Table 1.

Criteria for the inclusion of studies in the meta-analysis

PICO Field	Criteria
Population	Included participants were children and adolescents aged ≤ 18. 18-year-olds were included on the basis that previous meta-analyses (Romero-Ayuso et al. 2021), scoping reviews (Adabla et al. 2021), and global prevalence reviews (Faraone et al. 2021) investigating children with ADHD have included 18-year-olds. Studies where participants had a formal diagnosis of ADHD according to the International Classification of Diseases 10th Revision (ICD-10) (WHO 2001), the DSM-5 (APA 2013), or any of their previous iterations were included. Participants who did not have a formal ADHD diagnosis, but displayed ADHD-like symptoms (i.e. inattention, hyperactivity) as observed by an external party (e.g., clinician, research personnel), or as assessed by a validated measure were also included. Excluding participants based on an absence of formal diagnosis was deemed inappropriate given that access to ADHD diagnostic services is reported to be difficult for caregivers of children with attention and/or hyperactivity problems (Fridman et al. 2017). As such an absence of a formal diagnosis does not mean the participants do not have ADHD, rather they may lack access to diagnostic services
Intervention	Any immersive VR-based intervention was included where the participant’s outward environment is occluded using a head-mounted display (HMD) or the integration of two or more computers (body-tracking sensors or specialised interface devices with 3D graphics). Non-immersive interventions where the content was delivered on a flat-screen monitor with no occlusion of the user’s outward environment were excluded
Comparator	Studies using no treatment/waiting list, where participants received no intervention were included under the term of passive control groups. Wait-list control groups were included under the umbrella term of passive control groups as participants are withheld treatment and are offered treatment at the end of the study (e.g. Bahar‐Fuchs et al. 2019). Studies using an active comparator group, where participants received an intervention with similar levels of contact with research personnel and a similar number of sessions as the intervention group (e.g. psychotherapy or non-immersive VR) were included. Also, as per clinical guidelines, medication was also considered as an active comparator group
Outcome	Included studies used standardised outcome measures assessing either global cognitive functioning or any specific domain of cognitive functioning. Examples of eligible outcome measures include any Continuous Performance Test (CPT) (e.g. Tests of Variable Attention [TOVA], or the Integrated Visual and Auditory CPT [IVA]), or any subset of the Wechsler Intelligence Scale for Children-IV [WISC-IV] (e.g. Working Memory Index [WMI])