A formal model accounting for measurement reliability shows attenuated effect of higher education on intelligence in longitudinal data.

The effect of higher education on intelligence has been examined using longitudinal data. Typically, these studies reveal a positive effect, approximately 1 IQ point per year of higher education, particularly when pre-education intelligence is considered as a covariate in the analyses. However, such covariate adjustment is known to yield positively biased results if the covariate has measurement errors and is correlated with the predictor. Simultaneously, a negative bias may emerge if the intelligence measure after higher education has non-classical measurement errors as in data from the 1970 British Cohort Study that were used in a previous study of the effect of higher education. In response, we have devised an estimation method that used iterated simulations to account for both classical measurement errors in the covariate and non-classical errors in the dependent variable. Upon applying this method in a reanalysis of the data from the 1970 British Cohort Study, we find that the estimated effect of higher education diminishes to 0.4 IQ points per year. Additionally, our findings suggest that the impact of higher education is somewhat more pronounced in the initial 2 years of higher education, aligning with the notion of diminishing marginal cognitive benefits.

Diagnoses of common mental disorders among social workers in Sweden: A register-based cohort study.

BACKGROUND: Little is known about common mental disorders (CMD) diagnoses among social workers, i.e., depression, anxiety, or stress-related disorders. This study aims to examine the risk of CMD among social workers in comparison to other workers and to further investigate differences between men and women and specific occupational titles. METHODS: This register-based cohort study consists of 3,034,304 persons, of which 26,610 were social workers (0.9 % of all workers), aged 30-64 years, living in Sweden in 2015. The risk of diagnosed CMDs was followed up until 2020. Cox regression models were used to calculate hazard ratios (HR) and 95 % confidence intervals (CI), adjusting for sex, birth country, education, and birth year. RESULTS: The participants were followed up by a total of 16,833,742.9 person-years, with an average follow-up of 5.5 years. Social workers, compared to other workers, were at a higher risk of CMD (HR 1.3, 95 % CI 1.2-1.4) after adjustment. The HR was equal, 1.3, for depression (95 % CI 1.2-1.5) and anxiety or stress-related disorder (95 % CI 1.2-1.4). The association between social work and CMD was stronger among men (HR 1.7, 95 % CI 1.6-1.9) compared to women (HR 1.2, 95 % CI 1.1-1.3). Further, men working as assistance analysts had the highest risk among the occupational categories (HR 2.2, 95 % CI 1.2-3.9). LIMITATIONS: CMD diagnoses only included cases treated in secondary care. CONCLUSIONS: Social workers, especially male social workers, had a higher risk of CMD. This deserves attention for future research and interventions aimed at improving the mental health of social workers.

The role of working conditions in educational differences in all-cause and ischemic heart disease mortality among Swedish men.

OBJECTIVES: This study aims to investigate the extent to which low job control and heavy physical workload in middle age explain educational differences in all-cause and ischemic heart disease (IHD) mortality while accounting for important confounding factors. METHODS: The study is based on a register-linked cohort of men who were conscripted into the Swedish military at around the age of 18 in 1969/1970 and were alive and registered in Sweden in 2005 (N=46 565). Cox proportional hazards regression models were built to estimate educational differences in all-cause and IHD mortality and the extent to which this was explained by physical workload and job control around age 55 by calculating the reduction in hazard ratio (HR) after adjustments. Indicators of health, health behavior, and other factors measured during conscription were accounted for. RESULTS: We found a clear educational gradient for all-cause and IHD mortality (HR 2.07 and 2.47, respectively, for the lowest compared to the highest education level). A substantial part was explained by the differential distribution of the confounding factors. However, work-related factors, especially high physical workload, also played important explanatory roles. CONCLUSION: Even after accounting for earlier life factors, low job control and especially high physical workload seem to be important mechanistic factors in explaining educational inequalities in all-cause and IHD mortality. It is therefore important to find ways to reduce physical workload and increase job control in order to decrease inequalities in mortality.

The impact of cardiorespiratory fitness and physical workload on disability pension-a cohort study of Swedish men.

