The active condition, "Project WAVE," (Wise Awareness of Visiting Emotions) includes 1) an introduction to the program's rationale; 2) psychoeducation about emotion dysregulation, avoidance, and exposure; 3) testimonials from others who describe their experience facing a difficult emotion; 4) an emotion exposure task along with an audio-guided nonreactivity practice; and 5) the creation of a personalized "action plan" usable for continued practice. Project WAVE is designed to take approximately 15-20 minutes.

The control condition is self-administered and structurally similar to Project WAVE (e.g., includes peer narratives and contains a similar number of writing activities). It is designed to control for non-specific aspects of supportive online activities. The activity involves an emotionally neutral writing task (journaling about daily life events). This control condition is designed to take approximately 10-15 minutes.

Project WAVE is an online, self-directed single-session intervention designed to foster emotional nonreactivity skills in young adults aged 18-29.

Emotion intolerance beliefs will be measured using the Emotion Avoidance Questionnaire (EAQ) Beliefs subscale, a five-item self-report measure of a participant's beliefs about their inability to tolerate emotions (Taylor et al., 2004). Participants will rate their agreement with each statement reflecting how they feel "right now" on a five-point scale. A higher score indicates greater levels of negative beliefs about their ability to tolerate emotions.

Perception of the intervention's utility in teaching nonreactivity will be assessed with the items: "During this activity, to what extent were you able to observe your emotions without getting caught up in them?"; "How much did this activity help you learn how to be nonreactive to distressing emotions?"; "How much do you think being nonreactive to distressing emotions could help you in the future?" (each on a five-point Likert scale ranging from "not at all" to "very much"); and "How likely are you to try being nonreactive to distressing emotions in the future?" (on a five-point Likert scale ranging from "very unlikely" to "very likely"). Participants will also be asked a multi-select question: "Did anything get in the way of being able to complete the nonreactivity practice?" with response options including "It was too hard," "It was confusing," "I didn't find it interesting," "I got distracted," "Something else [write-in]," or "Nothing got in the way."

Nonreactivity to emotions will be measured using a three-item subset of the Five Facet Mindfulness Questionnaire (FFMQ) Nonreactivity subscale, a seven-item self-report measure of a participant's tendency to react to their emotions (Baer et al., 2008). We are choosing to use a slightly modified three-item subset that has been used in previous research (Galla et al., 2020). For the present purposes, we used "emotions" in place of the original "thoughts or images" because the intervention focuses both on thoughts and body sensations. Participants in both conditions will rate their agreement with each statement reflecting how true each statement was for them over the past two weeks on a five-point scale.