The importance of measuring mental health in the same way as mental illness cannot be overstated, because it allows scientists to finally adequately test the hypothesis that mental health and illness belong to two separate continua. Indeed, mental health promotion and protection is premised on the two-continua model because good mental health is presumed to belong to a separate continuum from mental illness (Health and Welfare Canada 1988). Yet, the studies that did exist on the subject only measured mental health emotionally in terms of life satisfaction or happiness (Greenspoon and Saklofske 2001; Headey et al. 1993; Huppert and Whittington 2003; Masse et al. 1998; Suldo and Shaffer 2008). Numerous studies in mainstream psychology of emotion have shown that positive and negative emotions belong to separate continua (e.g., Bradburn 1969; Watson and Clark 1997), but as mentioned earlier, emotional disturbance or emotional vitality does not, in themselves, constitute states of mental illness or mental health.

Findings based MHC-LF in the MIDUS study (Keyes 2005b) support the two-continua model: one continuum indicating the presence and absence of positive mental health and the other indicating the presence and absence of mental illness symptoms. For example, the latent factors of mental illness and mental health correlated (r  = −.53), but only 28.1% of their variance is shared in the MIDUS data (Keyes 2005b). The two-continua model has been replicated in a nationally representative sample of US adolescents (ages 12–18) with data from the Panel Study of Income Dynamics’ Child Development Supplement (Keyes 2009), in a national study of Dutch adults (Westerhof and Keyes 2008, 2010), and in Setswana-speaking South African adults using the MHC-SF (Keyes et al. 2008).

According to the dual-continua model³ shown above, individuals can be categorized by their recent mental illness status and according to their level of mental health—whether they have languishing, moderate, or flourishing mental health. One implication of the dual-continua model is that the absence of mental illness does not imply the presence of mental health. In the American adult population between 25 and 74 years, just over 75% were free of three common mental disorders during the past year (i.e., major depressive episode [MDE], panic disorder [PD], and generalized anxiety [GAD]). However, while just over three-quarters were free of mental illness during the past year, only about 20% were flourishing. A second implication of the dual continua is that the presence of mental illness does not imply the absence of mental health. Of the 23% of adults with any mental illness, 14.5% had moderate, and 1.5% had flourishing mental health. Thus, almost seven of every ten adults with a recent mental illness (MDE, Panic or GAD) had moderate or flourishing mental health. While the absence of mental illness does not mean the presence of mental health (i.e., flourishing), the presence of mental illness does not imply the absence of some level of good mental health.

Another important implication of the dual-continua model is that level of mental health should differentiate level of functioning among individuals free of, and those with, a mental illness. Put differently, anything less than flourishing mental health is associated with impaired functioning both for those with a mental illness and individuals free of a mental illness. Findings consistently show that adults and adolescents who are diagnosed as anything less than flourishing are functioning worse in terms of physical health outcomes, health-care utilization, missed days of work, and psychosocial functioning (Keyes 2002, 2005b, 2006, 2007, 2009a, b). Over all outcomes to date, individuals who are flourishing function better (e.g., fewer missed days of work) than those with moderate mental health, who in turn function better than languishing individuals—and this is true for individuals with a recent mental illness and for individuals free of a recent mental illness.

In the CDS study, the Children’s Depression Inventory (Kovacs 1992) scale was the only measure of mental illness. As a screening tool, the CDI provides a threshold above which youth are expected to screen for depression under clinical assessment. The manual for the CDI recommends slightly different thresholds for boy (a score of 7 or higher) than girls (a score of 6 or higher). For our purposes here, the lower of the threshold, a score of 6 or higher, is used to suggest that an adolescent would screen for depression.

Only 4.9% of flourishing youth would screen for depression, compared with 17.3% of youth with moderate mental health. In sharp contrast, 51.5% of languishing youth would screen for depression. Thus, and compared with flourishing youth, moderately mentally healthy youth are about 3.5 times more likely to screen for depression, and languishing youth are 10.5 times more likely to screen for depression. Compared with moderately mental health youth, languishing youth are about three times more likely to screen for depression.

