Generational differences in mental health trends in the twenty-first century.

Given the observed deterioration in mental health among Australians over the past decade, this study investigates to what extent this differs in people born in different decades-i.e., possible birth cohort differences in the mental health of Australians. Using 20 y of data from a large, nationally representative panel survey (N = 27,572), we find strong evidence that cohort effects are driving the increase in population-level mental ill-health. Deteriorating mental health is particularly pronounced among people born in the 1990s and seen to a lesser extent among the 1980s cohort. There is little evidence that mental health is worsening with age for people born prior to the 1980s. The findings from this study highlight that it is the poorer mental health of Millennials that is driving the apparent deterioration in population-level mental health. Understanding the context and changes in society that have differentially affected younger people may inform efforts to ameliorate this trend and prevent it continuing for emerging cohorts.

Detecting Cohort Effects in Accelerated Longitudinal Designs Using Multilevel Models.

Accelerated longitudinal designs allow researchers to efficiently collect longitudinal data covering a time span much longer than the study duration. One important assumption of these designs is that each cohort (a group defined by their age of entry into the study) shares the same longitudinal trajectory. Although previous research has examined the impact of violating this assumption when each cohort is defined by a single age of entry, it is possible that each cohort is instead defined by a range of ages, such as groups that experience a particular historical event. In this paper we examined how including cohort membership in linear and quadratic multilevel models performed in detecting and controlling for cohort effects in this scenario. Using a Monte Carlo simulation study, we assessed the performance of this approach under conditions related to the number of cohorts, the overlap between cohorts, the strength of the cohort effect, the number of affected parameters, and the sample size. Our results indicate that models including a proxy variable for cohort membership based on age at study entry performed comparably to using true cohort membership in detecting cohort effects accurately and returning unbiased parameter estimates. This indicates that researchers can control for cohort effects even when true cohort membership is unknown.

Use of 2-Stage Modeling to Identify How Colorectal Cancer Risk Changes With Period and Cohort.

Colorectal cancer (CRC) incidence rates have decreased among adults aged 50 years or older while increasing in adults under age 50 years. Understanding these trends is challenging because of the multiple related time scales of age, diagnosis period, and birth cohort. We analyzed incidence rates of rectal, distal colon, and proximal colon cancer for individuals aged 20 years or more from the Surveillance, Epidemiology, and End Results Program for diagnosis years 1978-2017. We used a 2-stage generalized linear model to determine age, period, and cohort effects for CRC incidence. We first estimated birth cohort effects among people under age 45 years. We used these results to specify prior distributions for cohort effects in a Bayesian model to estimate period effects among people aged 45 years or more. There was no evidence of period effects for people under age 45 years. Risks of rectal and distal colon cancer increased for later birth cohorts. Compared with the 1943-1952 birth cohort, the 1983-1992 birth cohort had 2.2 times the risk of rectal cancer, 1.9 times the risk of distal colon cancer, and 1.3 times the risk of proximal colon cancer. For people aged ≥45 years, period effects showed declines in CRC risk that were attributable to screening.

Intimate partner violence linked to gambling: cohort and period effects on the past experiences of older women.

BACKGROUND: Problem gambling increases the risk of experiencing intimate partner violence (IPV). People impacted by gambling-related IPV face distinctive challenges, and these may be compounded by intersections with gender, generational influences and contextual factors. This study explored the past experiences of older women affected by male partner violence linked to gambling, and how these were shaped by cohort and period effects and problem gambling. Cohort effects are the generational characteristics of a group born at a particular time, while period effects relate to prevailing external conditions at the time of the abuse, including laws, services and practices. METHODS: A larger study exploring the nature of the relationship between problem gambling and IPV recruited 72 women through help services and advertising. The current study analysed a subset of interviews with 22 women aged 50 years or over. We analysed the data using adaptive grounded theory to explore the intersection between IPV, gambling, and cohort and period effects. RESULTS: Cohort effects on the women's experiences of IPV included gendered attitudes, traditional views of marriage, silence surrounding IPV, reticence to disclose the abuse, and little understanding of problem gambling. These influences deterred women from questioning their partner's gambling, and to instead keep the gambling and abuse hidden. Many women did not recognise abuse linked to gambling as IPV, since gambling was considered a normal, harmless pastime. Having a gambling problem exacerbated violence and coercive control by male partners as traditional gender norms supported male authority over their female partner. Women with a gambling problem sometimes felt they deserved the abuse. Period effects included a lack of IPV and gambling services, gendered service responses, failure to prioritise the women's safety, and no consideration by services of the role of gambling in the abuse. CONCLUSION: Reducing gender inequality is critical to reduce male partner violence towards women. Women impacted by gambling-related IPV, including the legacy of past abuse, need service responses that recognise all forms of abuse, understand the historical and contextual factors that exacerbate it, and recognise how gambling can amplify IPV. A reduction in problem gambling is needed to reduce gambling-related IPV.

