team, to corroborate findings.