Main findings
Children with borderline or clinical levels of mental health symptoms each had lower ratings of HRQoL than those with physical health problems, whilst children with physical–mental multimorbidity showed even lower ratings over-and-above the additive effect of both problems. Mental health problems were associated with poorer HRQoL for older compared to younger children, though were still associated with a significant and clinically meaningful difference in children aged 4–7 years. In subgroup analyses, the interaction effect was significant for boys only, meaning that boys with physical–mental multimorbidity are at particular risk of disproportionately poorer HRQoL than boys with either mental or physical health problems alone.
In line with previous research we found children with clinical levels of mental health symptoms have poorer HRQoL than children with physical health problems [
9,
12‐
14], and that greater mental health problems are associated with poorer HRQoL [
18‐
20]. Our study provides novel evidence that quantifies the relative relationships between HRQoL and borderline mental health symptoms versus physical health problems, and showed that borderline mental health symptoms are also associated with a clinically important difference in children’s HRQoL that is larger than that of physical health problems. This is important in determining groups of children in greater need for support.
Our finding that mental health problems were associated with lower ratings of HRQoL in older compared to younger children has been noted previously for children with depression (as rated by their parents) [
13], though we extended this knowledge to include borderline symptoms. This finding may be due to greater disease severity [
14] or greater psychiatric comorbidities [
13] in adolescents. Yet others have noted no difference by child age [
9,
40]. Longitudinal studies examining the onset and progression of mental health problems are warranted to disentangle these mixed findings.
Our study extends a previous finding [
12] of a significant interaction effect in children with physical–mental multimorbidity by examining a larger multimorbid sample across a broader range of mental health symptoms, and adjusting for more child, parent, family and social factors. Whilst we found a significant interaction effect, as per Sawyer et al. [
12], our analyses revealed that this does not extend to borderline mental health symptoms, possibly due to the smaller span of scores within the borderline range compared with the clinical range of symptoms.
Our finding that the interaction effect of physical–mental multimorbidity was significant for boys but not girls is novel. This difference may arise due to our finding that the associations between physical and mental health problems and HRQoL were each larger and more significant for girls than boys; i.e. girls with physical health problems show significantly lower ratings of HRQoL compared to their healthy peers (regardless of their mental health status), however, for boys this was only true if they
also had mental health problems. The differing relationships observed by sex may also relate to the type of mental health problems experienced by boys and girls, with internalising problems previously found to be related to poorer HRQoL in girls and externalising problems more-so for boys [
20]. This warrants further exploration in the context of the interaction of physical–mental multimorbidity, to determine whether a particular combination of problems accounts for this difference.
Our sensitivity analysis found no interaction effect when using child self-reported HRQoL, which may be related to a number of factors. Firstly, parent ratings of children’s HRQoL tend to be lower than the child’s self-report when the child has chronic health conditions [
8,
14,
40,
41], which may overestimate the deficit in HRQoL and lead to a stronger interaction effect of having multiple chronic conditions by parent-report. Secondly, in the current study, children and parents rated HRQoL using different measures. Whilst the PedsQL and CHU9D are moderately correlated (
r = 0.63; when children self-report on both measures [
42]), the use of different measures that comprise different domains of HRQoL, with different respondents makes it difficult to compare the findings. Similarly, the higher degree of variance in HRQoL scores that is explained using parent-report would likely be related to having the same respondent (parents) rate both the predictor (child’s health status) and outcome (HRQoL); i.e. part of this observed relationship reflects the parent’s underlying perception of the child’s health and wellbeing. Parent’s perception of their child’s health status can be further augmented by parents’ own mental health problems [
43], which may also lead to the observed differences in child versus parent-report of HRQoL.
The overlap between measures of mental health and HRQoL is important to consider when assessing associations between the two [
10,
37], though many studies have not addressed this [
36]. Our finding that mental health problems were associated with larger differences in psychosocial domains of HRQoL is in line with a previous systematic review [
11], however, this differs from others that have found stronger relationships in school functioning domains [
14,
44]. Importantly, the relationship between mental health and HRQoL extended beyond the expected emotional health domain into all other domains examined. This broad relationship has previously been noted in studies using the PedsQL [
9,
44], but is less consistently found using other measures [
12‐
14]. Our findings add to a growing literature that mental health and HRQoL are related but distinct concepts [
8].
In our adjusted model, only parental mental illness was associated with a clinically meaningful difference in the child’s HRQoL, holding all other factors constant. As the respondent in our study was the child’s mother in 98% of instances, our findings are similar to previous work by Bastiaansen et al. [
20], which found that mother’s psychopathology was individually associated with poorer child HRQoL, though this was no longer significant in their final adjusted model. In contrast, recent evidence suggests parental mental illness may only be related to poorer HRQoL in the domain of autonomy & parent relation for adolescent girls, and may not be associated with any deficits in HRQoL for adolescent boys [
45]. Whilst parental mental health may be an important, potentially modifiable, focus for intervention that may improve children’s HRQoL [
20], further exploration is warranted particularly regarding the persistence of parental mental illness and links to children’s mental health problems as well as the implications for child self-report and parent-report of the child’s HRQoL over time.
Strengths, limitations and recommendations for future research
This study presents the first evidence of the relative relationships between physical health, borderline and clinical levels of mental health symptoms and children’s HRQoL in a large, population-based sample. Using a population sample enabled us to detect a greater number of children within the borderline mental health range than might be possible with a clinical sample. The size of the sample enabled us to examine relationships within smaller subgroups of children, and relationships with a range of child, parent, family and social factors that have not been previously examined in this context.
Limitations include the use of parent-reported data on children’s physical and mental health problems rather than diagnosed conditions; in the absence of a gold-standard diagnostic interview, and the inconsistent availability of parent-reported mental health conditions across waves, we used the SDQ as a validated tool available at every time point. We recognise that use of the SDQ to measure mental health problems means not all children who screen positive for mental health problems would meet clinical criteria for a psychiatric diagnosis and, vice versa [
46], some children with diagnosed conditions may be well-managed with treatment and may have low scores on the SDQ. This misalignment in identifying children with mental health problems can be seen within the current study regarding the differing results between SDQ and parent-report of children’s mental health diagnoses and speaks to the wider difficulty in accurately identifying this population. On the other hand, a strength of using the SDQ for all children meant we could identify children with borderline symptoms that may have gone undetected using formal clinical criteria. Using the same respondent for child mental health and HRQoL is a limitation which we have made efforts to address by including a range of parent factors as covariates in adjusted analyses, and conducted a sensitivity analysis using child self-reported HRQoL. An additional limitation arises from the pooled cross-sectional design of the study, such that we cannot comment on the direction of effect, and the analysis cannot control for unobserved factors (e.g. parent factors) that may impact reports of child HRQoL and child health. Whilst it seems likely that physical health problems would cause poorer HRQoL, it is not necessarily the case that the relationship between mental health problems and HRQoL is unidirectional. A longitudinal analysis is planned to examine this interplay of symptoms, as well as the potentially changing influence of child, parent, family and social factors, on children’s HRQoL throughout childhood and adolescence.