Understanding of an aggregate probability statement by patients who are offered participation in Phase I clinical trials.

Background: There is concern that patients with poor numeracy may have difficulty understanding the information necessary to make informed treatment decisions. The authors sought to characterize a special form of numeracy among patients with advanced cancer who were offered participation in Phase I oncology clinical trials.

Methods: Surveys were administered to 328 cancer patients who were considering Phase I trials. Their frequency-type numeracy was assessed using a multiple-choice question involving a hypothetical scenario in which a physician stated that an experimental treatment would control cancer in "40% of cases like yours." In univariate and multivariable analyses, patient characteristics that were associated with better numeracy were identified.

Results: The correct frequency-type interpretation was selected by 72% of respondents. Fourteen percent of respondents incorrectly selected a belief-type answer, "The doctor is 40% confident that the treatment will control my cancer." In a multivariable model, patients who answered incorrectly tended to have less formal education and less experience with experimental therapies.

Conclusions: Because the misunderstandings some patients demonstrated may influence their treatment decision making adversely, it is critical to identify such patients and to give them special consideration when communicating information about potential risks and benefits of treatment.