In accordance with PRISMA guidelines, we completed a flowchart detailing the selection process (Figure 1). Following the screening, we included 208 articles for the quality appraisal. From this, 20 articles scored below 51% on the SFS scoring system and were subsequently excluded, leaving a sample of 188 articles. We screened the full text of 188 eligible articles and identified 22 articles which included samples of adolescents living with a CC or disease.
An overview of the study characteristics is presented in Table 2.1 The sample sizes in the studies ranged from 49 - 1,938, and the participants ranged from 8-19 years. More than half of the studies were conducted in developed countries: three in Netherlands, and two each in Canada, United States of America, Australia, and Poland, and one each in France, Taiwan, Spain and Germany.
Most studies (n=18) were published after 2010, with only 4 studies published before 2010. Adolescents with Type 1 Diabetes (n=7) and HIV (n=4) constituted half of the total number of studies. Other conditions were Asthma [34,35], Cerebral Palsy [36,37], Cystic Fibrosis [38,39] and Chronic Pain [40,41] with two studies each; with single studies on Congenital Heart Disease , Sickle cell disease , Cancer , Adolescent Idiopathic Scoliosis , Juvenile Idiopathic Arthritis , Strabismus and Short Stature . Chronic Disease (unspecified by authors) . Additionally, 3 of the studies [34,35,46] used samples of adolescents living with a various chronic illness, rather than looking at adolescents with a specific chronic illness, thereby suggesting that the instruments used in these studies were not symptom/disease specific. All four studies that were conducted in Africa involved ALHIV [47–50] while studies involving adolescents living with type 1 diabetes are mostly from European and American countries [34,35,51–54]. The KIDSCREEN [n=5] and Strengths and Difficulties Questionnaire [n=5] were the most frequently used measuring instruments
Measuring Instruments of Mental health and Mental wellbeing in Adolescents
From the 22 articles, we identified a total of 31 instruments that were used to measure either mental health (n= 8) or mental wellbeing (n= 15) or in combination (n=8) (Table 2.2). We categorised the mental health instruments as those that measure symptoms or aspects related to a specific mental illness (i.e. symptoms of depression), and mental wellbeing instruments as those that measure aspects related to [over-all] mental wellness or positive mental health (i.e. resilience, hopefulness).
Instruments Measuring Mental Health and Mental Wellbeing
Below we discuss the eight instruments measuring both mental health and mental wellbeing.
Health-related quality of life and Quality of life scales
From Table 2, six instruments measure health-related quality of life (HRQoL), namely: Patient-Reported Outcomes Measurement Information System (PROMIS) paediatric profile -25 [34,40,41]; Child Health Questionnaire ; EQ-5D-Y ; Monitoring Individual Needs in Diabetes Youth Questionnaire (MY-Q) ; Quality of Life Profile for Chronic Diseases (PLC) ; and the Short Form 36 Health Survey (SF-36) . HRQoL is a multi-dimensional concept that includes domains related to physical, mental, emotional, and social functioning. It goes beyond direct measures of population health, life expectancy, and causes of death, and focuses on the impact health status has on quality of life . Additionally, the Questions on Life Satisfaction (FLZ) was identified as a QoL measure .
Three studies used the PROMIS instrument [33, 39, 40], which consists of seven subscales in total - of which two measure anxiety and depressive symptoms as mental health domains, and peer relationships as a mental wellbeing domain. The PROMIS instrument is designed to measure HRQoL in both the general population and those living with a CC or illness. Additionally, the PROMIS can be applied widely with both child/adolescent and adult populations. This may allow for comparisons to be made between general child/adolescent populations and those living with a CC.
The other four instruments were only used in one study each. The CHQ consists of 14 subscales: one measuring overall mental health, and seven mental wellbeing domains such as role/social physical functioning, role/social emotional functioning, role/social behavioural functioning, parent impact-emotion, self-esteem, behaviour and family cohesion. The CHQ is the only instrument in this category that is age specific that can be used with general child/adolescent populations and those living with a chronic disease/disorder. Therefore, like the PROMIS instrument, the CHQ can be used to make comparisons between these populations.
The EQ-5D-Y is a child and adolescent friendly version of the EQ-5D HRQoL instrument. It has five subscales in total; three of which measure mental wellbeing - looking after myself, doing usual activities and one which measures mental health - feeling worried, sad or unhappy.
MY-Q instrument has been developed to measure HRQoL in adolescents with diabetes. The MY-Q consists of four subscales in total, one mental health domain namely worries and three mental wellbeing domains namely, general quality of life, the teenager’s social life and emotional wellbeing.
PLC was originally developed in Germany to measure HRQoL in chronic patients, regardless of age. It consists of four mental wellbeing domains - positive mood, ability to relax and enjoy, sense of belonging to others and capacity - and one mental health (negative mood) subscale(s).