OBJECTIVE: Understanding the impact of physical capacity in combination with high physical workload could be beneficial for the prevention of health-related exits from work. Therefore, the aim of this study was to investigate the separate and combined effects of low cardiorespiratory fitness and high physical workload on disability pension (DP) due to any cause, musculoskeletal disorders (MSD), and cardiovascular diseases (CVD). METHODS: A total of 279 353 men born between 1951 and 1961 were followed regarding DP between 2006 and 2020, ages 45-64. Cardiorespiratory fitness was assessed during military conscription, using an ergometer bicycle test. Physical workload was based on a job-exposure matrix (JEM) linked to occupational title in 2005. Cox regression models estimated separate and combined associations with DP. RESULTS: Low cardiorespiratory fitness and high physical workload were associated with increased risk of DP. For all cause DP, the fully adjusted hazard ratio and 95% confidence interval for those with low cardiorespiratory fitness was 1.38 (1.32-1.46) and for those with high physical workload 1.48 (1.39-1.57). For all cause and MSD DP, but not for CVD DP, the combination of low cardiorespiratory fitness and high physical workload resulted in higher risks than when adding the effect of the single exposures. CONCLUSION: Both low cardiorespiratory fitness in youth and later exposure to high physical workload were associated with an increased risk of DP, where workers with the combination of both low cardiorespiratory fitness and a high physical workload had the highest risks (all-cause and MSD DP).

The meaning of decision latitude in registered nurses' night work.

PURPOSE: For many employees today, the work situation and work content differ from those of the industrial workers that were originally in mind when the well-known demand-control-support model was developed. The aim of this study was to gain a deeper understanding of the meaning of control, i.e., decision latitude, in post-industrial society, using night-working registered nurses as an example. METHODS: As an example of a modern human service occupation in a value-based organization we choose registered nurses. Twenty-nine registered nurses from 11 departments at three different hospitals participated in semi-structured interviews. The analysis used a thematic approach and was deductive, based on an operationalization of decision latitude. RESULTS: Findings indicate that the specific meaning of decision latitude is influenced by the specific work organization. Moreover, decision latitude appears to interact in a complex way with demands and support at work. CONCLUSIONS: Decision latitude appears to be influenced by the specific work organization. Thus, when we address self-reported decision latitude, it can have different meanings and potentially different effects in different contexts. Moreover, the interface and interplay between the three constructs decision latitude, demand and support seems to be relevant and complex.

Trajectories of psychosocial working conditions and all-cause and cause-specific mortality: a Swedish register-based cohort study.

OBJECTIVES: While psychosocial working conditions have been associated with morbidity, their associations with mortality, especially cause-specific mortality, have been less studied. Additionally, few studies considered the time-varying aspect of exposures. We aimed to examine trajectories of job demand-control status in relation to all-cause and cause-specific mortality, including cardiovascular diseases (CVD), suicide, and alcohol-related mortality. METHODS: The study population consisted of around 4.5 million individuals aged 16-60 years in Sweden in 2005. Job control and demands were respectively measured using job exposure matrices (JEM). Trajectories of job control and demands throughout 2005-2009 were identified using group-based trajectory modelling, and job demand-control categories were subsequently classified. Deaths in 2010-2019 were recorded in the national cause of death register. Cox regression models were used. RESULTS: A total of 116 242 individuals died in 2010-2019. For both job control and demands, we identified four trajectories, which were parallel to each other and represented four levels of exposures. Low control and passive jobs were associated with higher all-cause, CVD, and suicide mortality among both men and women. High strain jobs were associated with higher all-cause and CVD mortality among men, while low control, passive jobs, and high strain jobs were associated with higher alcohol-related mortality among women. CONCLUSIONS: The trajectories identified may suggest stable levels of job control and demands over time. Poor psychosocial working conditions are related to all-cause and cause-specific mortality, and these patterns vary to some extent between men and women.

Job demands and job control and their associations with disability pension-a register-based cohort study of middle-aged and older Swedish workers.

