Table 3.

Examples of changes made to study materials and procedure following participant feedback [54].

Theme	Participant feedback as expressed by one or more participants	Changes made to the study based on feedback
Doing the digital intervention right	It is unclear what the next step is after filling out the baseline questionnaires, and after completing the assigned task. “What happens now?” (P1)	Added flowcharts that show the participant journey at the beginning and end of each module link that is sent out. It includes a green arrow with the text “You are here” to demonstrate where they are in the study and the next step.
Getting the data right	It is difficult to remember exactly how many intrusions one had in the last week (for the retrospective rating at baseline). (P1)	We kept this question as part of inclusion criteria and ask for a general estimate (ie, “have you had at least 2 intrusive memories in the last week”), but also added a baseline (week -1) daily electronic registration/diary of intrusive memories that participants are asked to complete during the week prior to filling in the baseline questionnaires and completing the intervention/control session.
Feeling that participation is alright	It looks like there are going to be a lot of questions in the SmartTrial list of questionnaires. [You] could lump some of the single-item, or shorter questionnaires together. (P3)	We did this with four questionnaires, where we combined two of them together twice. We also removed one of the work-related questionnaires.