SF-36 consists of 8 subscales; three which measure mental health - limitations in social activities because of emotional problems, psychological distress & limitations in usual role activities due to emotional problems - and one which measure mental wellbeing - general mental health and wellbeing.
Like the PLC, the Questions on Life Satisfaction (FLZ)  was also developed in Germany as a generic measure of subjective QoL. The instrument consists of 16 subscales, 5 of which are aimed at measuring mental wellbeing (friends, family life, partner relationship/sexuality, ability to relax, independence from help) and 1 is aimed at measuring mental health (freedom from anxiety).
Disease specific instrument
The other instrument included in this category, The Diabetes Stress Questionnaire  is a measure of diabetes stressors that consists of 8 subscales, three which measure mental health - distress-worry, peer stress & adverse personal effects and one which measures mental wellbeing -self-care. Like the MY-Q, it was specifically developed for adolescents living with diabetes.
Instruments Measuring Mental Wellbeing
As previously mentioned, instruments measuring mental wellbeing were categorised as those who measure positive aspects of mental health and mental wellness. Below we briefly describe these instruments. As seen below, we found that the HRQoL instruments were common mental wellbeing measures. The other instruments in this category were described as those measuring aspects or constructs related to mental wellbeing (i.e. measures of resilience or self-concept).
Health related quality of life and quality of life scales
As seen in Table 2, six of the 15 mental wellbeing measures are aimed at measuring HRQoL. These are the Paediatric Quality of Life Inventory (PedsQL) [36,41,52], The KIDSREEN questionnaires [36,45,54,57,58], Cystic Fibrosis Questionnaire (CFQ)  and the Vécu et Santé Perçue des Adolescents (VSP-A) .
The PedsQL was used in three of the 22 included studies. It is a generic HRQoL instrument used with children and adolescent populations. It consists of four subscales, two of which are categorised as mental wellbeing scales – emotional functioning and social functioning.
The KIDSCREEN-27 was developed to measure HRQoL in children and adolescents. It has five subscales, three of which measure mental wellbeing namely, psychological wellbeing, autonomy & parents, and peers & social. The KIDSCREEN was further developed into a longer version – KIDSCREEN-52 that consist of 10 subscales, with seven of these aimed at measuring mental wellbeing such as, psychological wellbeing, moods and emotions, self-perception, autonomy, parent relations and home life, social support and peers and acceptance(bullying). Additionally, the KIDSCREEN-10 is the shorted version of the original instrument which represents a unidimensional construct of HRQoL.
The CFQ is a disease specific instrument aimed at measuring HRQoL in patients with cystic fibrosis. It has five domains in total and three mental wellbeing domains- energy/wellbeing, social limitations and emotional state.
The VSP-A is a generic HRQoL instrument for adolescence that was originally developed in France. The instrument has 10 subscales in total and seven mental wellbeing subscales- psychological wellbeing, relationships with friends, relationships with parents, leisure activities, relationships with teachers, relationships with medical staff and body image
Additionally, three of the instruments were identified as QoL instruments namely, WHO Quality of Life BREF ; Cerebral Palsy Quality of Life Questionnaire-Teen [36,57]; and the Quality of Life in Short Stature Youth (QoLiSSY) .
The WHO Quality of Life BREF is a generic measure of QoL that has 4 subscales, two of which measure mental wellbeing- psychological health and social relationships.
Cerebral Palsy Quality of Life Questionnaire-Teen is a disease and age specific instrument aimed at measuring the QoL of adolescents living with cerebral palsy. The instrument has eight subscales, five of which measure mental wellbeing- social wellbeing, emotional wellbeing, participation and communication and school wellbeing.
QoLiSSY is another disease and age specific questionnaire aimed at measuring QoL in youth diagnosed with short stature. The questionnaire has six domains, with three of those measuring mental wellbeing- social, emotional, coping, beliefs.
Instruments measuring constructs of mental wellbeing
Five of the mental wellbeing instruments are aimed at measuring various constructs related to mental wellbeing. These are WHO-5 Wellbeing Index [51,52]; Child Youth Resilience Measurement (CYRM-28) ; Hunter Opinions and Personal Expectations scale (HOPES) ; Tennessee Self-Concept scale ; and the FACIT-Sp-12 Spiritual Wellbeing scale . All these instruments were used in one study each.
WHO-5 Wellbeing Index is a short self-report measure of current psychological/mental wellbeing in any population. It consists of 5 items which represent a unidimensional construct of mental wellbeing.
