What’s the difference between an n-of-1 trial and a parallel random control trial (RTC)?

Treatments⁠—both pharmaceutical and nonpharmaceutical⁠—are classically evaluated in random control trials (RTCs). Large, carefully selected groups of participants and their doctors are blinded to which patients are getting which treatment or control.

In contrast, an n-of-1 trial looks only at the effects of different treatments on a single person. The trial periods and target outcomes are defined ahead of time. With the assistance of a compounding pharmacists, blinding and placebos are possible.

The two types of trials have radically different purposes⁠—the RTC is to determine broad efficacy and average treatment effects, and the n-of-1 determines the effect on a single individual.

“All RCTs do is show that what you’re dealing with is not snake oil,” according to William R. Shadish, PhD, a professor of psychological science at the University of California at Merced. “They don’t tell you the critical information you need, which is which patients are going to benefit from the treatment.”

According to Dr. Sunita Vohra and Salima Punja, BSc:

results from randomized controlled trials (RCTs), often considered the ‘gold standard’ of research evidence, are often not well suited to the realities of clinical practice given patient heterogeneity, comorbidities, and the use of multiple concurrent therapies. In fact, RCTs may exclude the majority of patients seen in routine clinical practice. In addition, evidence is lacking on the long-term effectiveness, comparative effectiveness, and additive effectiveness of many therapies for chronic conditions. This lack of relevant evidence can limit a clinician’s ability to make evidence-based decisions.

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