OBJECTIVES: Job demands and control at work and their combination, job strain, have been studied in relation to risk of disability pension (DP) previously. In the present study, based on registry data, we aimed to deepen the knowledge by analyzing major disease groups among the DPs, dose-response shape of the associations, and potential confounding effects of physical workload. METHODS: Approximately 1.8 million workers aged 44 or older and living in Sweden in 2005 were followed up for 16 years, up to a maximum of 65 years of age. We linked mean values of job demands and job control, estimated in a job-exposure matrice (JEM) by gender, to individuals through their occupational titles in 2005. These values were categorized by rank order, and, for the construction of job-strain quadrants, we used a median cut-off. Associations with DP were estimated in Cox proportional-hazards models. RESULTS: In models accounting for covariates including physical workload, low levels of job control were associated with higher risk of DP among both men and women. This association was most clear for DP with a psychiatric diagnosis, although a dose-response shape was found only among the men. High levels of job demands were associated with decreased risk of DP across diagnoses among men, but the same association varied from weak to non-existing among women. The high- and passive job-strain quadrants both showed increased risk of DP with a psychiatric diagnosis. CONCLUSION: The results suggest that, at the occupational level, low job control, but not high job demands, contributes to an increased incidence of DP, particularly regarding DP with a psychiatric diagnosis.

Combined exposure to heavy physical workload and low job control and the risk of disability pension: A cohort study of employed men and women in Sweden.

OBJECTIVE: To investigate the separate and combined effects of overall heavy physical workload (PWL) and low decision authority on all-cause disability pension (DP) or musculoskeletal DP. METHODS: This study uses a sample of 1,804,242 Swedish workers aged 44-63 at the 2009 baseline. Job Exposure Matrices (JEMs) estimated exposure to PWL and decision authority. Mean JEM values were linked to occupational codes, then split into tertiles and combined. DP cases were taken from register data from 2010 to 2019. Cox regression models estimated sex-specific Hazard Ratios (HR) with 95% confidence intervals (95% CI). The Synergy Index (SI) estimated interaction effects. RESULTS: Heavy physical workload and low decision authority were associated with an increased risk of DP. Workers with combined exposure to heavy PWL and low decision authority often had greater risks of all-cause DP or musculoskeletal DP than when adding the effects of the single exposures. The results for the SI were above 1 for all-cause DP (men: SI 1.35 95%CI 1.18-1.55, women: SI 1.19 95%CI 1.05-1.35) and musculoskeletal disorder DP (men: SI 1.35 95%CI 1.08-1.69, women: 1.13 95%CI 0.85-1.49). After adjustment, the estimates for SI remained above 1 but were not statistically significant. CONCLUSION: Heavy physical workload and low decision authority were separately associated with DP. The combination of heavy PWL and low decision authority was often associated with higher risks of DP than would be expected from adding the effects of the single exposures. Increasing decision authority among workers with heavy PWL could help reduce the risk of DP.

Utilizing a Nordic Crosswalk for Occupational Coding in an Analysis on Occupation-Specific Prolonged Sickness Absence among 7 Million Employees in Denmark, Finland, Norway and Sweden.

We identified occupations with a high incidence of prolonged sickness absence (SA) in Nordic employees and explored similarities and differences between the countries. Utilizing data from national registers on 25-59-year-old wage-earners from Denmark, Finland, Norway and Sweden, we estimated the gender- and occupation-specific age-adjusted cumulative incidence of SA due to any cause, musculoskeletal diseases and mental disorders. To increase the comparability of occupations between the countries, we developed a Nordic crosswalk for occupational codes. We ranked occupational groups with the incidence of SA being statistically significantly higher than the population average of the country in question and calculated excess fractions with the employee population being the reference group. We observed considerable occupational differences in SA within and between the countries. Few occupational groups had a high incidence in all countries, particularly for mental disorders among men. In each country, manual occupations typically had a high incidence of SA due to any cause and musculoskeletal diseases, while service occupations had a high incidence due to mental disorders. Preventive measures targeted at specific occupational groups have a high potential to reduce work disability, especially due to musculoskeletal diseases. Particularly groups with excess SA in all Nordic countries could be at focus.