Understanding the longitudinal dynamics of rural-urban mental health disparities in later life in China.

OBJECTIVES: Understanding longitudinal patterns of rural-urban mental health disparities is vital for effective intervention and policy development in China. However, few studies have estimated separate effects of birth-cohort and ageing and examined the role of community resources on health inequalities. METHODS: Drawing data from the China Health and Retirement Longitudinal Study (2011-2018), this study employed multilevel modelling to identify the mental health trajectories of rural, peri-urban, urban older adults by cohort and the community effects. RESULTS: The changes in the mental health gap between rural, peri-urban and urban older adults over time varied by birth cohorts. Among younger cohorts aged under 65, the mental health disparities between rural, peri-urban and urban residents increased as they got older. Underdeveloped community infrastructure greatly explained the rural health disadvantage. CONCLUSION: The study indicates increasing rural-urban health disparities at the onset of later life. Improving community infrastructure in rural and peri-urban areas is vital to minimise rural-urban health gaps.

Age, Period, and Cohort Trends in Perceived Mental Health Treatment Need and Differences by Mental Health Severity in the United States, 2008-2019.

Identifying age, period, and cohort trends in perceived mental health treatment need over time by mental illness severity is important to identify where to focus early intervention efforts. We included adults who did not report receiving past-year mental health treatment in the 2008-2019 National Survey on Drug Use and Health (N = 364,676). Hierarchical age-period-cohort models were used to assess perceived mental health treatment need, adjusting for demographics stratified by mental illness severity (none, any but not severe [AMI], severe [SMI]). Median odds ratios estimated cohort and period variance. Cohort effects explained a significant portion of the variance over time; period effects were minimal. Perceived mental health treatment need was highest among adults with AMI from recent birth cohorts (2000-2002: ß = 1.12; 95% CI = 0.96, 1.28). Efforts are needed to address increases in perceived mental health treatment need in younger birth cohorts, such as removing structural barriers (e.g., healthcare system barriers).

Age, Period, and Cohort Effects of Internalizing Symptoms Among US Students and the Influence of Self-Reported Frequency of Attaining 7 or More Hours of Sleep: Results From the Monitoring the Future Survey 1991-2019.

Adolescent internalizing symptoms have increased since 2010, whereas adequate sleep has declined for several decades. It remains unclear how self-reported sleep attainment has affected internalizing-symptoms trends. Using 1991-2019 data from the Monitoring the Future Study (n ~ 390,000), we estimated age-period-cohort effects in adolescent internalizing symptoms (e.g., loneliness, self-esteem, self-derogation, depressive affect) and the association with yearly prevalence of a survey-assessed, self-reported measure of attaining ≥7 hours of sleep most nights. We focused our main analysis on loneliness and used median odds ratios to measure variance in loneliness associated with period differences. We observed limited signals for cohort effects and modeled only period effects. The feeling of loneliness increased by 0.83% per year; adolescents in 2019 had 0.68 (95% CI: 0.49, 0.87) increased log odds of loneliness compared with the mean, which was consistent by race/ethnicity and parental education. Girls experienced steeper increases in loneliness than boys (P < 0.0001). The period-effect median odds ratio for loneliness was 1.16 (variance = 0.09; 95% CI: 0.06, 0.17) before adjustment for self-reported frequency of getting ≥7 hours sleep versus 1.07 (variance = 0.02; 95% CI: 0.01, 0.03) after adjustment. Adolescents across cohorts are experiencing worsening internalizing symptoms. Self-reported frequency of <7 hours sleep partially explains increases in loneliness, indicating the need for feasibility trials to study the effect of increasing sleep attainment on internalizing symptoms.

