The rate of psychiatric disorder was significantly higher among individuals belonging to the Low manual class as compared with the High Non-manual class. Compared to High Non-manual class, the risk for psychiatric disorder ranged from 2.07 (Low Manual class) to 1.38 (Low Non-manual class). Parental class had a minor impact on these estimates. Among the Non-manual and Manual classes, downward mobility was associated with increased risk and upward mobility with decreased risk of psychiatric disorder. In addition, downward mobility was inversely associated with the magnitude of social mobility, independent of parental class.

In this prospective cohort study, over 1 million employed Swedes born in 1949-1959 were included. Information on parental class (1960) and own mid-life social class (1980 and 1990) was retrieved from the censuses and categorised as High Non-manual, Low Non-manual, High Manual, Low Manual and Self-employed. After identifying adult class, individuals were followed for psychiatric disorder by first admission of schizophrenia, alcoholism and drug dependency, affective psychosis and neurosis or personality disorder (N=24 659) from the Swedish Patient Register. We used Poisson regression analysis to estimate first admission rates of psychiatric disorder per 100 000 person-years and relative risks (RR) by adult social class (treated as a time-varying covariate). The RRs of psychiatric disorder among the Non-manual and Manual classes were also estimated by magnitude of social mobility.

Social mobility, from parental to adult social class, is suggested to be an important aspect of social stratification that may affect the development of psychiatric disorder [ 9 , 10 ]. Social mobility patterns of psychiatric patients has been studied since the 1950’s [ 9 , 11 - 13 ], whereas the reverse association between social mobility and subsequent psychiatric disorder has been less explored [ 10 , 14 , 15 ]. Downward mobility has been linked to an increased risk of poor self-reported mental health [ 14 ] and alcoholism [ 10 ] among men, but not women. The focus of this paper is to study how social class and social mobility is related to the risk of subsequent psychiatric disorder.

Social class differences in health have been documented throughout the Western world for most major health and mortality outcomes [ 1 - 4 ]. There are several possible factors that may explain the social class differences in health, such as lifestyle, work-related stress, working conditions and financial strain [ 1 , 2 ]. Psychiatric disorder, present in about 10% of the adult population at some point across the life-course, is a major global public health problem [ 5 ]. Previous studies have shown an inverse relation between adult social class and risk for psychiatric disorder [ 6 , 7 ]. In a similar manner, poor psychiatric health in adult life has been linked to low parental social class [ 8 , 9 ].

Materials and Methods

We utilised information from several Swedish population-based, nation-wide registries in this study. All Swedish residents are assigned a unique identification number that stays the same throughout life. This identification number enables linkage of individuals between nationwide Swedish registers by e.g. Statistics Sweden and the National Board of Health and Welfare. Before giving out data for research, the original identification numbers were replaced by a sequence number, unique to each individual. Information about social class was retrieved from the Swedish censuses in 1980 and 1990 and information about parental social class was retrieved from the 1960 Census. The Census-questionnaires were sent to all Swedish registered residents, with mandatory response. The response rate was 99% in the 1960 and 1980 [16] and 98% in the 1990 Census [17]. The censuses included detailed questions about occupations and socioeconomic indicators that allowed construction of the Swedish socioeconomic index (SEI), which was used for classifying social class [18]. The SEI categories are similar to the Erikson, Goldthorpe and Portocarrero (EGP) social class scheme (Table S1). The Swedish Multi-Generation Register, which includes individuals born 1932 or later who lived in Sweden 1961 or later, was used to link children with their parents [19]. The Swedish Patient Register provided data on hospital discharges and diagnoses classified according to the World Health Organisation’s International Classification of Diseases (ICD). The register has a nationwide coverage of patient treatment facilities and includes care in psychiatric as well as somatic hospitals. Sweden has universal and publicly financed health insurance coverage that guarantees equal access to health services, regardless of employment status, socio-economic status or place of residency. The register contains diagnostic information by the treating physician, date of admission and discharge and the name of hospital on virtually all psychiatric hospitalisations since 1973 [20]. The diagnoses are most often given by a specialist in psychiatry and based on observations made during hospitalisation, evaluation of the service user and medical records at discharge. The diagnostic assessment is then forwarded electronically in standardised manner to the National Patient Register. The diagnoses used here, from the register of hospitalised patients, capture severe psychiatric conditions. We used ICD versions 8-10 to identify psychiatric patients and ICD versions 7-9 to identify parental psychiatric disorder (Table S2). The ICD discharge diagnoses for psychiatric disorders recorded in the Swedish Registers are in agreement with diagnoses based on Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria and with those based on semi-structured interviews and medical records [21-23]. The Causes of Death [24] and Total Population Register [25] were used to censor individuals due to death or emigration.

Materials In this prospective cohort study, we included all Swedish individuals born in 1949–1959 who, according to both parental class in 1960 and own adult class in 1980 or 1990, could be linked to an occupational class (Manual, Non-manual, or Self-employed) (Figure 1). We defined psychiatric patients as individuals with a first psychiatric inpatient admission during the period 1980–2005. This group included patients with schizophrenia (N=477), alcoholism (N=11 323) and drug dependency (N=1 850), affective psychosis (N=1 440) and neurosis and personality disorder (N=9 569). Five social classes were used to categorise adult and parental (1960) and adult social class (1980 or 1990): High Non-manual (including intermediate Non-manual), Low Non-manual, High Manual, Low Manual and Self-employed (including farmers). Parental social class was based on the head of the household [26] while adult class was based on the individual’s own class. A conceptual model of social class, social mobility in relation to psychiatric disorder is displayed in Figure S1. For the Non-manual and Manual classes, trajectory-specific social mobility was analysed as downward (-1, -2, -3 steps), upward (+1, +2, +3 steps) and stable (no mobility). The Self-employed were excluded in this part of the analyses due to the difficulty to place this group into a hierarchical order. PPT PowerPoint slide

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larger image TIFF original image Download: Figure 1. Overview of the time-points at which information for the studied subjects and their parents has been retrieved. https://doi.org/10.1371/journal.pone.0077975.g001 We excluded individuals born outside Sweden (N= 14 113), because of differences in both social class attainment and occurrence of psychiatric disorders [27]. Immigrants may be subjected to other as well as additional obstacles to enter the labour market. Further, they may have other types of psychological trauma (from their country of origin) that lead to disparities in psychiatric diagnosis [28]. Individuals who did not have information on adult (N=64 584) or parental (N=43 912) social class were also excluded. Psychiatric disorder was present among 8% of those lacking adult social class information and 5% among those lacking parental social class information, whereas the corresponding figures for included subjects were 2% in both cases. Sex and age were similarly distributed in missing versus non-missing data. To get a more accurate measurement of the effects of social class on subsequent psychiatric disorder, individuals with a psychiatric admission prior to the measurement of adult class were also excluded (N=18 126). In all, 1 016 276 individuals were included in this study, of which 24 659 individuals were hospitalised due to psychiatric disorder during follow-up. Any parental psychiatric hospitalisation occurring before the measurement of adult class in 1980/1990 was identified and grouped according to whether the mother, the father, or both parents had been hospitalised for such a condition. Additional variables included were birth cohort (1949–1954, 1955–1959), age at diagnosis (21–25, 26–30, 31–35, 36–40, 41–45, 46–50, 51–56) and sex.