Does a change to an occupation with a lower physical workload reduce the risk of disability pension? A cohort study of employed men and women in Sweden.

OBJECTIVE: This study aimed to examine if a change to an occupation with a lower physical workload reduces the risk of all-cause disability pension (DP) and musculoskeletal DP (MDP). METHODS: This study used a sample of 359 453 workers who were registered as living in Sweden in 2005 and aged 44-63 in 2010. Exposure to physical workload was measured from 2005-2010 by linking a mean value from a job exposure matrix to occupational codes. The mean values were then split into quartiles. All included participants had high exposure to physical workload (top quartile) from 2005-2007. A change in physical workload was measured as a change to (i) any lower quartile or (ii) medium-high or low quartiles from 2008-2010. DP cases were taken from register data from 2011-2016. Crude and multivariate Cox proportional-hazards regression models estimated sex-specific hazard ratios (HR) with 95% confidence intervals (CI). RESULTS: Compared to workers with consistently high physical workload, a change to any lower quartile of physical workload was associated with a decreased risk of all-cause DP (men: HR 0.59, 95% CI 0.46-0.77, women: HR 0.63, 95% CI 0.52-0.76) and MDP (men: HR 0.52, 95% CI 0.31-0.89, women: HR 0.61, 95% CI 0.44-0.84). Older workers had the largest decreased risk for MDP. Generally, changing from high to low physical workload was associated with a greater reduced risk of DP than changing from high to medium-high physical workload. CONCLUSIONS: Changing to an occupation with lower exposure to physical workload was associated with reduced risks of DP and MDP among both sexes.

Job control, job demands and job strain and suicidal behaviour among three million workers in Sweden.

OBJECTIVE: To investigate the association between job control, job demands and their combination (job strain) and suicide attempts and deaths among male and female workers in Sweden. METHODS: Job control and demands were measured separately for men and women using a job exposure matrix, which was linked to around three million individuals based on their occupational title in 2005. Suicide attempts and deaths were measured in the hospital and cause of death registers from 2006 to 2016. HRs were estimated using discrete proportional hazards models with annually updated age as the time axis. Models were adjusted for sociodemographic, family, health, labour market and childhood factors, as well as the time-varying effects of unemployment, sick leave and family factors during follow-up. RESULTS: Low job control was associated with an increased risk of suicide attempts and deaths among both men and women while high job demands tended to be associated with a decreased risk. The combination of job control and job demands (job strain) reflected the increased risk of low control jobs and the decreased risk of high demand jobs. Associations were attenuated but still present after adjustments. CONCLUSIONS: Low job control is related to suicide attempts and deaths, and this is only partially explained by important covariates measured both prebaseline and during follow-up. Attempts to increase job control among workers may be beneficial in preventing suicide.

Educational qualification differences and early labor market exit among men: the contribution of labor market marginalization measured across the working life.

BACKGROUND: The present study aims to investigate the association between educational qualification and early labor market exit among men and to examine the contribution of labor market marginalization measured across the working life on this association. METHOD: A register-linked cohort study was conducted including men who completed military service in 1969/70 (born between 1949 and 1951) and were alive at age 55 and not disability pension beneficiaries (n = 40 761). Information on the highest level of educational qualification and the outcome of early exit (disability pension, sickness absence, unemployment, and early old-age pension) was obtained from Swedish nationwide registers between the ages of 55 and 64 years. Labor market marginalization was defined as periods of long-term unemployment and sickness absence over the working life and up to follow-up. Cox regression analyses were used to obtain hazard ratios (HR) with 95% confidence intervals (CI). RESULTS: Low-educated men were more likely to leave the labor force early due to disability pension or sickness absence (HR: 2.48), unemployment (HR: 2.09), and early old-age pension with- (HR:1.25) and without -income (HR: 1.58). Labor market marginalization across the working life explained a large part of the association for the more involuntary early exit routes (disability pensions, sickness absence, unemployment) and explained very little with regards to the more voluntary early exit routes (early old-age pension with and without income). CONCLUSION: Exposure to labor market marginalization across the working life was important in explaining educational differences in early labor market exit due to disability pension or sickness absence and unemployment. This study underscores the importance of identifying and implementing preventive measures in the workplace (e.g. adaptions) to prevent new spells of sickness absence and unemployment, especially among low educated individuals.

