Parallel RCT Design

A randomised control trial design in which participants are randomly assigned to either two or more treatment arms to determine superiority, equivalence or non-inferiority.

The simplest and most common Randomised Control Trial design. In this design, participants, once enrolled, are randomly assigned to either a treatment or comparator research group. Participants in either group are then compared using a primary outcome measure to determine whether the intervention has met the aims of the study or not.

A matched paired parallel design ensures that each participant in a treatment group is matched to another participant in the control group based on specific criteria. These criteria are often control variables associated with the primary outcome measure. This variation upon the standard parallel arm design can be helpful when controlling for other factors, however, it can also be slower to recruit participants meeting specific matching inclusion criteria.

Parallel arm designs can also be expanded to included multiple treatments. This variation is called a multi-arm parallel design. This type of design is attractive when multiple novel treatments are being compared simultaneously against a single control group and when time to trial completion is an important consideration. However, this style of design cannot allow for interaction effects between treatments.

Advantages of this research design are that it is simple, versatile and generally accepted. By including more participants, the results obtained from this type of research design are often considered more valid and simpler to analyse. This type of research design is also not prone to the concerns of other designs such as carryover effects and washout periods. However, this type of research design may require a larger sample size and incur greater financial costs.

This type of research design is well suited to demonstrating superiority, equivalence or non-inferiority, particularly when investigating acute conditions.

• Parallel Group Designs https://www.mussenhealth.us/clinical-trials-2/parallel-group-designs.html
• Reda DJ. Overview of the Randomized Clinical Trial and the Parallel Group Design. Cham: Springer International Publishing; 2017. p. 51-58.
• Dalton B, Bartholdy S, McClelland J et al. Randomised controlled feasibility trial of real versus sham repetitive transcranial magnetic stimulation treatment in adults with severe and enduring anorexia nervosa: the TIARA study. BMJ open. 2018;8:e021531. 10.1136/bmjopen-2018-021531
• Haun MW, Tönnies J, Krisam R et al. Mental health specialist video consultations versus treatment as usual in patients with depression or anxiety disorders in primary care: study protocol for an individually randomised superiority trial (the PROVIDE-C trial). Trials. 2021;22:327. 10.1186/s13063-021-05289-3