Background Plain language summaries (PLSs) are intended to provide readers with a clear, nontechnical, and easily understandable overview of medical and scientific literature; however, audience preferences for specific PLS formats have yet to be fully explored. Objective This study aims to evaluate the preferred readability level and format for PLSs of medical research articles of different disease states via a web-based survey of audiences of different age groups. Methods Articles describing phase III clinical trials published in top-level, peer-reviewed journals between May 2016 and May 2018 were identified for 3 chronic disease states representing a range of adult patient age groups: (1) psoriasis, a skin disease representative of younger patients; (2) multiple sclerosis (MS), a neurological disease representative of middle-aged patients; and (3) rheumatoid arthritis (RA), a painful joint disease representative of older patients. Four PLSs were developed for each research article, of which 3 were text-only summaries (written with high, medium, and low complexity) and 1 was an infographic. To evaluate each of the 4 PLS formats, a 20-question open survey (specific to one of the 3 diseases) was sent to a representative sample selected via UK-based patient association websites, Twitter, and Facebook patient groups. A weighted-average calculation was applied to respondents’ ranked preferences for each PLS format. Results For all 3 articles, the weighted-average preference scores showed that infographic (psoriasis 2.91, MS 2.71, and RA 2.78) and medium-complexity text-based PLS (reading age 14-17 years, US Grade 9-11; psoriasis 2.90; MS 2.47; RA 2.77) were the two most preferred PLS formats. Conclusions Audience preferences should be accounted for when preparing PLSs to accompany peer-reviewed original research articles. Oversimplified text can be viewed negatively, and graphical summaries or medium-complexity text-based summaries appear to be the most popular. Plain Language Summary Patients and caregivers should have the chance to read about medical research in a format they can understand. However, we do not know much about the formats that people with different illnesses or ages prefer. Researchers wanted to find out more about this. They selected 3 medical articles about illnesses that affect different age groups: psoriasis (younger patients), multiple sclerosis (middle-aged patients), and rheumatoid arthritis (older patients). They created 4 summaries of each article. One was a graphical summary, and the other 3 were words-only summaries of high, medium, and low complexity. Then, the researchers posted surveys on UK patient group websites and Facebook patient groups to ask people what they thought of the summaries. The surveys were taken by 167 people. These people were patients with psoriasis, multiple sclerosis, or rheumatoid arthritis, or their caregivers. Most were women, and about half had a university degree. For each illness, most people preferred the graphical summary. Among the word-only summaries, most people preferred the medium-complexity wording written for a reading age of 14 to 17 years. People felt that the graphical and medium-complexity summaries were clear and concise, while the others used jargon or were too simple. Authors of medical articles should remember these results when writing summaries for patients. More research is needed about the preferences of other people, such as those with other illnesses. (See Multimedia Appendix 1 for the graphical summary of the plain language summary.)

BACKGROUND Plain language summaries (PLS) are intended to provide readers with a clear, non-technical, and easily understandable overview of medical and scientific literature; however, audience preferences for specific PLS format have yet to be fully explored. OBJECTIVE To evaluate the preferred readability level and format for PLS of medical journal articles across different disease states, with online audiences from various age groups. METHODS Articles describing phase III clinical trials from top-level, peer-reviewed journals published between May 2016–May 2018 were identified for three disease states representing a range of patient age groups (psoriasis, a skin disease [younger patients]; multiple sclerosis [MS], a nerve-based disease [middle-aged patients]; and rheumatoid arthritis [RA], a painful joint disease [older patients]). Four PLS were developed for each article: three as text only (written with high-, medium-, and low-complexity) and one as an infographic. To evaluate each of the four PLS formats, a 20-question survey (specific to one of the three diseases) was sent to a representative sample, via UK-based patient association websites, Twitter, and Facebook patient groups. A weighted-average calculation was applied to responders’ ranked preferences for each PLS format. RESULTS Across all three diseases, the weighted-average preference scores showed that infographics (psoriasis=2.91; MS=2.71; RA=2.78) and medium-complexity text PLS (reading age: 14–17 years, US Grade 9–11; psoriasis=2.90; MS=2.47; RA=2.77) were the two most-preferred PLS formats in each case. CONCLUSIONS Audience preferences should be accounted for when preparing PLS to accompany original peer-reviewed research articles. Oversimplified text can be viewed negatively, and infographic versions or medium-complexity text appear to be the most popular.