Long-term sick leave for back pain, exposure to physical workload and psychosocial factors at work, and risk of disability and early-age retirement among aged Swedish workers.

PURPOSE: To assess the risk of disability and early-age retirement associated with previous long-term sickness absence for back pain (back-pain SA), exposure to high physical workload, low job control, high demands and high strain, and to evaluate effect modification by work factors on the relationship between back-pain SA and premature retirement. METHODS: All employed Swedish residents born 1946-1955 (n = 835,956) were followed up from 2010 to 2016 for disability (DP) and early-age pension (EAP). Associations of premature retirement with exposure to work factors and back-pain SA in the 3 years before follow-up were estimated through proportional hazards models. Retirement, back-pain SA and covariates were assessed through administrative sources, and exposure to work factors through a job-exposure matrix. RESULTS: In both genders, back-pain SA was associated with DP (> 1 episode: HR 3.23 among men; HR 3.12 among women) and EAP (> 1 episode: HR 1.24 among men; HR 1.18 among women). Higher physical workload and lower job control were also associated with an increased DP risk in both genders, whereas higher job demands showed a decreased risk. For EAP, associations with work factors were weak and inconsistent across genders. No effect modification by work factors was found, except for a negative effect modification by job strain on DP risk among women, i.e. a reduced effect of back-pain SA with increasing exposure. CONCLUSION: Back-pain SA was a significant predictor of both DP and EAP, while work factors were consistently associated only with DP. Our results indicate that the joint effect of back-pain SA and work factors on DP is additive and does not support effect modification by work factors.

Psychosocial workplace factors and alcohol-related morbidity: a prospective study of 3 million Swedish workers.

BACKGROUND: Psychosocial workplace factors may be associated with alcohol-related morbidity, but previous studies have had limited opportunities to take non-occupational explanatory factors into account. The aim of this study is to investigate associations between job control, job demands and their combination (job strain) and diagnosed alcohol-related morbidity while accounting for several potentially confounding factors measured across the life-course, including education. METHODS: Job control, job demands and job strain were measured using the Swedish job exposure matrix measuring psychosocial workload on the occupational level linked to over 3 million individuals based on their occupational titles in 2005 and followed up until 2016. Cox regression models were built to estimate associations with alcohol-related diagnoses recorded in patient registers. RESULTS: Low job control was associated with an increased risk of alcohol-related morbidity, while high job demands tended to be associated with a decreased risk. Passive and high-strain jobs among men and passive jobs among women were also associated with an increased risk of alcohol diagnoses. However, all associations were found to be weakened in models adjusted for other factors measured prospectively over the life-course, especially in models that included level of education. CONCLUSION: The associations between low job control and high job demands, and the risk of alcohol-related morbidity reflect underlying socioeconomic differences to some extent. Lower job control, however, remained associated with a higher risk of alcohol-related morbidity.

Depression among teachers: a Swedish register-based study.

BACKGROUND: Some studies have suggested that teachers are particularly at risk for mental health problems but the research in this area has not been conclusive. This study aims to compare the risk of being diagnosed with depression for different types of teachers in Sweden, both with each other and with the rest of the population, using register data. METHODS: Just over 3 million individuals age 30-60 were included of which 256,166 were teachers. The exposure variable was the occupation held in 2005 and the outcome was any diagnosis of depression during the follow up period of 2006 to 2016. The data was analyzed using Cox proportional hazard regression. RESULTS: Around 5 % of women and 3 % of men developed depression during the follow up. For women, teachers had a decreased risk of developing depression compared to non-teachers, but this association was no longer present after adjusting for common covariates including education. For men, teachers had an increased risk of depression both before and after adjustment (HR 1.27 95% CI 1.22-1.32). When comparing different kinds of teachers to university teachers, several types of teachers including primary and special education teachers had an increased risk among men while primary and secondary teachers had a decreased risk among women. CONCLUSION: The increased risk of depression in male teachers is a result that requires further exploration in terms of occupational differences between male and female teachers.