According to the dual-continua model, level of mental health is hypothesized to differentiate level of psychosocial functioning among individuals with and without a mental disorder. To that end, one-way ANOVAs were used to test whether level of mental health (i.e., languishing, moderate mental health, or flourishing) exerts a main effect in addition to (or interactively with) mental illness (in this case, whether or not youth are above the threshold of a score of 6 or higher on the CDI scale). The outcomes investigated included the four validation scales reported earlier (global self-concept, self-determination, perceived closeness to others, and school integration) as well as conduct problems and helping behavior. For all outcomes, level of mental health exerted a main effect (all F tests, p < .001), with level of conduct problems decreasing, while all other outcomes increased, as level of mental health increased. There was a main effect for the dichotomous variable of mental illness (i.e., whether or not youth had a score of 6 or higher on CDI) for the outcomes of global self-concept (F test, p < .001), school integration (F test, p < .05), and conduct problems (F test, p < .001), but not for the following measures: self-determination, perceived closeness to others, and helping behavior. There were no interaction effects between mental health and mental illness.

Figure 1.2 presents as one example the mean level of perceived integration into school by level of mental health and by mental illness. The main effect for mental illness reveals that perceived integration into school is lower for youth who screen for depression than for youth who would screen as being free of depression, and this is true at all levels of mental health. The main effect for level of mental health reveals that level of perceived integration into school increases as level of mental health increases for youth who would screen as “depression-free” as well as for youth who would screen for depression. In other words, level of mental health matters whether youth have, or do not have, a mental disorder like depression.

How many youth in America are truly mentally healthy, i.e., flourishing in life rather than merely free of mental illness? The CDS study was not designed for the purpose of psychiatric epidemiology of youth; it therefore only provides a single screening measure of depression. Although 14% of youth were screened for depression, the estimate of overall mental illness would likely be higher if the CDS had included measures of anxiety and personality disorders. Yet studies reviewed earlier that used more comprehensive assessments of mental disorders suggest the upper limit of mental illness in youth is about 20%. As such, the findings reported here (14% screening for depression) may not be that far from the best estimate of 20% overall mental illness in youth. What is unique for the CDS is that it permits demarcating the population of youth with a mental illness (as well as without) by level of mental health.

Most youth who screened for depression had moderate mental health (9.7%), while only 1.9% was flourishing and 2.7% was languishing. The fact that the ­proportion of youth who are languishing with possible depression is good news because youth who screen for depression and are languishing function worse than those with moderate mental health (e.g., in terms of conduct problems). Of those who did not screen for depression, only 2.5% is languishing. Languishing in the absence of a mental disorder is rare in youth compared with adults, where languishing in the absence of mental disorders is 9.5% (Keyes 2007). Of those who do not screen for depression, just over 46% of youth are moderately mentally healthy and 37% are flourishing. By comparison, over half (50.8%) of adults otherwise free of an episode of mental disorder are moderately mentally healthy, and only 16.8% of adults are flourishing. Compared with their adult counterparts, youth in the USA are mentally healthier, with just over 20% more youth than adults flourishing.

Despite a long-standing prejudice for scholars and the lay public to equate subjective well-being with emotional well-being (i.e., happiness), research clearly has shown that subjective well-being in US youth and adults is a multifaceted and multidimensional construct. One result of the nearly 50 years of research on this important concept is that researchers have proliferated upward of 13 facets of subjective well-being. In turn, theory and research has supported the metatheoretical models of hedonia and eudaimonia that reflect different kinds of well-being. That is, subjective well-being consists of a cluster of measures reflecting emotional, or hedonic, well-being and a cluster of measures reflecting positive functioning, or eudaimonic, well-being.

Research on the subjective well-being of youth, as with adults, has focused exclusively on the dimension of hedonia, or emotional well-being. However, the research reviewed here indicates that well-being in youth is more complex and whether its structure is equivalent to the structure of subjective well-being found among adults. Findings based on data from the nationally representative CDS sample of youth clearly supported the complex, comprehensive approach to the subjective well-being of youth. That is, among youth ages 12–18, subjective well-being is characterized in terms of distinct dimensions of emotional, psychological, and social well-being. These measures exhibit good construct validity, correlating highly with measures of the quality of one’s self-concept, a youth’s self-determination, as well as the degree to which youth felt integrated into their school. Moreover, the well-being measures also correlated modestly with the Kovacs (1992) Child Depression Inventory and a measure of self-rated overall health and weakly with perceived math and reading skill.