Acting Like a Baby Boomer? Birth-Cohort Differences in Adults' Personality Trajectories During the Last Half a Century.

Society and developmental theory generally assume that there are wide generational differences in personality. Yet evidence showing historical change in the levels of adult Big Five traits is scarce and particularly so for developmental change. We tracked adult trajectories of personality in 4,732 participants (age: M = 52.93 years, SD = 16.69; 53% female) from the Seattle Longitudinal Study (born 1883-1976) across 50 years. Multilevel models revealed evidence for historical change in personality: At age 56, later-born cohorts exhibited lower levels of maturity-related traits (agreeableness and neuroticism) and higher levels of agency-related traits (extraversion and openness) than earlier-born cohorts. Historical changes in agreeableness and neuroticism were more pronounced among young adults, but changes in openness were less pronounced. Cohort differences in change were rare and were observed only for agreeableness; within-person increases were more pronounced among later-born cohorts. Our results yield the first evidence for historical change in the Big Five across adulthood and point to the roles of delayed social-investment and maturity effects.

Shifting educational gradients in body mass index trajectories of Indonesians: an age period cohort analysis.

BACKGROUND: Globally, the number of obese adults has increased rapidly in many developing countries. The links between increased educational attainment and lower risks of overweight/obesity have been studied in a number of high-income contexts. However, educational attainment can have a different association with obesity at different levels of economic development and different stages of the nutritional transition, and these associations may vary by period and cohort. This study aims to provide evidence on the shifting of educational gradients in overweight/obesity in Indonesia, a low middle income country. METHODS: Using five waves of Indonesian Family Life Survey (IFLS), this study examines the Body Mass Index (BMI) trajectories of 14,810 individuals from 1993 to 2014. This study analyses how educational gradients in BMI have shifted over time and across cohorts using a hierarchical age-period-cohort (HAPC) model to account for the effects of age and the changes in historical periods (social and environmental contexts). RESULTS: In older generations, higher educational attainment is associated with higher BMI, but the gap between educational groups shrinks in more recently-born cohorts. The BMI of lower educational groups is catching up with that of the tertiary educated, leading to an increased risk of overweight/obesity among low educated individuals. Having tertiary education lowers the risk of weight gain (-0.04 point) among recently-born cohort of women, but it still increases the risk (+ 0.04 point) for men. CONCLUSION: Changes in access to education and the ongoing nutritional transition in Indonesia are leading to a shifting of educational gradients in overweight/obesity over time. The rising trends in BMI among low-educated and younger individuals are of substantial concern for Indonesian public health due to their implications for the risk of communicable and non-communicable diseases in the future.

How is the distribution of psychological distress changing over time? Who is driving these changes? Analysis of the 1958 and 1970 British birth cohorts.

AIMS: The main objective of this study was to investigate distributional shifts underlying observed age and cohort differences in mean levels of psychological distress in the 1958 and 1970 British birth cohorts. METHODS: This study used data from the 1958 and 1970 British birth cohorts (n = 24,707). Psychological distress was measured by the Malaise Inventory at ages 23, 33, 42 and 50 in the 1958 cohort and 26, 34, 42 and 46-48 in the 1970 cohort. RESULTS: The shifts in the distribution across age appear to be mainly due to changing proportion of those with moderate symptoms, except for midlife (age 42-50) when we observed polarisation in distress- an increase in proportions of people with no symptoms and multiple symptoms. The elevated levels of distress in the 1970 cohort, compared with the 1958 cohort, appeared to be due to an increase in the proportion of individuals with both moderate and high symptoms. For instance, at age 33/34 42.3% endorsed at least two symptoms in the 1970 cohort vs 24.7% in 1958, resulting in a shift in the entire distribution of distress towards the more severe end of the spectrum. CONCLUSIONS: Our study demonstrates the importance of studying not only mean levels of distress over time, but also the underlying shifts in its distribution. Due to the large dispersion of distress scores at any given measurement occasion, understanding the underlying distribution provides a more complete picture of population trends.

