Quality Assessment Tools for Single-Arm Studies: A Rapid Review

OBJECTIVES: Quality assessment (QA) is an important step in the systematic literature review (SLR) process, yet there is currently no validated QA tool for single-arm studies (single-arm trials, open-label extensions, or prospective interventional studies with historical control arms). In rare diseases or for new interventions, single-arm studies may be the main source of evidence available; therefore, an appropriate assessment of their quality and risk of bias is essential. In June 2024, a rapid review was conducted to identify which existing QA tools were utilized in SLRs to assess risk of bias in single-arm studies.

METHODS: Searches were conducted in Embase®, Medline®, and the Cochrane Database of Systematic Reviews. The searches incorporated terms including “single-arm”, ”open-label extension”, ”risk of bias”, ”quality assessment”, and “systematic literature review”. Eligibility screening and data collection were performed by a single reviewer.

RESULTS: Of 894 studies identified for screening (following deduplication), 99 SLRs were included, covering a total of 770 single-arm studies. Most of the included SLRs (88%) were published in the last 5 years (2019–2024). ROBINS-I was the most common QA tool (28%), followed by MINORS (11%), and the Newcastle-Ottawa scale (9%). Quality assessment of single-arm studies was not conducted in 8% of the SLRs, with authors noting an inherent high risk of bias due to the lack of a comparator arm. Additionally, 8% used a bespoke or adapted tool, stating that the available tools were inadequate. The remaining SLRs featured one of fourteen other QA tools.

CONCLUSIONS: This rapid review found that current practice for quality assessing single-arm studies is to use a pre-existing QA tool, a bespoke/adapted tool, or not to conduct QA at all. Currently available tools are insufficiently nuanced to adequately appraise the unique study design of single-arm studies. There is increasing demand for a validated QA tool designed specifically for single-arm studies.