Childhood and adulthood risk factors for socio-economic differentials in psychological distress: evidence from the 1958 British birth cohort
Introduction
Socio-economic differences have been observed across a range of mental disorders, including, schizophrenia, anti-social personality disorder and affective disorders, specifically depression and anxiety (Dohrenwend & Dohrenwend, 1974; Leaf, Weissman, Myers, Tischler, & Holzer, 1984; Dohrenwend, 1990; Bruce, Takeuchi, & Leaf, 1991; Dohrenwend et al., 1992; Kessler et al., 1994; Lewis et al., 1998), most studies showing higher rates of disorder among lower socio-economic groups. For more common mental disorder and distress the findings are less consistent (Dohrenwend & Dohrenwend, 1974; Weich & Lewis, 1998; Stansfeld, Head, & Marmot, 1998a), especially during early adulthood (Macintyre & West, 1991; Glendinning, Love, Hendry, & Shucksmith, 1992; Miech, Caspi, Moffitt, Wright, & Silva, 1999).
In general, socio-economic status differences in health have been attributed to either health selection or to social causation. According to the selection hypothesis, men and women with pre-existing illness drift down the social scale and, conversely, those with better health tend to move up the scale. (Thus, health selection is also referred to as health-related social mobility.) Selection effects may be stronger for some conditions, such as schizophrenia and conduct disorder, than for other conditions, notably affective disorders (Dohrenwend et al., 1992; Miech et al., 1999). Likewise, the strength of selection effects may vary with life stage, with more pronounced effects at the time of labour market entry when the individual's adult social position is established. It has been shown that the influence of psychological disorders on educational achievement commences from early in childhood (Offord et al., 1992) and continues in relation to adolescent conduct disorders (Jayakody, Danziger, & Kessler, 1998; Miech et al., 1999). In turn, education strongly influences adult social position (Caspi, Elder, & Herbener, 1990; Kuh, Head, Hardy, & Wadsworth, 1997). Psychological status may have an impact on adult social position not solely through education, but also through its effect on social functioning, skills and relationships. Thus, selection effects related to psychological status may be stronger at the transition from class of origin to own destination class (inter-generational mobility) than with any changes in social position during adult life (intra-generational mobility). This expectation of greater health selection during inter-generational mobility is not specific to psychological status, but is thought to apply to other health measures (West, 1991).
Alternatively, social causation could explain health differences through the experience of adversity and stressors in low social status, and conversely, with more favourable conditions experienced in higher social groups. Social differences in factors relevant to mental health are evident at each life stage onwards from birth (Power & Matthews, 1997). First during early life, social causation may begin with conditions in the home environment that are regarded as central to the development of emotional well-being (Offord et al., 1992). A broad range of influences may be relevant, some of which are denoted by family structures, such as one-parent families, parental divorce and institutional care (Quinton & Rutter, 1988; Rutter, Quinton, & Hill, 1990); while other dimensions relate to the quality of family functioning, encompassing emotional support and stimulation, parental aspirations and involvement (Brooks-Gunn, Klebanov, Liaw, & Spiker, 1993). Early educational experiences may also contribute to the development of emotional well-being (Hertzman & Wiens, 1996), particularly through the development of self-esteem and mastery, and these will continue to play a role through to adolescence.
Second, social causation may be linked to material disadvantage in childhood or in adult life (Lundberg, 1991; Offord et al., 1992; Weich & Lewis, 1998). Material circumstances could affect psychological status through social comparison, whereby deprived individuals are adversely affected because of perceived inequity (Wilkinson, 1997). Perceived inequity may be greater in societies with larger income inequalities, which in turn, may increase ill-health (Wilkinson, 1997), although this has been questioned (Muntaner & Lynch, 1999). Alternatively, material circumstances may affect other relevant factors, such as educational achievement, family structure and relationships, which in turn may increase the risk of poor mental health, although financial disadvantage may exacerbate or even underlie these risks, for example, as experienced by lone mothers (Brown & Moran, 1997; Hope, Power, & Rodgers, 1999a). Thus, there may be either direct or indirect mechanisms linking material circumstances and psychological status.
Third, social causation includes adult social relationships that impact on adult mental health and that vary by socio-economic status (Turner & Marino, 1994; Stansfeld et al., 1998a). These factors to some extent are a continuation of family functioning and structure (marital status, lone parenthood) in the early home environment, but in adulthood they also include social support and networks. It is well established that divorce and separation are associated with higher rates of psychiatric distress (Bloom, Asher, & White, 1978; Kitson & Morgan, 1990) as demonstrated in the life events literature (Paykel et al., 1969). For women, there may be an additional influence of the burden of childcare, as indexed in many studies by number of children, single motherhood and teenage pregnancy, all of which have been associated with adverse psychological distress (Brown & Harris, 1978; Weissman, Leaf, & Bruce, 1987; McLanahan & Adams, 1989; Maughan & Lindelow, 1997; Lipman, Offord, & Boyle, 1997; Weich, Slogett & Lewis, 1998). Beyond structural factors, quality of social relationships is predictive of mental health. In particular, lack of emotional support and negative aspects of close relationships are associated with higher rates of psychological distress (Oxman, Berkman, Kasl, Freeman, & Barrett, 1992; Stansfeld, Fuhrer, & Shipley, 1998b). Lack of emotional support may also be a vulnerability factor increasing the risk of depression in the face of life events (Brown & Harris, 1978).