A recipe for accurate estimation of lifespan brain trajectories, distinguishing longitudinal and cohort effects.

We address the problem of estimating how different parts of the brain develop and change throughout the lifespan, and how these trajectories are affected by genetic and environmental factors. Estimation of these lifespan trajectories is statistically challenging, since their shapes are typically highly nonlinear, and although true change can only be quantified by longitudinal examinations, as follow-up intervals in neuroimaging studies typically cover less than 10% of the lifespan, use of cross-sectional information is necessary. Linear mixed models (LMMs) and structural equation models (SEMs) commonly used in longitudinal analysis rely on assumptions which are typically not met with lifespan data, in particular when the data consist of observations combined from multiple studies. While LMMs require a priori specification of a polynomial functional form, SEMs do not easily handle data with unstructured time intervals between measurements. Generalized additive mixed models (GAMMs) offer an attractive alternative, and in this paper we propose various ways of formulating GAMMs for estimation of lifespan trajectories of 12 brain regions, using a large longitudinal dataset and realistic simulation experiments. We show that GAMMs are able to more accurately fit lifespan trajectories, distinguish longitudinal and cross-sectional effects, and estimate effects of genetic and environmental exposures. Finally, we discuss and contrast questions related to lifespan research which strictly require repeated measures data and questions which can be answered with a single measurement per participant, and in the latter case, which simplifying assumptions that need to be made. The examples are accompanied with R code, providing a tutorial for researchers interested in using GAMMs.

Older adults incarcerated in state prison: health and quality of life disparities between age cohorts.

OBJECTIVES: This research sought to describe the physical and psychological health and quality of life among older adult men incarcerated in a state prison and to examine the role of age and historical time between age cohorts. METHODS: Survey responses from male respondents incarcerated in a medium-security prison (N = 186) were described using frequencies and descriptive statistics; chi-square and analysis of variance analyses were used to examine differences between age cohorts. RESULTS: The average number of chronic health conditions for the sample was higher than those in similar samples; the proportion of older adults with four or more chronic conditions was 10% higher than the national average for adults age 65 or older. Depression and post-traumatic stress (PTS) symptom severity scores were higher than those found in community-based samples. Significant differences were identified between cohorts regarding physical (number of chronic conditions, F = 12.48, p < .01); functional impairment, F = 4.28, p < .05) and psychological health (PTS symptom severity, F = 3.16, p < .05). CONCLUSION: Policy and practice implications are discussed including the expansion of on- and off-site services for older adults in prisons, enhanced accessibility, and the use of grief counseling and stress management strategies.

Childbirth and Delayed Parkinson's Onset: A Reproducible Nonbiological Artifact of Societal Change.

BACKGROUND: Uncontrolled studies have reported associations between later Parkinson's disease onset in women and a history of giving birth, with age at onset delayed by nearly 3 years per child. We tested this association in two independent data sets, but, as a control to test for nonbiological explanations, also included men with PD. METHODS: We analyzed valid cases from the Parkinson's Progressive Markers Initiative incident sample (145 women, 276 men) and a prevalent sample surveyed by the New Zealand Brain Research Institute (210 women, 394 men). RESULTS: The association was present in both women and men in the Parkinson's Progressive Markers Initiative study, and absent in both in the New Zealand Brain Research Institute study. This is consistent with generational differences common to men and women, which confound with age at onset in incident-dominant samples. CONCLUSIONS: Despite being replicable in certain circumstances, associations between childbirth and later PD onset are an artifact of generational cohort differences. © 2020 International Parkinson and Movement Disorder Society.

Flexible age-period-cohort modelling illustrated using obesity prevalence data.

