Improving patient understanding of prenatal screening tests: Using naturally sampled frequencies, pictures, and accounting for individual differences.

Objective: Health professionals must communicate prenatal screening test results effectively to patients, but these tests involve very low prevalence and high false positive risks; a situation known to be difficult for people to understand. Methods: The present experiments evaluated the effectiveness of presenting prenatal screening test results for Trisomy 21, Trisomy 13, or DiGeorge Syndrome, using either naturally sampled frequencies or standard percentages. Participants were given a task of interpreting the posterior probability of an embryo having the condition. Results: People were significantly better with naturally sampled frequencies. Numerical literacy and visuospatial ability significantly accounted for individual differences in performance within conditions. Participants nevertheless did not differ in ratings of how useful the different presentation formats were, suggesting a lack of awareness of how format influenced understanding. These results held regardless of whether the respondents were undergraduates (Experiment 1) or members of the general population recruited online (Experiment 2). Conclusion: Using naturally sampled frequencies improves patient understanding of prenatal screening tests results, with low cost of implementation. Innovation: Using realistic prenatal screening test results, these results show how to improve patient counseling via the use of naturally sampled frequencies.