Background Significant gaps exist between guidelines-recommended therapies for 
cardiovascular disease prevention and current practice. Fixed-dose combination 
pills ('polypills') potentially improve adherence to therapy. This study is a 
preference study undertaken in conjunction with a clinical trial of a polypill 
and seeks to examine the underlying reasons for variations in treatment 
adherence to recommended therapy. Methods/design A preference study comprising: 
(1) Discrete Choice Experiment for patients; and (2) qualitative study of 
patients and providers. Both components will be conducted on participants in the 
trial. A joint model combining the observed adherence in the clinical trial 
(revealed preference) and the Discrete Choice Experiment data (stated 
preference) will be estimated. Estimates will be made of the marginal effect 
(importance) of each attribute on overall choice, the extent to which 
respondents are prepared to trade-off one attribute for another and predicted 
values of the level of adherence given a fixed set of attributes, and contextual 
and socio-demographic characteristics. For the qualitative study, a thematic 
analysis will be used as a means of exploring in depth the preferences and 
ultimately provide important narratives on the experiences and perspectives of 
individuals with regard to adherence behaviour. Ethics and dissemination Primary 
ethics approval was received from Sydney South West Area Health Service Human 
Research Ethics Committee (Royal Prince Alfred Hospital zone). In addition to 
usual scientific forums, the findings will be reported back to the communities 
involved in the studies through site-specific reports and oral presentations.