A '''single-arm study design''' is a type of clinical or experimental study where all participants receive the same intervention, with no control or placebo group.<ref name=":0">{{Cite journal |last=Wang |first=Minyan |last2=Ma |first2=Huan |last3=Shi |first3=Yun |last4=Ni |first4=Haojie |last5=Qin |first5=Chu |last6=Ji |first6=Conghua |date=2025 |title=Single-arm clinical trials: design, ethics, principles |url=https://spcare.bmj.com/lookup/doi/10.1136/spcare-2024-004984 |journal=BMJ Supportive & Palliative Care |language=en |volume=15 |issue=1 |pages=46–54 |doi=10.1136/spcare-2024-004984 |issn=2045-435X |pmc=11874317 |pmid=38834238}}</ref> The term "single-arm" refers to the presence of only one participant group, in contrast to designs such as randomized controlled trials, which include both a treatment arm and control or placebo arm.<ref name=":0" />
== Overview == Single-arm trials include one experimental group without the inclusion of a parallel control group. The design is open-label and does not involve randomization or blinding.<ref name=":0" /> This type of study design is commonly applied to advance stage cancer, rare diseases, emerging infectious diseases, new treatment methods, and medical devices.<ref name=":0" />
While randomized control trials are considered the “gold standard” in clinical research, they are not always feasible due to limitations in the study population, challenges in obtaining evidence, high costs, and ethical considerations.<ref name=":0" /> As a result, single arm trials are used to address these concerns.
== Applications == Since there is no randomization in single-arm trials, all patients receive the same intervention within a particular study/trial.<ref name=":0" /><ref name=":1">{{Cite journal |last=Yao |first=Shuna |last2=Shang |first2=Qingyao |last3=Ouyang |first3=Meishuo |last4=Zhou |first4=Heng |last5=Yao |first5=Zhihua |last6=Liu |first6=Yanyan |last7=Luo |first7=Sheng |date=2025 |title=Designing Single-Arm Clinical Trials: Principles, Applications, and Methodological Considerations |url=https://www.jstage.jst.go.jp/article/ace/7/3/7_25011/_article |journal=Annals of Clinical Epidemiology |volume=7 |issue=3 |pages=90–98 |doi=10.37737/ace.25011 |pmc=12279405 |pmid=40697795}}</ref> This design is most commonly used in early-phase clinical trials or in studies of rare or serious diseases, where including a control group may be impractical or unethical.<ref name=":0" /><ref name=":1" />
* Phase I studies primarily assess safety, tolerability, and pharmacokinetics over a relatively short duration. They are used to inform dose selection for subsequent studies.<ref name=":1" />
* Phase II studies primarily assess preliminary efficacy over a longer duration (months to years). They are used to support proof-of-concept assessments.<ref name=":1" />
== Interpreting results == With the absence of a control group, effectiveness is measured against an external standard. This can include benchmarks established from previous studies or historical control data, and are used to define minimum efficacy thresholds and expected performance ranges.<ref name=":1" /><ref name=":2">{{Cite journal |last=Seymour |first=Lesley |last2=Ivy |first2=S. Percy |last3=Sargent |first3=Daniel |last4=Spriggs |first4=David |last5=Baker |first5=Laurence |last6=Rubinstein |first6=Larry |last7=Ratain |first7=Mark J. |last8=Le Blanc |first8=Michael |last9=Stewart |first9=David |last10=Crowley |first10=John |last11=Groshen |first11=Susan |last12=Humphrey |first12=Jeffrey S. |last13=West |first13=Pamela |last14=Berry |first14=Donald |date=2010-03-15 |title=The Design of Phase II Clinical Trials Testing Cancer Therapeutics: Consensus Recommendations from the Clinical Trial Design Task Force of the National Cancer Institute Investigational Drug Steering Committee |url=https://aacrjournals.org/clincancerres/article/16/6/1764/76067/The-Design-of-Phase-II-Clinical-Trials-Testing |journal=Clinical Cancer Research |language=en |volume=16 |issue=6 |pages=1764–1769 |doi=10.1158/1078-0432.CCR-09-3287 |issn=1078-0432 |pmc=2840069 |pmid=20215557}}</ref>
In oncology, time-to-event outcomes such as progression-free survival and overall survival may be used to assess treatment effects.<ref name=":2" />
== Bias and limitations == Without a control group or randomization there are several sources of bias.<ref name=":0" /> Differences in patient selection, baseline characteristics, and clinical management may affect observed outcomes.<ref name=":0" /> Confounding variables cannot be fully controlled, and causal relationships cannot be established with certainty.
==References== {{reflist}}
{{Medical research studies}} {{Experimental design}} {{Statistics|applications|<!-- collection| -->state=collapsed}} {{Public health}}
Category:Clinical research Category:Epidemiological study projects Category:Evidence-based practices Category:Design of experiments Category:Causal inference Category:Experiments Category:Research methods