1 Much of the health and medical information patients need for decision-making and disease self-management is 2 quantitative. Patients encounter numbers in lab results, medical risk information, genomic data, drug labels, 3 and medication instructions. Unfortunately, many patients, especially those with low health numeracy, have 4 difficulty understanding and using this information. Low health numeracy disproportionately affects health 5 disparities populations, yet is also prevalent among those with high health literacy. A large body of evidence 6 has identified information visualization and presentation approaches that improve patients' ability to understand 7 numbers. This evidence shows that patients' ability to interpret numbers is strongly influenced by presentation 8 (or format), such as whether a risk is described as 5% or 5 in 100, and whether laboratory data are listed in a 9 table or visualized as a graph with action thresholds. This research, if applied, could narrow disparities 10 between patients with high and low educational levels in their ability to understand and use their own health 11 data. However, evidence about numeracy has not been effectively translated from research settings to 12 healthcare. This failure impairs the effectiveness of information resources and information technology 13 interventions with patients with low numeracy. We will develop an interactive Communicating Numbers Clearly 14 guide to support professional decisions about presenting and visualizing numbers in health. This will require 15 conducting a systematic review to collate and evaluate current evidence; constructing a free online decision 16 support system for health educators, information technology developers, health information specialists, or 17 health professionals who create information resources for patients; and conducting an evaluation of the guide. 18 Our long-term goal is to establish Communicating Numbers Clearly as a training resource for individuals and 19 organizations that prepare health data for patients, and its application as a standard quality control step before 20 health numbers are released. Communicating Numbers Clearly will advance NLM's mission of supporting 21 consumer and patient engagement in understanding, accessing, and using their health data and other health 22 information resources. This project will produce: an evidence-based resource that integrates knowledge about 23 patient understanding of numbers in health; a freely available, interactive web-based system to help 24 information specialists make patient-centered decisions about information visualization and representation; and 25 a shareable ontology of numerical communication concepts available to support future development of 26 additional information resources and services to support patients, educators, and clinicians.