Objective To identify characteristics (factors) about health technology assessment (HTA) decisions that are important to the public in determining whether public engagement should be undertaken and the reasons for these choices.

Design Focus groups using a nominal group technique to identify and rank factors relevant to public engagement in HTA decision-making. Thematic analysis was also undertaken to describe reasons underpinning participants’ choices and rankings.

Setting Members of the Australian general public.

Participants 58 people, aged 19–71 years participated in 6 focus groups.

Results 24 factors were identified by participants that were considered important in determining whether public engagement should be undertaken. These factors were individually ranked and grouped into 4 themes to interpret preferences for engagement. Members of the public were more likely to think public engagement was needed when trade-offs between benefits and costs were required to determine ‘value’, uncertainties in the evidence were present, and family members and/or carers were impacted. The role of public engagement was also seen as important if the existent system lacked transparency and did not provide a voice for patients, particularly for conditions less known in the community.

Conclusions Members of the public considered value, impact, uncertainty, equity and transparency in determining when engagement should be undertaken. This indicates that the public's preferences on when to undertake engagement relate to both the content of the HTA itself as well as the processes in place to support HTA decision-making. By understanding these preferences, decision-makers can work towards more effective, meaningful public engagement by involving the public in issues that are important to them and/or improving the processes around decision-making.