Study design

A three-arm randomized control trial was conducted for comparison between 1) active intervention group (both counseling by primary care physicians and patient education pamphlets), 2) passive intervention group (only patient education pamphlets), and 3) control group (usual care). The counseling by primary care physicians has two components. Firstly, primary care physicians counsel the patients in clinics. The counseling is structured according to the official public material (pamphlets) produced by the Ministry of Health, Singapore which covers concept of and terms surrounding ADs, the process of making ADs, and closely linked concepts such as terminal illness and palliative care [26] (Supplementary File 3). The pamphlets are in all four major languages used by Singapore residents (English, Mandarin, Malay and Tamil). Secondly, participants were given time for open-ended discussions and clarifications. Participants were given the pamphlets at the end of the counseling sessions. Participants in the passive intervention group were only given the pamphlets during their routine clinic consult by their primary care physicians but no active counseling on ADs were conducted.

Randomization was performed via block randomization with Sequential Numbered Opaque Sealed Envelopes (SNOSE), in variable blocks of 6 and 9, in a ratio of 1:1:1. At 6-weeks follow-up, phone recall was performed by a blinded member of the study team to assess the study outcomes (see Outcome Measures). A participant was considered a non-responder if the individual was unable to be contacted by phone call after 3 attempts on separate days or had requested to withdraw from the study prior to the 6-weeks mark. The study was conducted in accordance of the CONSORT 2010 checklist for randomized controlled trials (Suplementary File 1) [27].

Participants were recruited during routine clinic visits from four polyclinics in Singapore (Bedok, Marine Parade, Outram, Tampines). Polyclinics are large public primary care clinics located throughout Singapore that provide subsidized primary care [28]. Patients first attended their regular clinic visits during which primary care physicians invited the eligible patients to participate in the study and explained the trial as per trial protocol (Supplementary File 2). Interventions were conducted during the same clinic visit if patients gave consent to participate in the study. All participants were aged > 40 years and were patients of the aforementioned polyclinics. Exclusion criteria were known history of mental illness including depression and dementia, known diagnosis of terminal illness, and participants who had previously signed an AD or undergone ACP discussions. Trial duration is 29 March to 19 Dec 2018. Briefing sessions were conducted with the participating primary care physicians to ensure the adherence to the study design and protocol prior to recruiting patients. We also ensured consistency of the interventions in our study by the use of a checklist of discussion points based on the official public material (pamphlets) produced by the Ministry of Health, Singapore (Supplementary File 3).

Data on participants’ past medical history were obtained through electronic medical records. Baseline data of all participants were collected during the enrolment. Informed consent was obtained prior to enrolment.