No	Item	Answer
Domain 1: Research Team and Reflexivity
Personal Characteristics
1.	Interviewer/facilitator	First author
2.	Credentials	MD, MSc
3.	Occupation	Senior advisor at an advisory council on public health and healthcare (public service) and PhD student.
4.	Gender	Female
5.	Experience and training	Economist and former general practitioner. PhD student. Courses on Atlas‐ti and qualitative research.
Relationship with participants
6.	Relationship established	The sampling of potential participants was initiated by interviewing a GP and CG, who were both acquaintances of the interviewer; the other participants were not.
7.	Participant knowledge of the interviewer	Former general practitioner. Interviews belonging to PhD research.
8.	Interviewer characteristics	She has a background as a GP and an affinity for geriatric care. Considering working with an interviewer who is trained as a GP may have encouraged the participants to speak frankly and directly from their own professional perspectives. The second coder has substantial experience in interview analysis but has no medical background, which helped us avoid a ‘medical’ bias in our data interpretation.
Domain 2: Study Design
Theoretical Framework
9.	Methodological orientation and Theory	Inductive thematic analysis
Participant Selection
10.	Sampling	A purposive and snowball method aiming to recruit professional pioneers.
11.	Method of approach	By email. Part of the recruitment of GPs took place at a broader meeting of GPs holding a specialization in geriatric care.
12.	Sample size	33 (18 clinical geriatricians and 15 general practitioners)
13.	Non‐participation	The response rates of clinical geriatricians and general practitioners were 86% and 54% respectively. Of the 21 CGs approached, one CG refused and two CGs did not respond to the first and reminder emails. A total of 28 GPs were approached. There were 6 non‐responders. 3 GPs responded positively, but did not respond to proposed dates. There were two drop‐outs (the interview was cancelled and there was no rescheduling (i.e. no response to proposed dates)). Two GPs of the same practice chose one participant. Their lack of time was the main reason not to participate.
Setting
14.	Setting of data collection	Five interviews were face‐to‐face, the others were held by telephone, as the medical practitioners’ busy schedules and varying locations required flexibility. The face‐to‐face interviews were held at the interviewee's office.
15.	Presence of non‐participants	No
16.	Description of sample	See Table 2. Basic characteristics of participants
Data Collection
17.	Interview guide	Main topics and subtopics are provided in table 1. A more detailed interview guide (in Dutch), including the introduction and closing of the interview, questions on the topics and questions on basic characteristics, is available upon request. In one case, the interview guide was sent to the interviewee in advance of the interview.
18.	Repeat interviews	No
19.	Audio/visual recording	Audio‐recording of all interviews
20.	Field notes	Yes
21.	Duration	Approximately 1 hour
22.	Data saturation	Yes
23.	Transcripts returned	3 interviewees wanted to receive the transcripts, which they did.
Domain 3: Analysis and Findings
Data analysis
24.	Number of data coders	2
25.	Description of the coding tree	Available upon request
26.	Derivation of themes	Derived from the data
27.	Software	Atlas‐ti 7.1.15
28.	Participant checking	Two participants provided feedback upon request.
Reporting
29.	Quotations presented	Yes
30.	Data and findings consistent	Yes
31.	Clarity of major themes	Yes
32.	Clarity of minor themes	Yes