Open Access Open Badges Study protocol

A brief tool to assess capacity to consent for medical care among homeless individuals with problematic substance use: study protocol

Darlene Taylor1*, Louise Masse2, Anita Ho3, Michael L Rekart4, Mark Tyndall5, Bonnie Henry1, Joanne Clifton6, Laurenna Peters1, Gina Ogilvie1 and Jane Buxton1

Author Affiliations

1 BC Centre for Disease Control, University of British Columbia, 655 West 12th Avenue, Vancouver, BC, V5Z 4R4, Canada

2 Department of Pediatrics/School of Population and Public Health, University of British Columbia, 4480 Oak Street, L408, Vancouver, BC, V6H 3V4, Canada

3 Centre for Applied Ethics, University of British Columbia, 6356 Agricultural Road, Vancouver, BC, V6T 1Z2, Canada

4 School of Population and Public Health, University of British Columbia, 2206 East Mall, Vancouver, BC, V6T 1Z3, Canada

5 Department of Infectious Diseases, University of Ottawa, 75 Laurier Avenue East, Ottawa, ON, K1N 6N5, Canada

6 Department of Surgery, University of British Columbia, 899 West 12th Avenue, Vancouver, BC, V5Z 1M9, Canada

For all author emails, please log on.

Archives of Public Health 2013, 71:11  doi:10.1186/0778-7367-71-11

Published: 8 May 2013



Public health care increasingly uses outreach models to engage individuals who are marginalized, many of whom misuse substances. Problematic substance use, together with marginalization from the health care system, among homeless adults makes it difficult to assess their capacity to consent to medical care. Tools have been developed to assess capacity to consent; however, these tools are lengthy and unsuitable for outreach settings. The primary objective of this study is to develop, validate, and pilot a brief but sensitive screening instrument which can be used to guide clinicians in assessing capacity to consent in outreach settings. The goal of this paper is to outline the protocol for the development of such a tool.


A brief assessment tool will be developed and compared to the MacArthur Competency Assessment Tool for Treatment (MacCAT-T). As list of 36 possible questions will be created by using qualitative data from clinician interviews, as well as concepts from the literature. This list will be rated by content experts according to the extent that it corresponds to the test objectives. The instrument will be validated with 300 homeless adult volunteers who self-report problematic substance use. Participants will be assessed for capacity using the MacCAT-T and the new instrument. A combination of Classical Test Theory and advanced psychometric methods will be used for the psychometric analysis. Corrected Item-Total correlation will be examined to identify items that discriminate poorly. Guided exploratory factor analysis will be conducted on the final selection of items to confirm the assumptions for a unidimensional polytomous Rasch model. If unidimensionality is confirmed, an unstandardized Cronbach Alpha will be calculated. If multi-dimensionality is detected, a multidimensional Rasch analysis will be conducted. Results from the new instrument will be compared to the total score from the MacCAT-T by using Pearson’s correlation test. The new instrument will then be piloted in real-time by street outreach clinicians to determine the acceptability and usefulness of the new instrument.


This research will build on the existing knowledge about assessing capacity to consent and will contribute new knowledge about assessing individuals whose judgment is impaired by substance use.

Capacity to consent; Substance use; Psychometric instruments; Vulnerable populations