Background
Sound reading and writing skills are essential factors in order to obtain labour market success [
1,
2] and thereby a good and healthy life [
3]. Thus, already in childhood and adolescence, the possibility of achieving a successful and healthy life is being founded [
4]. Reading and writing skills may open up opportunities in life which may be the foundation of a good health presently and in the future as adolescents and adults [
1]. Assessing overall perception of adolescents’ own health status, is commonly done using a single item asking about their self-rated health [
5,
6], and studies have shown that it strongly predicts outcomes such as morbidity and mortality [
7,
8].
Overall, boys tend to have a slightly better self-rated health than girls [
7,
9]. For both genders in adolescence, self-rated health seems to a large extent to be based upon mental health [
10], which may explain the negative association between perceived stress in adolescence and mental- and physical health [
11]. Studies also point to the fact that loneliness through adolescence increases the risk for poor self-rated health, psychological and physical health in adolescence and into adulthood [
12,
13]. Besides, self-rated health has also been associated with physical, personal and behavioural factors [
9]; for instance a poor self-rated health among adolescents has shown to be predictive of different markers of biological dysregulation in early adulthood [
14]. Socioeconomic status (SES) seems also to be predictive of self-rated health among adolescents, and negative life events during childhood have been shown to be predictive of different depressive problems [
7,
9,
15,
16]. Another essential factor affecting adult self-rated health is education, thus low education increases the risk of low self-rated health [
17,
18]. Education is in most cases a prerequisite for future employment and income, which are some of the basic factors in a good and healthy life [
3,
19,
20]. For that reason, education is a social determinant of health, and low education contributes to increased inequality in health [
4].
Reading and writing difficulties (RWD) may lead to low education, and thereby low income in adulthood [
1,
2,
21,
22]. RWD cover a wide spectrum of different difficulties whereas dyslexia is the predominant cause [
23]. It is estimated that between 5 and 22.5% of children and adolescents suffer from RWD, depending on the population under investigation [
24‐
26]. In a Danish context the Danish Health Authority estimates the prevalence of dyslexia to be between 7 and 20% [
27,
28], whereas the prevalence of RWD is expected to be even higher. Besides being strongly correlated with educational attainment, RWD are also associated with a number of negative factors, such as ADHD [
29], criminal conduct [
30] and an increased risk of internalizing, anxiety and depressive symptoms [
31].
Based on these negative associations, it seems plausible that RWD independently may be associated with poor self-rated health. If in fact the association between RWD and self-rated health is already present in adolescence, this is an inequality in itself, and it reaches far beyond health inequality in adolescence.
Functional literacy and numeracy have been shown to be associated with self-assessed health in an adult population [
32]. In addition, a pattern with poor health-related outcomes among adults having RWD was shown [
31,
33‐
37], although one study did not find this association to be statistically significant [
37]. Amongst adults, it has been shown that different types of RWD are associated with health-related quality-of-life (HRQoL) [
38,
39]. As with adults, it seems that RWD among children and adolescents are risk factors for different emotional and mental problems such as low self-esteem, anxiety and unhappiness [
31,
40]. Arkkila et al. found poor mental outcomes to be more pronounced among adolescents with specific language impairment compared to adolescents without it. Despite that, they found no difference in HRQoL between the two groups when measuring with the 16D-questionnaire validated for use among adolescents [
41]. However, several other studies found that poor mental health status explained differences in HRQoL none of them being measured with the SF-36 instrument, though [
42‐
45]. The current scientific literature does show a pattern where RWD is associated with poor health-related outcomes, even though no studies to our knowledge have investigated the relationship between RWD and self-rated health measured by the SF-36 among adolescents.
Thus, the overall purpose of this study was to investigate the association between RWD and self-rated health among adolescents. Since adolescents to a high degree may base their self-rated health on their mental health, the purpose was moreover to investigate how loneliness and perceived stress, as indicators for mental health, mediate the association between RWD and self-rated health, thereby identifying significant possible risk factors for future prospective studies.
Statistics
Descriptive statistics on covariates was applied, stratified on the RWD and non-RWD groups. Chi2-test or t-test for categorical and continuous variables, respectively was performed.
In order to qualify the discussion of potential sources of selection bias, non-response analyses were conducted. Chi2-test was used to test for differences between gender and self-assessed SES.
A logistic regression model was used to analyse the association between RWD and self-rated health. Three models were applied: Model 1 investigated the crude association; Model 2 investigated how loneliness and perceived stress, as indicators for mental health, mediated the association between RWD and self-rated health; Model 3 was a repetition of Model 2 with further adjustments by the addition of gender, age, self-assessed SES and negative childhood events. All analyses were adjusted for cluster on school-level using the “cluster” option in the STATA procedure “logistic”, which ensures robust Standard Errors despite the cluster effect. Results were reported as odds ratios (OR) with corresponding 95% confidence intervals (CI).
The software package STATA version 15.1 was used for the analyses.
