Table 3 Outcomes, measurement instruments and timing

Level of engagement with ACP

ACP Engagement Survey 15-item version [24]

• Reported on an overall average 5-point Likert scale (range 1–5)

Patient

X

X

X

ACP Self-efficacy

ACP Self-efficacy Scale (ACP-SE) [25]

• 17 items

• Reported on an overall average 5-point Likert scale (range 1–5)

• 1 additional general item including all advance care planning can be used for comparison to the scale

GP

X

X

X

 Health-related quality of life

Short Form Health Questionnaire (SF-12v2) [26]

• Physical Health (PCS) and Mental Health (MCS) summary scores (range 0–100)

Patient

X

X

X

 Anxiety

Generalized Anxiety Disorder Questionnaire (GAD-7) [27]

• Sum score (range 0–21)

Patient

X

X

X

 Depression

Patient Health Questionnaire (PHQ-9) [28]

• Sum score (range 0–27)

Patient

X

X

X

 Appointment of a substitute decision maker

GP report

ACP engagement survey “readiness to sign official papers assigning a SDM” item

Patient

GP

X

X

X

 Completion of new ACP documents

Patient report

GP report

ACP engagement survey “readiness to sign official papers stating medical wishes” item

Patient

X

X

 Thinking about ACP

1 self-developed item, 10-point Likert (“How much have you thought about ACP in the last 3 months?”; response categories range from “not at all” to “very much”)

Patient

X

X

X

 Communication with the GP

4 self-developed items, 10-point Likert (e.g., “To what extent did the GP listen to your concerns about your future health?”; response categories range from “not at all” to “very much”)

Patient

X

X

X

 ACP Practices

• Next Steps training program questionnaire [29] (4 items)

• 2 items specific to practices with patients with chronic, life-limiting illness (“Which percentage of your patients has a chronic, life-limiting illness” and “With which percentage of your patients with a chronic, life-limiting illness do you conduct ACP conversations?”; 4 response options per item) [25]

• 8 additional items regarding ACP practices (e.g., “Where do the ACP conversations you conduct usually take place?”)

GP

X

X

X

 ACP Attitudes

Next Steps training program questionnaire [29]

• 9 items; 5-point Likert scale ranging from “Completely disagree” to “Completely agree”; adapted to the Belgian legal context

GP

X

X

X

 ACP Knowledge

Next Steps training program questionnaire [29, 30]

• 10 items; correct/not correct/don’t know; adapted to the Belgian legal context

GP

X

X

X

 Documentation of ACP discussion outcomes

Documentation template review

GP

X

X

 Level of engagement with ACP

ACP Engagement Survey, substitute decision maker version [31]

• 17 items; 5-point Likert scales

• 3 domain scores (“Serving as SDM”, “Contemplation”, Readiness”) computed as the unweighted average of items per domain (range 1–5)

SDM

X

X

X

 Demographic information

For patients and surrogate decision makers:

• Gender

• Age

• Marital status

• Highest completed education

• Religion

• Patient/SDM relationship

• Whether patient and SDM live together or apart

For patients:

• Previous completion of any advance directives (“wilsverklaringen”)

For surrogate decision makers:

• How long they have known the patient

For GPs:

• Gender

• Age

• Graduation year

• Practice setting(s)

• Years of experience as a GP

• Graduating university

• Working in a palliative home care team (yes/no)

• Working as a “coordinating and advising practitioner” in a residential care facility (yes/no)

• Prior formal ACP education or training (intensive/introductory/none)

• Prior formal palliative care education or training (intensive/introductory/none)

GP

Patient

SDM

X

 RE-AIM domain

Operationalization

 Reach

• Comparing the characteristics of participating patients with non-participants

 Efficacy/effectiveness

• Primary and secondary outcomes of the RCT

 Adoption

• ACP discussion documents uploaded

• Patient use of the work booklet

• Experiences of GPs and patients applying intervention steps

• Changes in GP practice

 Implementation

• Fidelity: the extent to which the steps of the intervention were followed as specified in the protocol

• Patient and GP barriers/facilitators to following the steps of the intervention

• Satisfaction of GPs and patients with the intervention components

 Maintenance

• GP intention for using the intervention materials in the future

• Recommendations by the GP and patients to improve intervention usability in the future