As part of demonstrating patient understanding, the FDA PRO Guidance calls for the assessment of instruments’ readability within the target population, citing that evaluation of readability is subject to review. However no specific readability tests are recommended. This study aimed to identify appropriate readability assessments for the evaluation of COAs.

Existing readability tests were identified and evaluated based on their ability to assess the syntax of COAs, as well as their applicability to patient-facing reading materials. Selected tests were applied to existing COAs to evaluate readability and determine if they were appropriate for COA readability assessment.

The New Dale-Chall Readability Formula was designed for evaluating health education materials and is recommended for initial evaluation of a COA to identify US grade level readability, as well as highlight words that are key drivers of readability difficulty. Each difficult word identified should be evaluated in the context of the target population (i.e., disease-specific terms may be familiar to them but not general population) as well as with regard to measurement (i.e., language in a response scale may be difficult on its own but not in relation to other response options). The Flesch-Kincaid readability test can be used to provide additional readability insight for COA instructions and items that are rated poorly by the Dale-Chall test.

Use of the Dale-Chall and Flesch-Kincaid readability tests is the recommended approach for evaluation of the readability of COAs, but should be adapted as needed depending on the target populations. Readability should be assessed throughout the COA development process (e.g., problematic words flagged by tests can be explored with patients during cognitive interviews); factors contributing to poor readability should be considered as early as item generation. Further guidance on suitable readability assessments is recommended, in the event these are critical to the review of a COA’s adequacy.