Gollwitzer 2018.

Study characteristics
Methods	Study design: randomised controlled trial Study grouping: parallel group
Participants	Baseline Characteristics Mental contrasting with implementation intentions‐ MCII Age (mean ± SD): NR Sex (N (% female)): NR Sample size: 41 Years of experience (mean ± SD): NR Mental contrasting with implementation intentions + further intervention groups ‐ IIMCII Age (mean ± SD): NR Sex (N (% female)): NR Sample size: 41 Years of experience (mean ± SD): NR Control Age (mean ± SD): NR Sex (N (% female)): NR Sample size: 47 Years of experience (mean ± SD): NR Overall Age (mean ± SD): 40 ± 10.2 Sex (N (% female)): 86 (82%) Sample size: 129 Years of experience (mean ± SD): 17.6 (NR) Included criteria: NR Excluded criteria: NR Pretreatment: There were no significant differences between the two groups for age, years of experience, or years working Compliance rate: NR Response rate: of 251 eligible participants 129 participated > 51% Type of healthcare worker: various healthcare workers
Interventions	Intervention characteristics Mental contrasting with implementation intentions ‐ MCII Type of the intervention: Intervention type 1 ‐ to focus one’s attention on the experience of stress Description of the intervention: Engage in a mental exercise that (1) required specifying a wish related to reducing stress, (2) identifying and imagining its most desired positive outcome, (3) detecting and imagining the obstacle that holds them back, and (4) coming up with an if‐then plan on how to overcome it. The number of sessions: 3 Duration of each session on average: NR Duration of the entire intervention: 3 weeks Duration of the entire intervention short vs long: short Intervention deliverer: NR Intervention form: individual Mental contrasting with implementation intentions + further intervention groups ‐ IIMCII Type of the intervention: Intervention type 1 ‐ to focus one’s attention on the experience of stress Description of the intervention: Engage in a mental exercise that (1) required specifying a wish related to reducing stress, (2) identifying and imagining its most desired positive outcome, (3) detecting and imagining the obstacle that holds them back, and (4) coming up with an if‐then plan on how to overcome it. (5) plan where and when to perform MCII. The number of sessions: 3 Duration of each session on average: NR Duration of the entire intervention: 3 weeks Duration of the entire intervention short vs long: short Intervention deliverer: NR Intervention form: individual Control (no intervention) Type of the intervention: NA Description of the intervention: NA The number of sessions: NA Duration of each session on average: NA Duration of the entire intervention: NA Duration of the entire intervention short vs long: NA Intervention deliverer: NA Intervention form: NA
Outcomes	Perceived Stress Questionnaire‐ 20‐ PSQ‐20 Outcome type: ContinuousOutcome
Identification	Sponsorship source: NR Country: Germany Setting: Various health institutions Comments: NR Authors name: Peter M Gollwitzer Institution: Department of Psychology, New York University, New York, NY, United States Email: gabriele.oettingen@nyu.edu Address: NR Time period: NR
Notes	PSQ included in analysis 1.1. Intervention groups combined to create a single pair‐wise comparison
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The message also contained the email address of the experimenter whom the nurses should contact if they wanted to register for the study. Those who registered (N = 251 nurses) were contacted in return by the experimenter (again via email) and given access to the study website that had been created by using the soscisurvey.de data collection service. Participants who entered the website (N = 129) were randomly assigned to the three conditions of the study (MCII = 41, and IIMCII = 41, Control = 47)"
Allocation concealment (selection bias)	Unclear risk	Not mentioned.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Participants were not blinded.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Participants were not blinded whereas outcomes are self‐reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	105 of the 129 (81%) randomized participants answered the final questionnaire. Reasons not provided nor whether missing was at random.
Selective reporting (reporting bias)	Unclear risk	No registration, nor did we find one.
Other bias	Unclear risk	Data on participants' adherence to the MCII instructions and the frequency and context of participants using MCII is not described.