Ethics
The FOCA cohort was approved by the Danish Data Protection Agency (no. 1–16–02-461-16). The pupils gained access to the questionnaire through their UNI-login, a personal login given to all pupils in Denmark. It was voluntary for the adolescents to answer the questionnaire, and they had the right to withdraw their undertaking of participation at any time. All the answers were treated strictly confidential, and the adolescents were guaranteed full anonymity.
Results
Distribution of self-rated health and baseline characteristics of the study population are presented in Table
1. The baseline characteristics were significantly different between the RWD and non-RWD groups except for gender (Table
1). Self-rated health was lower among pupils having RWD compared to pupils without RWD (
p < 0.001).
Table 1
Characteristics of the study population
Self-rated health | | | | < 0.001b* |
Low (%) | 2606 (26.7) | 338 (35.5) | 2268 (25.8) | |
High (%) | 6386 (65.5) | 494 (51.8) | 5892 (67.0) | |
Missing (%) | 756 (7.8) | 121 (12.7) | 635 (7.2) | |
Gender | | | | 0.055 b |
Female (%) | 4973 (51.0) | 458 (48.1) | 4515 (51.3) | |
Male (%) | 4775 (49.0) | 495 (51.9) | 4280 (48.7) | |
Alder, mean (SD) | 15.8 (0.4) | 16.0 (0.5) | 15.8 (0.4) | < 0.001c* |
Self-assessed SES | | | | < 0.001b* |
Low (%) | 233 (2.4) | 49 (5.1) | 184 (2.1) | |
Medium (%) | 5411 (55.5) | 552 (57.9) | 4859 (55.3) | |
High (%) | 3529 (36.2) | 248 (26.0) | 3281 (37.3) | |
Missing (%) | 575 (5.9) | 104 (10.9) | 471 (5.4) | |
Negative childhood events | | | | < 0.001b* |
0 events (%) | 940 (9.6) | 84 (8.8) | 856 (9.7) | |
1–3 events (%) | 5769 (59.2) | 433 (45.4) | 5336 (60.7) | |
4–7 events (%) | 1616 (16.6) | 181 (19.0) | 1435 (16.3) | |
8–11 events (%) | 234 (2.4) | 56 (5.9) | 178 (2.0) | |
Missing (%) | 1189 (12.2) | 199 (20.9) | 990 (11.3) | |
Loneliness | | | | < 0.001b* |
Not lonely (%) | 7358 (75.5) | 609 (63.9) | 6749 (76.7) | |
Lonely (%) | 2379 (24.4) | 341 (35.8) | 2038 (23.2) | |
Missing (%) | 11 (0.1) | 3 (0.3) | 8 (0.1) | |
Perceived stress a, mean (SD) | 14.3 (6.4) | 16.5 (6.1) | 14.1 (6.4) | < 0.001c* |
Characteristics of the respondents, who did or did not answer the item concerning RWD are shown in Table
2. More boys (57.1%) than girls (42.9%) did not answer the RWD item (
p < 0.001). No differences in self-assessed SES were observed.
Table 2
Non-response analyses in relation to the RWD question
Gender | | | | 0.001a* |
Female (%) | 5167 (50.7) | 4973 (51.0) | 194 (42.9) | |
Male (%) | 5033 (49.3) | 4775 (49.0) | 258 (57.1) | |
Self-assessed SES | | | | 0.916a |
Low SES (%) | 241 (2.4) | 233 (2.4) | 8 (1.8) | |
Medium SES (%) | 5574 (54.7) | 5411 (55.5) | 163 (36.1) | |
High SES (%) | 3633 (35.6) | 3529 (36.2) | 104 (23.0) | |
Missing (%) | 752 (7.4) | 575 (5.9) | 177 (39.2) | |
The association between RWD and self-rated health is shown in Table
3. RWD and self-rated health were significantly associated in all three models (Table
3). Adjustments for loneliness and perceived stress in Model 2 led to a reduction of the association between RWD and low self-rated health from 1.77 (95% CI: 1.51–2.09) in Model 1 to 1.47 (95% CI: 1.23–1.74) in Model 2. In the fully adjusted Model 3 the OR was 1.37 (1.14–1.66).
Table 3
Crude and adjusted OR (95% CI) for poor self-rated health
RWD |
No | 1 | | 1 | | 1 | |
Yes | 1.77** | 1.51–2.09 | 1.47** | 1.23–1.74 | 1.37* | 1.14–1.66 |
Loneliness |
Not lonely | | | 1 | | 1 | |
Lonely | | | 1.53** | 1.37–1.71 | 1.51** | 1.34–1.69 |
Perceived stress | | | 1.11** | 1.10–1.12 | 1.11** | 1.10–1.12 |
Gender |
Female | | | | | 1 | |
Male | | | | | 1.12 | 1.00–1.25 |
Age | | | | | 1.17* | 1.02–1.33 |
Self-assessed SES |
Low | | | | | 2.02** | 1.44–2.83 |
Medium | | | | | 1.61** | 1.43–1.80 |
High | | | | | 1 | |
Negative childhood events |
0 events | | | | | 1 | |
1–3 events | | | | | 1.31* | 1.08–1.59 |
4–7 events | | | | | 1.57** | 1.26–1.97 |
8–11 events | | | | | 2.15** | 1.49–3.09 |
Discussion
Main findings
A significant association between RWD and low self-rated health was found among Danish 9th grade pupils. Loneliness and perceived stress, as indicators of mental health, only explained a minor part of the association between RWD and self-rated health.
