Dose-Response Effects of Mindfulness Meditation

Psychological well-being will be assessed using the Warwick-Edinburgh Mental Well-being Scale (WEMWBS), which includes 14 positively worded items of mental well-being for the past 2-weeks, on a 5-point Likert scale from 1 (None of the time) to 5 (All of the time).

Psychological distress will be assessed using the Kessler Psychological Distress Scale (K10), a 10-item self-report measure of psychological distress over the past month, on a 5-point Likert scale from 1 (None of the time) to 5 (All of the time)

Anxiety will be assessed using (i) the PROMIS Anxiety Short Form, a 7-item measure of the pure domain of anxiety over the past 7 days, on a 5-point Likert scale from 1 (Never) to 5 (Always), and (ii) the Anxiety subscale of the Depression, Anxiety and Stress Scale (DASS-21), a 7-item measure of anxiety over the past 7 days, on a 4-point Likert scale from 0 (Did not apply to me at all - never) to 3 (Applied to me very much, or most of the time).

Depression (secondary outcome) will be assessed at T0, T0.5, T1, and T2 using the PROMIS Depression Short Form, an 8-item measure of depression over the past 7 days, on a 5-point Likert scale from 1 (Never) to 5 (Always).

Nonattachment will be assessed using the Nonattachment Scale (NAS-7, which measures the Buddhist notion of nonattachment on a 7-point Likert scale from 1 (Disagree strongly) to 5 (Agree strongly).

Trait Mindfulness will be assessed with the Five Facet Mindfulness Questionnaire (FFMQ), a 15-item measure that includes five factors representing elements of mindfulness, on a 5-point Likert scale from 1 (Never or very rarely true) to 5 (Very often or always true)

Decentering (secondary outcome) will be assessed at T0, T0.5, T1, and T2 using the Experiences Questionnaire (EQ), an 11-item measure of decentering, on a 5-point Likert scale from 1 (Never) to 5 (All the time).

Equanimity will be assessed with the Two Factor Equanimity Scale (EQUA-S), a 14-item measure of equanimity, on a 5-point Likert scale from 1 (Never) to 5 (Very often or always).

Repetitive negative thoughts will be assessed with the Repetitive Negative Thoughts Questionnaire (RNTQ), a 22-item measure of repetitive negative thinking, on a 6-point Likert scale from 1 (Not at all typical of me) to 6 (Extremely typical of me)

Emotional Reactivity will be assessed using the Perth Emotional Reactivity - Short Form (PERS-S), an 18-item measure of the activation, intensity, and duration of one's emotional responses, on a 5-point Likert scale from 1 (Very unlike me) to 5 (Very like me)

Attention Control will be assessed with the Attention Control Scale - Short-Form (ATTC-SF), a 10-item measure that includes two subscales of attention (shifting and focusing), on a 4-point Likert scale ranging from 1 (Almost never) to 4 (Always).

Emotional Regulation measured by the Perth Emotional Reactivity - Short Form (PERS-S), an 18-item measure of the activation, intensity, and duration of one's emotional responses on a 5-point Likert scale from 1 (Very unlike me) to 5 (Very like me).

Social Anxiety will be assessed with the Social Anxiety Disorder Severity Scale (SAD-D), a 10-item measure assessing the severity of symptoms of social anxiety in the past 7 days on a 5-point Likert scale from 0 (Never) to 4 (All of the time).

Sleep will be measured by the single-item Sleep Quality Scale on a 10-point Likert scale: Terrible (1), Poor (2-4), Fair (5-7), Good (7-9) to Excellent (10)

Momentary mood will be assessed daily, before and after each meditation session with a modified English version of the Multidimensional Mood Questionnaire (MDMQ). The MDMQ assesses valence, arousal, and calmness dimensions of momentary mood using six items on a 7-point Likert scale (with end-points labelled "very"). Participants will respond to the statement "At this moment I feel:" 1. tired-awake; 2. content-discontent; 3. agitated-calm; 4. energetic-lacking energy; 5. well-unwell; 6. relaxed-tense.

State mindfulness will be assessed with a brief 6-item version of the State Mindfulness Scale (SMS) on a 5-point Likert scale with options ranging from 1 (Not at all) to 5 (Very well).

Attention will be assessed with the attention regulation and self-regulation subscales of the Multidimensional Assessment of Interoceptive Awareness (MAIA) on a 6-point Likert scale ranging from 1 (Never) to 6 (Always).

Decentering will be assessed with a brief 5-item version of the Decentering Subscale of the Toronto Mindfulness Scale (TMS) on a 6-point Likert scale ranging from 1 (Not at all) to 6 (Very much).

Mindful attitudes will be assessed using a face-valid selection of: a) TMS items to reflect attitudes of non-judgement (acceptance/allowance) and curiosity; b) a selection of FFMQ non-judgement subscale items to reflect non-judgement (non-evaluative aspect); c) and NAS-7 items to reflect non-attachment using a 5-point Likert scale ranging from 1 (Not at all) to 5 (Very much).