BACKGROUND: Use of generalized linear models with continuous, non-linear functions for age, period and cohort makes it possible to estimate these effects so they are interpretable, reliable and easily displayed graphically. To demonstrate the methods we use data on the prevalence of obesity among Australian women from two independent data sources obtained using different study designs. METHODS: We used data from two long-running nationally representative studies: seven cross-sectional Australian National Health Surveys conducted between 1995 and 2017-18, each involving 6000-8000 women; and the Australian Longitudinal Study on Women's Health which started in 1996 and involves more than 57,000 women in four age cohorts who are re-surveyed at three-yearly intervals or annually. Age-period-cohort analysis was conducted using generalized linear models with splines to describe non-linear continuous effects. RESULTS: When analysed in the same way both data sets showed similar patterns. Prevalence of obesity increased with age until late middle age and then declined; increased only slightly across surveys; but increased steadily with birth year until the 1960s and then accelerated. CONCLUSIONS: The methods illustrated here make the estimation and visualisation of age, period and cohort effects accessible and interpretable. Regardless of how the data are collected (from repeated cross-sectional surveys or longitudinal cohort studies), it is clear that younger generations of Australian women are becoming heavier at younger ages. Analyses of trends in obesity should include cohort, in addition to age and period, effects in order to focus preventive strategies appropriately.

Life Expectancy: Frequently Used, but Hardly Understood.

Period life expectancy is one of the most used summary indicators for the overall health of a population. Its levels and trends direct health policies, and researchers try to identify the determining risk factors to assess and forecast future developments. The use of period life expectancy is often based on the assumption that it directly reflects the mortality conditions of a certain year. Accordingly, the explanation for changes in life expectancy are typically sought in factors that have an immediate impact on current mortality conditions. It is frequently overlooked, however, that this indicator can also be affected by at least three kinds of effects, in particular in the situation of short-term fluctuations: cohort effects, heterogeneity effects, and tempo effects. We demonstrate their possible impact with the example of the almost Europe-wide decrease in life expectancy in 2015, which caused a series of reports about an upsurge of a health crisis, and we show that the consideration of these effects can lead to different conclusions. Therefore, we want to raise an awareness concerning the sensitivity of life expectancy to sudden changes and the menaces a misled interpretation of this indicator can cause.

Secular rise in economically valuable personality traits.

Although trends in many physical characteristics and cognitive capabilities of modern humans are well-documented, less is known about how personality traits have evolved over time. We analyze data from a standardized personality test administered to 79% of Finnish men born between 1962 and 1976 (n = 419,523) and find steady increases in personality traits that predict higher income in later life. The magnitudes of these trends are similar to the simultaneous increase in cognitive abilities, at 0.2-0.6 SD during the 15-y window. When anchored to earnings, the change in personality traits amounts to a 12% increase. Both personality and cognitive ability have consistent associations with family background, but the trends are similar across groups defined by parental income, parental education, number of siblings, and rural/urban status. Nevertheless, much of the trends in test scores can be attributed to changes in the family background composition, namely 33% for personality and 64% for cognitive ability. These composition effects are mostly due to improvements in parents' education. We conclude that there is a "Flynn effect" for personality that mirrors the original Flynn effect for cognitive ability in magnitude and practical significance but is less driven by compositional changes in family background.

A generalized additive model to disentangle age and diagnosis-specific cohort effects in psychological and behavioral outcomes in people living with HIV: the French cross-sectional ANRS-VESPA2 survey.