Interpretation of findings
The association between RWD and self-rated health seems to be unexplored among adolescents [
31‐
45]. Among adults, Moon et al. investigated the relationship between functional literacy/numeracy and self-assessed health and found both to be significantly associated even after controlling for covariates [
32], which is in line with the findings of this study.
According to Zullig et al., adolescents mainly base their self-rated health on their mental health perceptions instead of their physical health [
10]. Therefore, loneliness and perceived stress, as proxies for mental health, were expected to explain a major part of the association between RWD and self-rated health. However, the attenuation of the association between RWD and self-rated health after controlling for loneliness and perceived stress was minor. According to Breidablik et al. and Vingilis et al., self-rated health among adolescents is a multifactorial composite related to both physical health and non-physical health factors such as medical, psychological, social and lifestyle factors [
9,
60]. This may explain why loneliness and perceived stress, as proxies for mental health, explained only a minor part of the association between RWD and self-rated health. Further adjustments in Model 3, did not alter the OR substantially, showing the rest of the covariates having a minor explanatory part in the association. The attenuation driven primarily by loneliness and perceived stress was in line with the argument put forward by Breidablik et al. and Vingilis et al. that self-rated health is a multifactorial composite [
9,
60]. Future research should dive into self-rated health among adolescents to further understand the proposed multifactorial composite and their relationships.
Strengths and limitations
This study was based on self-reported data, which might lead to inaccuracies. However, priority was given to include instruments validated in a Danish setting; SF-36, 10-Item Perceived Stress Scale and MacArthur Scale of Subjective Social Status, which therefore limited misclassifications in the present study. In Denmark, pupils with RWD often have a program on their computer that can read aloud text to speech. As it is expected that the pupils had the opportunity to have the questions read aloud from the computer when answering the questionnaire these inaccuracies are also not expected to be related to RWD. Therefore, the potential misclassifications are expected to be non-differentiated with associations between RWD and self-rated health approaching the null-hypothesis.
Regarding the self-reported measure of RWD, there is a potential risk of differentiated misclassification, as the item has not been validated. However, the aim was not to differentiate between pupils with and without dyslexia, but to differentiate pupils affected by RWD from those without. Future studies should validate the item used to identify pupils with RWD. Furthermore, the dichotomisation of the loneliness variable was based on studies looking at older people [
56,
57]. This is not ideal but we were not able to find studies among adolescents using this variable. Therefore, there is a risk of misclassification with regard to this variable, but this is expected to be non-differentiated.
Of the 10,200 respondents eligible for this study, 452 were excluded as they did not answer the RWD question. The non-response analysis showed more girls than boys answered the RWD question. RWD and self-rated health are both associated with gender, whereas the prevalence of RWD is higher among boys, and girls tend to have a slightly lower self-rated health than boys [
9,
61]. This may lead to underestimated associations between RWD and self-rated health. Self-assessed SES was not significantly associated with non-response, however missing values were present. Sensitivity analyses were performed, having responders and non-responders to RWD with missing values in self-assessed SES allocated to low and high self-assessed SES, respectively (1.36 (95% CI 1.15–1.61), data not shown, Additional file
1). This was repeated but allocating low self-assessed SES to non-responders and high self-assessed SES to RWD responders (1.38 (95% CI 1.16–1.63), data not shown, Additional file
1). Both extreme scenarios did not alter the OR in Model 3, and we are confident that the self-assessed SES did not cause selection bias.
The data was gathered on school-level which could introduce confounding by cluster. The consequence of RWD is expected to be very dependent of the school-environment. If the pupil is attending a school with a very supportive school-environment RWD is not expected to have the same impact, as it would have in a school with a very unsupportive environment. Therefore, we made cluster adjustments on school-level, which further strengthens the internal validity.
Despite that the cohort profile on FOCA concludes that it resembles the Danish background population [
46], the prevalence of RWD are lower in this study than reported in the general population; According to the National Board of Social Services and the Patient’s Handbook, respectively, the prevalence of dyslexia in Denmark is estimated to be between 7 and 20% [
27,
28]. Dyslexia is one branch of RWD, whereas the prevalence of RWD in itself is expected to be higher. The Programme for International Student Assessment (PISA) test conducted in 2015 found that 15% of Danish 15-year olds do not have sufficient functional reading skills [
62]. In comparison, 9.8% of the sample in the present study was affected by RWD, possibly due to excluding pupils at schools for children with special needs.
This study is expected to have a reasonable internal validity, as the potential misclassification is expected to be non-differentiated and selection bias does not seem to threaten our results. It is therefore expected that the association between RWD and self-rated health may be even stronger than shown in the present study because of the low prevalence of RWD. The results may be generalized to adolescents attending public schools in Scandinavia.