Technical issues

Determination of sample size

Instead of determining a specific number of patients a priori, patients were sampled to new focus groups until theoretical saturation appeared to be reached. Since we followed an iterative process of data collection and analysis, we felt that after the 4th focus group no new information – ideas, thoughts, and preferences – on the included categories was mentioned by patients. The 5th focus group was basically conducted to confirm previous findings. Throughout our iterative process of data collection and analysis we continuously evaluated in how far the purpose of our focus groups (see research objectives in publication) was reached and whether additional focus groups might provide further relevant information.

Adequate understanding and framing of attributes

Within the iterative process of data collection and analysis patients provided much of the wording and framing of attributes/levels as well as giving examples for them. For the attribute “treatment effectiveness”, which we had ideas on from our literature search and the expert interviews, we left it entirely up to the patients to define what was considered their primary treatment goal. Regarding the other attributes, we adapted the interview guide and added e.g. graphs if concepts seemed to be difficult to understand. Whenever necessary, the researchers’ preliminary wording and framing of potential attributes was adapted to the patients’ words and examples on these attributes. Especially the first step of the discussion of attributes (see interview guide) during the first two focus groups led to adaptations. The table below provides some examples of the development towards patient based wording and framing. After the focus groups were finished and AHP/DCE questionnaires were developed, we also pilot-tested the questionnaire in a few patients. The results of these pilot tests, however, are not within the scope of the present paper.

Examples of development of wording/framing throughout focus groups
Attributes / Researchers’ preliminary
ideas on wording / framing / Insights from focus group interviews
Effectiveness / See scenarios in interview guide / Confirmation of anticipated scenario, immediate responses by patients (scenario 2)
examples of what improvement of visual function means to patients (e.g. “see without magnifier”, “drive a car”)
Approval / Approval / Patients confused approval with reimbursement and doctor’s license. Group discussion after use of improved verbal and graphical explanation revealed that patients were better able to understand the concept and differentiate it from the other aspects like reimbursement
Monitoring / Optical Coherence Tomography,
Visual acuity test (ETDRS) / Described by patients as “Photo of the eye” & “eye test”
Side effects / Identification of examples during expert interviews/ literature search / Selection of typical examples for mild side effects that were mentioned by patients and severe ones they were most aware of.
Injection frequency / Range of injection intervals between 1-6 months were considered / Patients preferred to have less injections, but considered the larger injection intervals unrealistic, levels were refined accordingly.
Also, after the first two focus groups, patients were informed that injection frequency should not be confused with effectiveness.