CYRM-28 is used to measure resilience among youth aged 9-23 years. It has four subscales: individual, relational, community and cultural. These subscales are aimed at screening and measuring resources available to the individual which may support and strengthen their resilience. The HOPES measures hope and despair in adolescent and adult populations. It has three subscales: hope, despair and global personal happiness. Tennessee Self-Concept measures the following six dimensions of self-concept, namely: physical, moral, personal, family, social and academic. It can be used with adult and child/adolescent populations.
FACIT-Sp-12 Spiritual Wellbeing scale was originally developed based on the experiences of cancer patients, but has since been validated to be used to assess spirituality and spiritual wellbeing in adolescents living with chronic or life threatening conditions. It consists of four domains- spiritual wellbeing, meaning, peach and faith. It is the only instrument in this category which is specifically aimed at adolescents with CCs.
Instrument measuring healthcare needs in youth
The Healthcare Needs Scale for youth with Congenital Heart Disease HNS-CHD  is a disease specific instrument which assesses the transitional healthcare needs of adolescents and young adults living with a congenital heart disease. Two of the five subscales measure individual and interpersonal and policy needs which are related to the patient’s mental wellbeing.
Instruments Measuring Mental Health
Below we briefly discuss the mental health measures included in this study. Unlike the previous two categories, the mental health measures only include one measure of HRQoL. The other instruments are categorised as measuring symptoms of mental health such as anxiety or depression. Additionally, one measure was identified as measuring the healthcare needs of adolescents.
Instruments measuring symptoms of mental health
Six of the instruments included are aimed at measuring symptoms of mental health or screening for emotional and behavioural problems. These are the Strength and Difficulties Questionnaire (SDQ) [43,44,49,54,57]; Child Depression Inventory instruments (CDI & CDI-short form) [47,48]; Center for Epidemiological Studies Depression (CES-D) ; and the Revised Children’s Manifest Anxiety Scale  and the Beck Hopelessness scale .
SDQ is aimed at screening emotional and behavioural problems in children and adolescents. It consists of 5 mental health subscales namely: emotional symptoms, conduct problems, hyperactivity/inattention, peer relationships problem and prosocial behaviour. The SDQ was used in 5 out of the 22 studies.
CDI focuses on measuring symptoms of depression in children and adolescents. It has five mental health subscales: anhedonia, negative mood/physical symptoms, negative self-esteem, interpersonal problems, and ineffectiveness. The CDI is also available in a shorter form, CDI-Short Form, which consists of four subscales namely: negative mood/physical symptoms, negative self-esteem, interpersonal problems and ineffectiveness. Therefore, the anhedonia subscale is dropped in the shorter form. The CDI and CDI-Short Form were used in one study each.
The following instruments were used in one study each. CESD is used to measure and screen for symptoms of depression. It can be used in the general population and those living with a CC. The CESD consists of four subscales namely, depressive affect, somatic complaints, positive affect and interpersonal activity. Revised Children’s Manifest Anxiety Scale is used to measure symptoms of anxiety in adolescents and children. It has three subscales namely, psychological anxiety, worry/oversensitivity and social concerns/concentration. The Beck Hopelessness scale is used to measure hopelessness or negative feeling about the future in child/adolescent and adult populations. It consists of 3 subscales related to hopelessness: feelings about the future, loss of motivation and expectations.
Instruments measuring health related quality of life and healthcare needs
One of the mental health instruments was aimed at measuring HRQoL. Like the aforementioned PedsQL, the Paediatric Quality of Life Inventory Diabetes Module (PedsQL-DMTM) measures HRQOL in children and adolescents living with diabetes. The instrument consists of 4 subscales, one of which measures mental health namely, worry and communication.
The questionnaire on health needs for adolescents  is aimed at measuring the healthcare needs of adolescents. It was used to establish the concurrent validity of the HNS-CHD. It consists of 5 subscales, three of which can be described as measuring mental health namely, mental health, interpersonal concerns and behavioural concerns.
Physical Wellbeing Subscales
We found that 21 of the instruments included one or more subscales related to physical wellbeing. As shown in Table 2, some of the physical wellbeing subscales may overlap with the mental health and mental wellbeing subscales. For example, the Center for Epidemiological Studies Depression (CESD) questionnaire includes 4 subscales aimed at measuring symptoms of depression. One of the subscales, ‘somatic complaints’ relates to physical symptoms of depression. However, it is also relates to the individuals physical wellbeing. Similarly, the Short Form Health 36 Survey (SF-36) includes subscales like ‘Limitations in social activities because of physical or emotional problems’, which again relates to both physical wellbeing and mental health (i.e., emotional state has a negative effect on functioning). This is not surprising as mental health, as it relates to mental illness considers somatic symptoms or functioning capabilities as an indicator to diagnose and assess the severity of an individual’s mental illness.