The main findings of the current study suggest a dose–response relationship indicating that each additional year of delayed HS completion is associated with increased symptom levels of both anxiety and depression. For anxiety, we found that being substantially delayed in completing HS was associated with higher anxiety symptoms for those with lower, but not for those with higher levels of educational attainment. For depression, the association between delayed HS completion and symptom level was found to be consistent across levels of educational attainment.
Our findings concur with those of previous studies in identifying a higher symptom level of both anxiety and depression among individuals with lower educational attainment [1, 4]. A key finding is that the educational gradient in symptom levels of anxiety and depression is not only dependent upon the level of educational attainment, but also upon the time it takes to complete HS. This is supported by the results indicating that symptom levels for both anxiety and depression did not differ between individuals with elementary school as their highest level of educational attainment and those with delayed completion of high school. We also found that individuals with HS as their highest level of educational attainment had lower symptom levels of both depression and anxiety if they completed within a normative timeframe relative to those who spent more than 5 years completing HS.
The association between delayed HS completion and adulthood symptoms of anxiety and depression has, to the authors’ knowledge, not been described in previous studies. Little is therefore known about the mechanisms explaining the increase in symptoms for both anxiety and depression in adulthood among individuals with delayed high school completion. We propose social selection and social causation as two potentially complimentary explanations for this association. A social selection explanation would suggest that individuals with an early onset of CMD or symptoms thereof, will find it more difficult to complete HS. This would correspond well with studies indicating that high symptom levels [22, 23] or internalizing disorders [14, 24] during adolescence are associated with non-completion of HS within the early twenties. A social causation explanation on the other hand, would suggest that the increased symptom levels among individuals with delayed HS completion may be caused by stress related to failing to follow a normative educational progression, or simply by a lack of positive experiences in the school setting. Complementary to this, successful completion of high school could boost mastery and self-efficacy, factors associated with positive mental health. To our knowledge, no studies have investigated the merits of these potential mechanisms regarding delayed completion of HS.
A statistical interaction indicated that delayed HS completion was associated with anxiety symptoms among individuals with lower, but not among those with higher levels of educational attainment. A selection explanation of these findings may suggest that individuals with an early onset of anxiety or a predisposition for developing symptoms of anxiety may be more at risk of being delayed in HS, or being less likely to later successfully complete higher education. While there is some support of non-completion of HS by early twenties associated with early onset disorders [14, 22–24], only one  of three known studies have found that early onset disorders reduce the odds for completing higher educational attainment. The two other studies did not find significant associations between higher educational attainment and mood disorders or anxiety disorders [16, 25]. It is important to note that these results are not entirely comparable to ours as they only include individuals who were admitted to college or university, whereas the current results also include individuals who never attended higher education. A social causation mechanism explanation for these findings could suggest that the combination of delayed HS completion and no higher educational attainment may lead to a particularly difficult life situation with regard to employment, or with other kinds of social stress which in turn could lead to increased symptoms of anxiety.
For depression, we found no interactions, indicating that the associations between educational attainment and normative/delayed HS completion were additive and did not vary across different levels of each other. The absence of interactions illustrates a potentially important difference between the predictors of case-level anxiety and case-level depression. The reasons for these differences should be investigated in studies with repeated measures of CMD throughout adolescence and early adulthood, but is not possible to determine with our current dataset.
A key contribution of the current study is that the results shed light upon delayed HS completion as a largely ignored factor which complicates the much studied relationship between educational attainment and mental health. Several important questions remain unanswered and we encourage future studies to investigate the role of delayed HS completion and mental health in more depth. First, we know little about reasons for delayed HS completion and the extent to which delays caused by reasons other than mental health impairments are associated with mental health outcomes. Second, we do not know the relative contributions of social causation and selection mechanisms in explaining the associations reported herein. Finally, we also do not know whether our results are robust across different countries, school systems, and types of mental disorders.
Limitations of this study include exclusion of population subgroups. The health survey which provided information about common mental disorders did not include institutionalized individuals, minorities with poor Norwegian language skills, and those with severe mental illnesses who are unlikely to respond to surveys. The use of self-reported symptom scales rather than clinical interviews may also be considered a limitation. However, self-report symptom scales also have some advantages as they may be used to capture the importance of sub-clinical symptom levels and how the symptom continuum is associated with other variables.
Strengths of our study include a large sample providing sufficient statistical power, well validated instruments [20, 26], and the use of multiple data-sources.
This study has several implications. For public health and mental health prevention, we believe that screening for case-level anxiety and case-level depression among individuals with delayed HS progression could be beneficial as this group has significantly higher odds of both case-level anxiety and case-level depression relative to those who follow a normative progression. Early identification of individuals at high risk for CMD may in turn be useful for targeted interventions providing counseling with regard to education, employment, or mental health related issues. Our findings also have implications for epidemiological studies as estimates of risk associated with different levels of educational attainment may be misleading when ignoring whether individuals have followed a normative or delayed progression in their studies.