Acceptance and Commitment Therapy for Informal Caregivers of People With Dementia

Measure the emotional states of depression, anxiety and stress will be assessed by DASS-21 self-report questionnaire. DASS-21 has three sections (7-items per section) that measure depression, anxiety, and stress on a 4-point Likert scale (0= the statement did not apply to me at all, 4= the statement applied to me very much or most of the time. DASS-21 is a validated scale that has been used in previous studies and has been recommended for measuring the dimensions of depression, anxiety, and stress.

Informal caregivers' sense of competence indicates the feelings of being capable of caring for a person with dementia. Short Sense of Competence Questionnaire (SSCQ) is a valid and reliable scale which has been used in previous studies with a similar target population and consists of seven items rated on a 5-point scale from 1 ("agree very strongly") to 5 ("disagree very strongly")

The Caregiver Self-Efficacy Scale (CSES) is based on a Dutch adaptation of the Lorig et al. CSES evaluates caregiver self-efficacy (four item) and service-use self-efficacy (five items) and item scores range from 1 (uncertain) to 10 (very certain). Previous research has shown that CSES is valid and reliable

Caregiver burden will be measured by a one-item questionnaire. The perseverance-time question will ask: if the informal caregiver's current situation persists, for how long (in month) the informal caregiver thinks they are able to maintain caregiving. This questionnaire is a good predictor for institutionalisation.

Will be assessed qualitatively during a semi-structured interview based on Program Participation Questionnaire (PPQ)

Brief self-report feasibility questionnaire

Will be assessed qualitatively during the semi-structured interview

Number of drop outs of study after collecting informed consent

Will be assessed qualitatively during coaching sessions

Psychological flexibility is defined as the ability to be accepting, flexible and conscious in facing challenging situations and the ability to stay engaged with valued activities. This factor will be assessed by Acceptance and Action Questionnaire II, (AAQ-II) which has been reported to be valid, reliable and psychometrically consistent . 10 Items are scored on a 7-point Likert scale and higher scores indicate more psychological flexibility

Changes in psychological flexibility and functional coping with negative thoughts and feelings in informal caregivers will be assessed using the Flexibility Index Test (FIT-60). This reliable and valid questionnaire will assess six different ACT processes (acceptance, diffusion, self as context, attention to present moment and values, and dedicated action) and can monitor the progress of the ACT therapy. The questionnaire consists of 60 items and is scored on a seven-point Likert scale (0= completely disagree, 6= completely agree). Higher score reflects on higher psychological flexibility.

Important areas of life will be identified by the Valued Living Questionnaire (VLQ), which individuals rate level of importance of 12 different areas (e.g. family, work) on 10-point Likert scale (1= the area is not important at all, 10= the area is very important). The most important area will be considered as individuals' "value" at their current stage of life. The psychometric properties have been investigated in previous studies.

The extent to which individuals have been actively living in accordance with their values will be assessed by the Engaged Living Scale (ELS). ELS has been recommended for assessing committed actions and value engagement . ELS consists of 16-items in which individual should reflect in statements based on 5-point Likert scale (1=strongly disagree, 5= strongly agree)

Goal-attainment scaling will be conducted qualitatively and will be measured as part of the weekly coaching and booster sessions. Level of goal achievement since the last coaching session and the extent to which participants could achieve their goals at expected level will be discussed