Personality trait by intelligence interaction effects on grades tend to be synergistic.

BACKGROUND: Earlier research has identified both synergistic and compensatory personality traits by intelligence interaction effects on academic performance. METHODS: The present study employed data on intelligence, personality traits, and academic performance in the 1997 National Longitudinal Survey of Youth (NLSY97, N = 8984). RESULTS: Some intelligence by personality trait interaction effects, mainly involving indicators of dependability, on high school grades were identified. The interaction effects tended to be synergistic, meaning that the association between the trait and grades tended to strengthen with increased intelligence. A positive association between intelligence and the reliability in the measurement of a dependability composite score accounted for a substantial portion of the synergistic dependability by intelligence interaction effect on academic performance. CONCLUSIONS: Personality trait by intelligence interaction effects on academic performance tend to be synergistic and may, at least to some degree, be due to a positive association between intelligence and reliability in the measurement of personality traits.

Dangers of residual confounding: a cautionary tale featuring cognitive ability, socioeconomic background, and education.

BACKGROUND: Cognitive ability and socioeconomic background (SEB) have been previously identified as determinants of achieved level of education. According to a "discrimination hypothesis", higher cognitive ability is required from those with lower SEB in order to achieve the same level of education as those with higher SEB. Support for this hypothesis has been claimed from the observation of a positive association between SEB and achieved level of education when adjusting for cognitive ability. We propose a competing hypothesis that the observed association is due to residual confounding. METHODS: To adjudicate between the discrimination and the residual confounding hypotheses, data from the 1997 National Longitudinal Survey of Youth (NLSY97, N = 8984) was utilized, including a check of the logic where we switched predictor and outcome variables. RESULTS: The expected positive association between SEB and achieved level of education when adjusting for cognitive ability (predicted by both hypotheses) was found, but a positive association between cognitive ability and SEB when adjusting for level of education (predicted only by the residual confounding hypothesis) was also observed. CONCLUSIONS: These results highlight the potential use of reversing predictors and outcomes to test the logic of hypothesis testing, and support a residual confounding hypothesis over a discrimination hypothesis in explaining associations between SEB, cognitive ability, and educational outcome.

A comparison of models with weight, height, and BMI as predictors of mortality.

INTRODUCTION: Body mass index (BMI) is a composite variable of weight and height, often used as a predictor of health outcomes, including mortality. The main purpose of combining weight and height in one variable is to obtain a measure of obesity independent of height. It is however unclear how accurate BMI is as a predictor of mortality compared with models including both weight and height or a weight × height interaction as predictors. METHODS: The current study used conscription data on weight, height, and BMI of Swedish men (N = 48,904) in 1969/70 as well as linked data on mortality (3442 deaths) between 1969 and 2008. Cox proportional hazard models including combinations of weight, height, and BMI at conscription as predictors of subsequent all-cause and cause-specific mortality were fitted to data. RESULTS: An increase by one standard deviation on weight and BMI were associated with an increase in hazard for all-cause mortality by 5.4% and 11.5%, respectively, while an increase by one standard deviation on height was associated with a decrease in hazard for all-cause mortality by 9.4%. The best-fitting model indicated lowest predicted all-cause mortality for those who weighed 60.5 kg at conscription, regardless of height. Further analyses of cause-specific mortality suggest that this weight seems to be a compromise between lower optimal weights to avoid cancer and CVD mortality and a higher optimal weight to not die by suicide. CONCLUSIONS: According to the present findings, there are several ways to make better use of measured weight and height than to calculate BMI when predicting mortality.