ClinicalTrials.gov is a database designed to help clinical researchers make their research publicly available. The clinical trials registered on the database each include a brief summary, which is meant to be a short description that the public can easily understand. In September 2022, ClinicalTrials.gov published a "Plain Language Checklist for Lay Brief Summaries" on their website, which identifies plain language best practices intended to help investigators craft summaries that can be readily understood by the public. This thesis assesses the impact of the checklist on the language use in the brief summaries in the year following the checklist's publication. The analysis examines 62 brief summaries for Phase III and IV clinical trials posted on ClinicalTrials.gov between September 26, 2022, and September 26, 2023. It focuses particularly on summaries associated with rheumatoid arthritis, knee replacement, and conjunctivitis to gauge how well they complied with 4 of the 19 criteria on the Plain Language Checklist: keeping sentences and paragraphs short, aiming for a 6th to 8th grade reading level, writing out acronyms on the first use, and providing both percentages and natural frequencies. It also examines rhetorical moves made in the summaries to address the use of jargon, key term definitions, headings, formatted lists, direct research questions, descriptions of study type, sentence fragments, and the placement of the purpose statement to see how these moves affected the plain language. Although the summaries tended to comply with the paragraph length guidelines, they did not comply with the sentence length, reading level, or acronym guidelines. The variation in compliance could be attributed to researchers' lack of awareness of the guidelines, lack of time to devote to creating brief summaries, or being too immersed in the field to imagine the needs of a lay audience. It could also be attributed to the National Institute of Health not enforcing the guidelines or to researchers not viewing the guidelines as being relevant.

Ensuring the objectivity of systematic reviews and meta-analyses (SRMA) begins with comprehensive searches into diverse resources mining primary studies. Guidelines for systematic reviews recommend authors to routinely search of trial registries to identify unpublished studies. In this dissertation, I investigated the utilization of ClinicalTrials.gov (CTG), the world’s largest clinical trial registry that contains data from clinical trials of products that are subject to United States Food and Drug Administration (FDA) regulation, as an information resource in SRMAs. First, I examined the use of various information resources including CTG in SRMAs published from 2005-2016, and identified the factors associated with their use. Thereafter, to determine the accuracy of trial safety data reported at CTG, I compared the data at CTG with that in corresponding journal articles and FDA drug reviews. I found that trial safety data at both CTG and articles differed frequently from FDA drug reviews, but the differences were modest in magnitude. Finally, I repeated published meta-analysis (conducted using data from primary study articles) with data at CTG to find that most meta-analysis results were reproduced using CTG data. Taken together, this work suggests that CTG should not only be searched more often to find primary research for systematic reviews, but that data at CTG can also be used to conduct quantitative data synthesis.