Measuring the Impact of Quantitative Information on Patient Understanding: Approaches for Assessing the Adequacy of Patient Knowledge about Colorectal Cancer Screening

Background. Guidelines recommend that decision aids disclose quantitative information to patients considering colorectal cancer (CRC) screening, but the impact on patient knowledge and decision making is limited. An important challenge for assessing any disclosure involves determining when an individual has “adequate knowledge” to make a decision. Methods. We analyzed data from a trial that randomized 213 patients to view a decision aid about CRC screening that contained verbal information (qualitative arm) versus one containing verbal plus quantitative information (quantitative arm). We analyzed participants’ answers to 8 “qualitative knowledge” questions, which did not cover the quantitative information, at baseline (T0) and after viewing the decision aid (T1). We introduce a novel approach that defines adequate knowledge as correctly answering all of a subset of questions that are particularly relevant because of the participant’s test choice (“Choice-Based Knowledge Assessment”). Results. Participants in the quantitative arm answered a higher mean number of knowledge questions correctly at T1 than did participants in the qualitative arm (7.3 v. 6.9, P < 0.05), and they more frequently had adequate knowledge at T1 based on a cutoff of 6 or 7 correct out of 8 (94% v. 83%, P < 0.05, and 86% v. 71%, P < 0.05, respectively). Members of the quantitative group also more frequently had adequate knowledge at T1 when assessed by Choice-Based Knowledge Assessment (87% v. 76%, P < 0.05). Conclusions. Patients who viewed quantitative information in addition to verbal information had greater qualitative knowledge and more frequently had adequate knowledge compared with those who viewed verbal information alone, according to most ways of defining adequate knowledge. Quantitative information may have helped participants better understand qualitative or gist concepts. Trial Registration: ClinicalTrials.gov ID# NCT01415479 HIGHLIGHTS: Patients who viewed quantitative information in a decision aid about colorectal cancer screening were more knowledgeable about nonquantitative information and were more likely to have adequate knowledge according to a variety of approaches for assessing that, compared with individuals who viewed only qualitative information. This result supports the inclusion of quantitative information in decision aids. Researchers assessing patient understanding should consider a variety of ways to define adequate knowledge when assessing decision quality.