Table 1 Description of how the qualitative component addressed features of trustworthiness criteria

Credibility (internal validity)

Familiarity and rapport between the interviewer (JMK), dance instructors and participants was developed over four visits to each school. By observing dance sessions an understanding of the content and delivery was established. This insight informed the refinement of interview guides and may have encouraged honesty in the interviews. Researcher bias in the selection of participants was minimised by a random selection of focus group participants by attendance. Views from all intervention schools were gathered. During analysis, frequent study team de-briefings ensured different interpretations of data were considered.

Transferability (external validity) and dependability (reliability)

Findings should be understood within the study context. However, if similar findings are elicited in different schools or interventions, this could demonstrate a degree of transferability. By providing in-depth details of the methods we ensure that the study is repeatable.

Confirmability (Objectivity)

Researchers (JMK, SJS, TM, MJE) worked to ensure that the findings reflected the experiences of participants. SJS and RJ developed the project and SJS uses SDT in his research. JMK attended four dance sessions within each school and became familiar with each school setting. Therefore this may have influenced her interpretation of qualitative information. TM did not perform any school visits and does not have a background in SDT. Therefore he was able to assume a role of checking that interpretations reflected the data.