Effects of Open-label Placebos on COVID-related Psychological Health

Self-reported anxiety was measured using the PROMIS Emotional Distress - Anxiety - Short Form. The PROMIS Emotional Distress - Anxiety - Short Form is an 8-item self-report questionnaire that assesses anxiety over the past 7 days in adults. Participants rated each item on a 1 (never) to 4 (always) scale. Total score ranges from 8-40 with higher scores indicating greater anxiety.

Time frame: Anxiety symptom severity was measured at Baseline (Day 1), Midpoint (Day 7), and Endpoint (Day 14)

Self-reported COVID-19 related stress was measured using the COVID-19 Stress Scale. The Covid stress scale (CSS) is a 36-item self-report questionnaire that measures stress-related to COVID-19 (Taylor et al., 2020). Participants rated each item on a 0 (not at all) to 4 (extremely) scale. For the purposes of this study, only total scores were calculated. Total score ranges from 0-144 with higher scores indicating greater COVID-related stress.

Time frame: COVID-19 related stress was measured at Baseline (Day 1), Midpoint (Day 7), and Endpoint (Day 14)

Self-reported anxiety was measured using the Center for Epidemiological Studies - Depression (CES-D) Scale. The Center for Epidemiological Studies - Depression (CES-D) Scale is a 20-item self-report questionnaire that assesses depressive symptoms over the past 7 days. Participants rated each item on a 0 \[rarely or none at the time (less than one day)\] to 3 \[most or all of the time (5 to 7 days)\] scale. Total score ranges from 0-60 with higher scores indicating higher levels of depression.

Time frame: Depression symptom severity was measured at Baseline (Day 1), Midpoint (Day 7), and Endpoint (Day 14)

Self-reported perceived stress was measured using the Perceived Stress Scale (PSS). The Perceived Stress Scale (PSS) is a 10-item self-report questionnaire that assesses the extent to which different situations affect our perceptions of stress during the last month (Cohen, 1994). The scale was modified for the current study in order to measure ratings of perceived stress over the past 7 days. Participants rated each item on a 0 (never) to 4 (very often) scale. Total score ranges from 0-40 with higher scores indicating greater perceived stress.

Time frame: Perceived stress measured at Baseline (Day 1), Midpoint (Day 7), and Endpoint (Day 14)

Intervention acceptability was measured using the Acceptability of Intervention Measure (AIM; Weiner et al., 2017). The AIM is a 4-item self-report measure that assesses the extent to which an intervention is perceived to be satisfactory, adequate, and appealing. The items are averaged with scores ranging from 1-5 with higher numbers indicating that the OLP intervention is satisfactory and appealing.

Time frame: Ratings of intervention acceptability were measured at Endpoint (Day 14)

Population: Intervention acceptability was not measured in the No-Treatment Control group because they did not receive the treatment.

Intervention appropriateness was measured using the Intervention Appropriateness Measure (IAM; Weiner et al., 2017). The IAM is a 4-item self-report measure that assesses the extent to which an intervention is perceived to be fitting, relevant, and compatible with a population or setting to address a particular problem. The items are averaged with scores ranging from 1-5 with higher numbers indicating that the OLP intervention is perceived to be fitting, relevant, and compatible with a population or setting to address a particular problem.

Time frame: Ratings of intervention appropriateness were measured at Endpoint (Day 14)

Population: Intervention Appropriateness was not measured in the No-Treatment Control group because they did not receive the treatment.

Intervention feasibility was measured using the Feasibility of Intervention Measure (FIM; Weiner et al., 2017). The FIM is a 4-item self-report measure that assesses the extent to which an intervention can be successfully implemented within a given setting. The items are averaged with scores ranging from 1-5 with higher numbers indicating that the OLP intervention is easy to use and doable.

Time frame: Ratings of intervention feasibility were measured at Endpoint (Day 14)

Population: Intervention feasibility was not measured in the No-Treatment Control group because they did not receive the treatment.

Participants in the open-label placebo group were instructed to take two placebo pills a day for 14 days (28 placebo pills). Treatment adherence was measured as the percentage of placebo pills taken by each participant (number of pills taken / 28 \* 100).

Time frame: Treatment adherence was measured daily for 14 days beginning after intervention administration (Day 1).

Population: Treatment adherence was not measured in the No-Treatment Control group because they did not receive the treatment.

Participants in the open-label placebo group rated their expectations of the open-label placebo treatment using representative questions (10-items) from each sub-scale of the Treatment Expectations Questionnaire (TEX-Q; Alberts et al. (2020). Two subscales were calculated from exploratory factor analysis: Expected benefits and Expected harm. The range for expected benefits ranged from 0-10 with higher scores indicating greater benefits from the OLP. The range for expected harm also ranged from 0-10 with higher scores indicating expecting more harm.

Time frame: Treatment expectations were measured during the administration of the intervention (Day 1) and at the end of the study (Day 14)

Population: Participants in the No-Treatment Control group were not administered the Treatment Expectations Questionnaire because they did not receive any treatment.