Fourth, factors related to labour force participation are part of social causation. There is evidence that unemployment and job insecurity adversely affect a range of mental health outcomes from minor distress to suicide (Banks & Jackson, 1982; Rodgers, 1991a; Burchell, 1994; Ferrie, Shipley, Marmot, Stansfeld, & Davey Smith, 1998; Gunnell et al., 1999). Other conditions at work, including high levels of job demands, low work social support and low decision latitude may influence psychological distress (LaRocco, House, & French, 1980; Wall et al., 1997; Stansfeld, Fuhrer, Shipley, & Marmot, 1999) and decline in psychological functioning (Martikainen, Stansfeld, Hemingway, & Marmot, 1999). Most aspects of labour force participation are strongly patterned by socio-economic position, and in some instances appear to have a strong effect on the social gradient in depressive symptoms (Stansfeld et al., 1998a).
Other factors may be involved in social causation, including, several health related behaviours, although the direction of association with adult mental health is not always well established. Co-morbidity has been shown between alcohol problems and psychiatric disorder (Rodgers et al., 2000) and also, less consistently, between obesity and self esteem (French, Story, & Perry, 1995). Potentially, such factors might contribute to socio-economic differences in psychological status.
Previous studies on socio-economic gradients in psychological status tend to focus on a limited range of explanations and hence, a comprehensive analysis of health selection and social causation is lacking. One exception is a study of psychological distress in the British 1958 birth cohort to age 23 years (Power, Manor, & Fox, 1991; Power & Manor, 1992). This study showed a threefold increase in psychological distress from the highest to lowest social classes in men and a five-fold difference for women. Health selection was evident, although inequalities in psychological distress were largely due to an accumulation of diverse factors from birth onwards rather than to health selection (Power et al., 1991; Power & Manor, 1992). Follow-up of the cohort to age 33 years has shown declining levels of distress among women (Rodgers, Pickles, Power, Collishaw, & Maughan, 1999), but persisting social gradients for both sexes. In the ten years since age 23 there has been a further cumulation of influences regarded as important for adult mental health. During this period, most individuals in Britain complete their education, gain employment, leave the family home and commence their own family. Some individuals had already divorced by age 33 and have experienced detrimental effects on their mental health, particularly for lone-parents (Hope, Rodgers, & Power, 1999b). Our broad purpose is to examine the role of health selection and social causation in the development of social inequalities in psychological distress in the 1958 birth cohort, followed to age 33. Specifically, we assess (i) whether psychological status influences the socio-economic destination that an individual achieves (a) at the time of the transition from social class of origin to own class and (b) within the period of early adulthood; (ii) the impact of health selection on social differences in psychological distress; and finally (iii) the role of social causation, as encompassing factors from early life through to recent years in early adulthood.
Section snippets
Sample
The 1958 birth cohort study comprises all children born in England, Scotland and Wales during one week in March 1958. Data were collected at birth, and at ages 7, 11, 16, 23 and 33. Immigrants to Britain born in the same week were added to the sample at 7, 11 and 16 years. At age 23, 12,537 subjects were interviewed (76% of the target population), and at age 33, 11,405 subjects were interviewed (73% of the target population). As expected, sample attrition has been associated with under
Results
At age 33, 7% of men and 12% women had a high level of psychological distress, but as Fig. 1 shows, the prevalence of distress varied by social class. Among men, levels of distress ranged from 4% of those in professional and managerial classes (I&II) to 12% of those in unskilled manual classes (IV&V). Similarly for women, levels of distress ranged from 7% to 19%, respectively. This social class trend was significant for both sexes (Mantel-Haenszel χ2 49.5 for men, 101.2 for women). The social
Discussion
In this large nationally representative population we found a social gradient in psychological distress in early adulthood, with greater levels of distress among men and women from lower social classes. Following the sequence of events, it emerges that psychological status influences an individual's social destination, but for this cohort at least, this selection process is not a major factor in the development of the social gradient in distress. Other factors accumulating over the lifecourse,
Acknowledgements
This research was supported by a grant from the (UK) Economic and Social Research Council under the Health Variations Programme (L128251021) to Chris Power, Sharon Matthews, Stephen Stansfeld and Orly Manor. CP is a fellow with the Canadian Institute for Advanced Research.
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