BACKGROUND: Unlike their younger counterparts, some of today's older HIV patients were diagnosed before the advent of highly active antiretroviral therapy (HAART). The psychosocial and behavioral outcomes of people living with HIV (PLWH) have been widely studied, and associated factors are well known. However, their evolution both in terms of age and diagnosis-specific cohort effects is not well understood. METHODS: Data from the ANRS-VESPA2 cross-sectional survey, representative of French PLWH, were used to investigate whether psychosocial and behavioral outcomes such as quality of life, need for support and HIV status disclosure, evolve under both the influence of patients' age and diagnosis-specific cohort effects. A semi-parametric generalized additive model (GAM) was employed. The physical and mental components of health-related quality of life, the need for material and moral support, and HIV-status disclosure, constituted our outcomes. RESULTS: Non-linear diagnosis-specific cohort effects were found for physical and mental QoL and HIV-status disclosure. Overall, physical QoL was better in recently diagnosed patients than in those diagnosed in the early 1980s. An increasing influence of diagnosis-specific cohort effects between 1983 and 1995 was observed. No cohort effects were noticeable between 1996 and 2000, while an increasing influence was apparent for patients diagnosed with HIV from 2000 to 2011 (year of study). For mental QoL, the only increase was observed in participants diagnosed with HIV between 1983 and 2000. The relationship between diagnosis-specific cohort effects and HIV status disclosure was negative overall: participants diagnosed after 2000 were much less likely to disclose than those diagnosed before 1995. The effect of age was significantly associated with all outcomes, with a non-linear influence on mental QoL and with the need for material/moral support. CONCLUSIONS: Psychosocial and behavioral outcomes are complex processes which can be explained in different ways by a combination of the clinical and social contexts which PLWH are exposed to at the time of diagnosis, and by developmental characteristics. A greater understanding of these processes could inform healthcare policy-making for specific HIV generations and different HIV age groups.

Rise, stagnation, and rise of Danish women's life expectancy.

Health conditions change from year to year, with a general tendency in many countries for improvement. These conditions also change from one birth cohort to another: some generations suffer more adverse events in childhood, smoke more heavily, eat poorer diets, etc., than generations born earlier or later. Because it is difficult to disentangle period effects from cohort effects, demographers, epidemiologists, actuaries, and other population scientists often disagree about cohort effects' relative importance. In particular, some advocate forecasts of life expectancy based on period trends; others favor forecasts that hinge on cohort differences. We use a combination of age decomposition and exchange of survival probabilities between countries to study the remarkable recent history of female life expectancy in Denmark, a saga of rising, stagnating, and now again rising lifespans. The gap between female life expectancy in Denmark vs. Sweden grew to 3.5 y in the period 1975-2000. When we assumed that Danish women born 1915-1945 had the same survival probabilities as Swedish women, the gap remained small and roughly constant. Hence, the lower Danish life expectancy is caused by these cohorts and is not attributable to period effects.

Work Values in the United States: Age, Period, and Generational Differences.

This article examines how processes of aging, generational shifts, and changes over historical time periods shape differences in work values in the United States. Our analyses of data from the General Social Surveys and the International Social Survey Program show that changes over historical time periods are most consistently responsible for temporal differences in work values. In particular, during recent periods Americans tend to place greater importance on jobs that provide security, high income and opportunities for advancement; this is consistent with a narrative that these job rewards have become more difficult to attain recently and are thus more problematic for workers. Some differences in work values are also attributable to aging or life course processes, especially the greater importance placed on high income during the mid-life years when family responsibilities are generally greatest. By contrast, we find few differences in work values among members of different generations or cohorts. We also find that people from less advantaged social origins and those with greater labor market resources are more likely to value economic rewards.

Direct and indirect effects of early-life environment on lifetime fitness of bighorn ewes.

Cohort effects, when a common environment affects long-term performance, can have a major impact on population dynamics. Very few studies of wild animals have obtained the necessary data to study the mechanisms leading to cohort effects. We exploited 42 years of individual-based data on bighorn sheep to test for causal links between birth density, body mass, age at first reproduction (AFR), longevity and lifetime reproductive success (LRS) using path analysis. Specifically, we investigated whether the effect of early-life environment on lifetime fitness was the result of indirect effects through body mass or direct effects of early-life environment on fitness. Additionally, we evaluated whether the effects of early-life environment were dependant on the environment experienced during adulthood. Contrary to expectation, the effect on LRS mediated through body mass was weak compared to the effects found via a delay in AFR, reduced longevity and the direct effect of birth density. Birth density also had an important indirect effect on LRS through reduced longevity, but only when adult density was high. Our results show that the potential long-term consequences of a harsh early-life environment on fitness are likely to be underestimated if investigations are limited to body mass instead of fitness at several life stages, or if the interactions between past and present environment are ignored.