Findings also revealed that levels of emotional well-being are highest, followed closely by psychological well-being, and levels of social well-being are lowest in youth between the ages of 12 and 18. Roughly speaking, these findings suggest that American adolescents experience social well-being about once a week. What this means is that typical American adolescents felt they had something to contribute to the world about once a week; adolescents felt liked they belonged somewhere about once a week; they felt that the way our society works made sense to them about once a week; they felt that our society was becoming a better place about once a week; and our adolescents felt that people in our society were basically good about once a week. It appears more sober when put this way, making it clearer, I hope, that America’s youth sorely lack social well-being. In contrast, youth reported that they experienced psychological well-being (i.e., managing responsibilities, trusting relationships with kids, growth-producing experiences, and confidence to express ideas) about two or three times a week during the past month. However, youth reported that they experienced emotional well-being—i.e., interest in life, happiness, and satisfaction—about every day during the past month.

Is it sufficient to have youth who regularly feel happy, only rarely feel that they have experiences that challenge them to grow and become a better person, but infrequently feel that they have something important to contribute to society? Parents may hope they can raise children who become happy adults; parents probably also aspire to raise children who are and become psychological healthy and socially healthy human beings. Indeed, any nation that claims to prepare its youth to become democratically engaged citizens must have youth who know how to be, and feel, integrated into society, contributing to society, accepting of people not like them, working to improve and understand society, to have a purpose in life, self-accepting and autonomous, but also able to cultivate positive relations with others while exerting some mastery over their immediate environments and, above all, capable of continued personal growth throughout life. A comprehensive approach to the assessment of youth subjective well-being can provide a more detailed picture of the strengths and weakness of our youth, and such an approach will suggest directions for future programmatic initiatives.

Indeed, it must because less than four in every ten American adolescents are flourishing. Findings suggest that fewer adolescents are mentally healthy—nearly 40%—than would be implied by taking the obverse of the best estimate of any mental disorder in youth, which would imply that about 80% or youth are free of a mental illness and therefore mentally healthy. Just over one-half of adolescents fit the criteria for moderate mental health, while 6% were mentally unhealthy, as they fit the criteria for languishing. Moreover, findings here suggest that flourishing may decline, while moderate mental health increases, during adolescence. Nearly one-half of the middle school youth, ages 12–14, were flourishing. Flourishing was the most prevalent mental health status among adolescents aged 12–14; moderate mental health was the most prevalent mental health status among adolescents aged 15–18. These data suggest—although causality cannot be inferred from them—that there is approximately a 10% loss of flourishing between middle school and high school.

Findings support the descriptive hypotheses that flourishing youth function better than moderately mentally healthy youth, who in turn function better than languishing youth. Flourishing youth had the fewest depressive symptoms and conduct problems and the highest levels of global self-concept, self-determination, closeness to other people, and school integration. Languishing youth had the highest number of depressive symptoms and conduct problems and the lowest levels of global self-concept, self-determination, closeness to other people, and school integration. Conduct problems were higher in the older, than younger, adolescents. However, flourishing in both age groups was associated with the lowest level of conduct problems; languishing (i.e., the absence of mental health) was associated with the highest level of conduct problems in both age groups.

Continued research on the epidemiology of children’s mental health in the CDS and other national studies of youth can point toward new directions for prevention of mental illness and for the study of resilience. Findings reviewed thus far in this report indicate that flourishing in adolescence is associated with developmentally desirable outcomes (e.g., low depression, few conduct problems, and high psychosocial functioning). Because these data are cross-sectional, future research is needed to determine the important question of whether positive mental health is a cause or consequence (or both) of conduct problems and psychosocial functioning. What youth are most likely to be flourishing and what factors (intrapersonal, familial, educational, and community) explain how youth come to flourishing over time could provide new insights for promoting positive development and resilience in youth and their transition into adulthood.

Ultimately, the research summarized here raises questions for (1) national public mental health goals and (2) creating effective techniques and interventions for promoting mental health in youth. Nations can no longer blithely announce that they seek to promote the mental health of their citizens while only investing in the study, treatment, and risk reduction and prevention of mental illness. The two-continua model clearly debunks this as a “wanting-doing gap” because we say we want mental health, but we engage in activities directed solely toward mental illness. We cannot promote mental health by solely reducing mental illness, and no amount of wishful political thinking will make this fact go away. We can, of course, politically ignore the fact of the two-continua model, and this will serve only to sacrifice more young lives to the recurrent, chronic, and incurable condition of mental illness. Indeed, I’m not convinced anymore that we, as a nation, can reduce mental illness without promoting mental health.