Table 1.

Comparator group types, associated claims, and considerations.

Categories and definitions	MXRa example	Example claim from a positive randomized controlled trial	Consideration for use in MXR trials
Placebo control: nonspecific elements of the intervention, such as attention or delivery mechanism, without the proposed active elements	Sham virtual reality	The MXR intervention is effective, and this is due to the purported active components	There is a clear set of proposed active components that can be separated from inactive elements Placebo has been tested, and its effects are understood Placebo can be made to appear credible to participants
Specific factors component control: reduced number of active intervention factors (ie, components) in addition to inactive factors	Intervention content delivered in 2D on a tablet	Active components of the intervention benefit from XRb delivery	XR features are likely to boost or underlie effectiveness Some active components (eg, patient education content) can be disentangled from XR delivery
Active comparator: a different, evidence-based treatment	In-person physical therapy, provided by study	XR intervention works better than another specific available treatment	Quality alternatives are available Looking for equivalence (XR is “as good as”) Existing treatment is variable, or there are other benefits of standardizing the comparator
Treatment as usual: continued treatment as is typical for the health condition under study	Instructions to continue current therapy with the personal health care provider	XR intervention works better than typical available treatment in general	Alternatives are available Existing treatments are relatively standardized, or variance can be reduced or accounted for
No treatment control: no intervention elements provided	Providing nothing	XR intervention works better than doing nothing	There are no alternatives available Low potential for placebo effects
Waitlist control: no intervention, but with expectation of future treatment	Provide nothing but promise XR intervention later	XR intervention works better than doing nothing	There are no alternatives available Potential for nocebo (ie, negative expectations for outcomes) if not receiving treatment
No control: treatment group not compared with another group	A single group is assessed before and after use of XR intervention	Outcomes reported to be different after using XR than they were before	Inability to run control group Generally, this method is not acceptable for establishing causal relationships

^aMXR: medical extended reality

^bXR: extended reality