Table A1.

Overview of instruments with justification for inclusion in study.

Instrument	Description	Application in This Study	Justification for Inclusion in P-MIC
Core non-HRQoL Instruments
EQ-HWB-S v1.2	Part of the EuroQol family of instruments, the EQ-HWB-S is a new experimental instrument designed to assess the impact of being a care recipient or caregiver on health and wellbeing [20]. The short version currently has 9 items.	See Figure 1 and Table 1.	Included following advice from consumer advisory group who felt it was important to include a carer. QoL measure due to the strong relationship between child and carer. QoL in children who have chronic conditions. The EQ-HWB-S was chosen because it is a promising new instrument that requires further validation work and is an opportunity to add to the evidence base.
SDQ	The SDQ is a well-validated behavioral screening questionnaire used to assess a child’s emotional and behavioral wellbeing [21,22]. It has 25 items measuring 5 domains [23]. Cut points on each domain can be used to indicate borderline or clinically elevated symptoms. Versions of the SDQ exist for children aged 2–17 years, with self-report available for children aged 11–17 years.	See Figure 1 and Table 1.	Included to capture emotional wellbeing of children to allow the exploration of how HRQoL instruments perform for children with a mental health problem or mental health comorbidity. The SDQ was chosen because it is well validated across a wide age range with cut points to indicate clinically relevant symptoms.
Core HRQoL Instruments
PedsQL Generic Core 4.0	The PedsQL Generic Core 4.0 is a 23 item HRQoL instrument covering 4 domains [24]. Validated version of the PedsQL exist for children aged 2–18 years with self-report available for children ≥8 years [24].	See Figure 1 and Table 1.	Identified as priority for inclusion as it is a generic instrument widely used in pediatric populations with some evidence for performance, but requiring more.
TANDI v2	The TANDI is a new proxy HRQoL instrument developed specifically for children ≤3 years based on the structure of the EQ-5D-Y-3L [25]. It consists of 6 items covering 6 domains [25].	See Figure 1 and Table 1.	Identified as priority for inclusion because it is a promising new instrument for young children requiring further validation work.
EQ-5D-Y (3L and 5L)	The EQ-5D-Y-3L and recently developed EQ-5D-Y-5L, are youth versions adapted from the EQ-5D adult version [26,27]. Both the EQ-5D-Y-3L and EQ-5D-Y-5L are HRQoL instruments consisting of 5 items covering 5 domains. The EQ-5D-Y-3L has 3 severity levels and the 5L has 5. The EQ-5D-Y also includes a Visual Analogue Scale (VAS). Validated versions of the EQ-5D-Y exist for children aged 4–18 years, with self-report from ≥8 years.	See Figure 1 and Table 1.	The EQ-5D-Y-3L was identified as priority for inclusion as it is a generic instrument widely used in pediatric populations with good evidence for performance, but requiring more [13]. The EQ-5D-Y-5L was identified as priority for inclusion because it is a promising new instrument that requires further validation work.
CHU9D	The CHU9D was developed for the purpose of measuring HRQoL in children and young people [28]. It consists of 9 items covering 9 domains. It was initially developed for children aged 7–11 years; however, has been validated in children up to 17 years [29,30]. Additionally, a proxy version of the instrument is being trialed in younger children.	See Figure 1 and Table 1.	Identified as priority for inclusion as it is a generic instrument widely used in pediatric populations with good evidence for performance, but requiring more [13].
Additional HRQoL Instruments
AQoL-6D Adolescent	The AQoL-6D Adolescent was adapted from the AQoL-6D adult version [31]. It is a HRQoL instrument consisting of 20 items covering 6 domains. It was developed with adolescents aged 12–18 years, however, has been used in children aged 11 years [32,33].	See Figure 1 and Table 1.	Although not as widely used as the core instruments in pediatric populations [13], this instrument was identified for inclusion as an additional instrument because of the opportunity to add to the evidence base regarding how this ‘adolescent’ tool might perform in younger children.
HUI2/3	The HUI3 was developed to address issues in the HUI2 and allow for the use of the HUI in both clinical and general populations. It consists of 15 items with between 4 and 6 severity levels. The HUI2 classification system has 7 domains [34] and the HUI3 has 8 [35]. The HUI is officially recommended for use in children ≥5 years, with self-report recommended for children ≥8; however, some studies have used the HUI in children as young as 1 year old [36].	See Figure 1 and Table 1.	This instrument was identified for inclusion because it is a generic instrument widely used in pediatric populations [13]. It was chosen as an additional instrument because the evidence for the psychometric performance of this instrument is more mixed compared with that of core instruments [13].
