Table 1 Intervention development phases and associated tasks

1. Select and appraise the best available scientific research and evidence.

• Critically evaluated extant literature to identify key risk and protective factors for body image among Brazilian adolescents.

• Concurrently, UNICEF conducted 26 workshops with 681 (66% girls) ethnically diverse Brazilian adolescents across 15 northern and south-eastern cities to better understand the nature of, and influences on, their body image, and their preferences for the chatbot’s key messages and persona [34].

2. Apply the evidence in a collaborative decision-making process with relevant parties.

• Data from the literature review and focus groups informed a collaborative decision-making process between academics, industry partners and UNICEF to select which risk and protective factors would be targeted within the chatbot.

• Three themes were agreed upon: 1) Unrealistic beauty standards perpetuated by society; 2) Appearance pressures experienced within interpersonal relationships; 3) Acceptance and appreciation of one’s body.

3. Selection and adaptation of extant techniques that target the agreed upon themes, for use in the chatbot.

• A micro-intervention framework was used to identify and select therapeutic techniques that addressed the above themes [35].

• Techniques needed to be brief (e.g., completed in under 10 min), standalone (e.g. a distinct beginning and end), immediately actionable (e.g., can be executed in the moment, without additional resources) and adaptable for digital platforms.

• Researchers drew on their expertise of working with evidence-based body image prevention and intervention approaches and a meta-analysis on therapeutic change techniques to identify and select appropriate techniques [31].

• Eight techniques (see Table 2) were extracted from extant evidence-based body image programs, including: Confident Me [36], The Body Image Workbook [37], and Expand Your Horizon [38].

• A script was developed for each technique and was reviewed by body image experts from Brazil and the UK, as well as Dove and UNICEF.

• Scripts were then amalgamated into a written interactive dialogue to be delivered by the chatbot fictional hosts, Dandara (a young Brazilian woman) and Gabriel (a young Brazilian man).

• Hosts’ gender and persona were informed by:

 ° Mixed-gender preferences observed among young people receiving body image interventions [39].

 ° Adolescents’ use of peers for emotional and informational support in online environments ([40]).

 ° Qualitative and quantitative data obtained by UNICEF via focus groups and an online survey via UReport with girls and boys name preferences.

4. Development of the digital interface

• The digital interface of the chatbot was constructed by communication and technology experts at Talk2U.

• This iterative process involved frequent reviews by adolescents, body image experts based in Brazil and the UK, Dove and UNICEF.

• Key design features included:

 ° The use of Facebook Messenger, an instant messaging app for smartphones, to host the chatbot.

 ° The use of interactive elements that enhance user engagement and saliency of key therapeutic messages, including check-in messages, multi-media stimuli (i.e., audio and video clips; emojis [a small digital image or icon used to express an idea or emotion]), virtual hosts and the gamification of intervention techniques.

 ° In regards to gamification (i.e., the use of game design elements in non-game contexts, [41]), users needed to successfully complete a technique before progressing to the next technique within a thematic cluster. Gamification is used to incentivise users to continue their engagement while allowing them to master easier skills before progressing to more challenging tasks [42]. The ordering of techniques within each thematic cluster was informed by the researchers’ expertise, as well as feedback from further focus groups with adolescents on the acceptability and feasibility of the techniques and presentation formats.

• Project partners with technology and marketing expertise advised on the selection of the chatbot’s name, Topity.

• To reduce bias the institutional and industry affiliations were not displayed on the user interface. Participants and parents were, however, informed of the multi-international partnership and the relevant organisations involved in the ‘Parent and Participant Information & Consent’ form.

• Topity can be accessed via Facebook Messenger using the following URL link: https://www.facebook.com/topitychat/