Competing interests: All authors have completed the Unified Competing Interest form (available on request from the corresponding author) and declare: that VW reports a grant from the Canadian Institutes of Health Research and a grant from the Ontario Early Researcher Award during the conduct of the study; RC reports grants from NIHR during the conduct of the study, and LC reports that his employer is the Pan American Health Organisation, which is part of the World Health Organization, an intergovernmental organisation that is part of the UN system. Tackling health equity issues is in the mission and vision of the organisation. His salary is paid from the organisation’s budget, which is approved and funded by PAHO and WHO member states. His work includes monitoring and supporting the advancement of the Policy on Research for Health CD49/10 that specifically calls for the development of methods and better reporting of equity issues in research. The funders had no role in the study design. There were no other relationships or activities that could appear to have influenced the submitted work.