EQ-5D-5L	The EQ-5D-5L is an adult HRQoL instrument adapted from the EQ-5D-3L [37]. It consists of 5 items with 5 severity levels covering 5 domains. The EQ-5D-5L is recommended to be used in adults and children as young as 16 years.	See Figure 1 and Table 1.	Identified for inclusion as additional instrument because of the opportunity to add to the evidence base regarding how this ‘adult’ tool might perform in younger adolescents.
PROMIS-25 Paediatric Profile	The PROMIS-25 Paediatric Profile is a relatively new HRQoL instrument. It consists of 25 items covering 6 domains [38]. It has child-self report and proxy-report versions available, with child self-report recommended for ≥8 years age and proxy report from ≥5 years.	See Figure 1 and Table 1.	Identified for inclusion as additional instrument because it is a promising new instrument requiring further validation work.
Disease Specific Instruments
PedsQL Asthma Module (Asthma)	The PedsQL Asthma Module is a validated asthma specific pediatric HRQoL instrument [39]. It consists of 28 items (26 items for children aged 2–4 years) covering 4 domains [39]. There are self and proxy report versions for children ≥2 years.	See Figure 1 and Table 1.	The PedsQL Asthma Module was chosen as the disease-specific instrument for the asthma group as it is an asthma specific HRQoL instrument that has previously been validated in children.
KIDSCREEN-27 (ASD)	The KIDSCREEN-27 is a validated generic HRQoL instrument developed for use in children and adolescents and was adapted from the KIDSCREEN-52 [40,41]. It consists of 27 items covering 5 domains. A self-report and proxy version of the KIDSCREEN-27 is available.	See Figure 1 and Table 1.	The KIDSCREEN-27 was chosen as the disease-specific instrument for the ASD group as, although this is a generic HRQoL instrument, it has previously been recommended as a robust HRQoL instrument in children with ASD and no appropriate ASD-specific HRQoL instrument or symptom scale was available [42]. Additionally, a recent literature review found the KIDSCREEN-27 was one of two instruments that aligned with the Convention on the Rights of Persons with a Disability [43].
SDSC (Sleep problems)	The Sleep Disturbance Scale for Children (SDSC) is a validated questionnaire designed to assess sleep-related behaviors in children and adolescents [44]. It consists of 26 items covering 6 domains. Only a proxy report version of the SDSC is available and it was initially validated in children aged 6–16 years; however, another study has successfully utilized the SDSC in children as young as 3 years [45].	As only a proxy report version of the instrument is available, this study will only collect the SDSC via proxy report.	The SDSC was chosen as the disease-specific instrument for the sleep problems group as it is a validated symptom measure in children covering a range of domains and no appropriate sleep-specific HRQoL instrument was available.
CPQ 11-14 (Dental decay)	The Child Perceptions Questionnaire (CPQ) 11-14 is a validated child self-reported oral HRQOL instrument, and is the most commonly used oral HRQoL instrument in children [46,47]. The CPQ 11-14 consists of 16 core items and 2 global items. It was initially designed for children aged 11–14 years; however, recent evidence indicates it may be used in children as young as 5 [48].	As only a self-report version of the 16-item instrument is available, this study will generate a proxy report version to ensure the ability to collect this instrument via proxy report in cases where the child is not able to self-report.	The CPQ 11-14 was chosen as the disease-specific instrument for the dental decay group as it is an oral health-specific HRQoL instrument that has previously been validated in children.
RCADS-25 (Mental health- anxiety and/or depression)	The Revised Children’s Anxiety and Depression Scale (RCADS-25) is a symptom-based scale measuring anxiety and depression in children [49]. It consists of 25 items, 15 related to anxiety and 10 related to depression, covering 6 domains (generalized anxiety disorder, major depressive disorder, obsessive compulsive disorder, panic disorder, separation anxiety disorder and social phobia). The RCADS-25 has been validated in children aged 7–18 years and has both child self-report and proxy report versions available [49].	See Figure 1 and Table 1.	The RCADS-25 was chosen as the disease-specific instrument for the anxiety and/or depression group as it is a validated symptom measure in children covering a range of domains and no appropriate depression- or anxiety-specific HRQoL instrument was available.
SWAN-adapted (ADHD)	The Strengths and Weaknesses of Attention-Deficit/Hyperactivity Disorder Symptoms and Normal Behavior Scale (SWAN) is an ADHD symptom scale that was developed as an adaptation of the Swanson, Nolan and Pelham (SNAP) rating scale [50]. The SWAN is an 18-item proxy-reported measure with 7 severity levels covering 3 symptom areas. The instrument is validated in children aged 6–18 years, but has been used in children as young as 4 [51].	With approval from developer, instrument was adapted slightly to increase readability for lay user. As only a proxy report version of the instrument is available, this study will only collect the SWAN via proxy report.	The SWAN was chosen as the disease-specific instrument for the ADHD group as it is a validated symptom measure in children covering a range of domains and no appropriate ADHD-specific HRQoL instrument was available.