The influence of varying cost formats on preferences

Background. Numerous studies have found that cost strongly influences patients' decision making. The objective of this study was to explore the impact of varying cost formats on patients' preferences. Methods. Mechanical Turk workers completed a choice-based conjoint (CBC) survey. The CBC survey was designed to examine stated preferences for the use of second-line agents to treat diabetes across 5 attributes: route of administration, efficacy, risk of low blood sugar, frequency of checking blood sugar levels, and cost. We developed 7 versions of the CBC survey that were identical except for the cost attribute. We described cost in terms of: Affordability, Monthly Co-pay, Dollar Sign Rating, How Expensive, or How Cheap compared with other medications, Working Hours Equivalent (per mo) and Percent of Monthly Income. The resulting part-worth utilities were used to calculate the relative importance of cost and to estimate treatment preferences for exenatide, a sulfonylurea, and insulin. Results. The relative impact of cost varied significantly across the 7 formats. Cost had the greatest influence on participants' decisions when framed in terms of Affordability [mean (SD) relative importance, 37.3 (0.9)] and the lowest influence when framed in terms of How Cheap (compared with other drugs) [12.1 (0.9)]. A sulfonylurea was strongly preferred across 4 of the 7 formats. Preference for insulin, the most effective, albeit riskiest, option was low across all cost formats. Conclusions. The format used to describe cost affects how the attribute impacts patients' preferences. Individuals are most cost-sensitive when cost is framed in terms of affordability and least cost-sensitive when cost is described in terms of how cheap the medication is compared with others.