Misunderstandings, mischaracterizations, and the problematic choice of a specific instance in which the IE should never be applied

Beliefs about harms of cigarette smoking among Norwegian adults born from 1899 to 1969. Do variations across education, smoking status and sex mirror the decline in smoking?

Background and aim

Smoking is one of the most important causes of socioeconomic disparities in morbidity and mortality. The aim of this study was to examine if beliefs about harms of smoking differed across gender, smoking status and education among Norwegian adults born between 1899 and 1969.

Methods

Using data from a nationally representative survey of smoking habits and a multinomial logit/negative binomial two-stage hurdle model design, we examined (first hurdle) the associations between birth cohort, gender, education and smoking status and four beliefs about cigarette smoking: i) smoking is not harmful, ii) do not know if smoking is harmful, iii) any number of cigarettes per day (CPD) is harmful and iv) smoking more than a given nonzero number of CPD is harmful, and (second hurdle) the predicted number of CPD that could be smoked without causing harm (from outcome iv).

Results

The probability of believing that smoking was not harmful was close to zero, regardless of birth cohort, sex, education and smoking status. The probability of not knowing if smoking was harmful decreased from around 0.7 to almost zero across cohorts. The probability of believing that smoking more than zero CPD was harmful increased from less than 0.1 to around 0.7, while the probability of believing that there is some safe level of smoking increased with cohorts born from 1900 to 1930 before declining. Respondents with primary/secondary education consistently believed smoking to be less harmful compared to respondents with tertiary education, but cohort trajectories were similar.

Discussion

The similar birth cohort trajectories in beliefs about the harms of smoking do not support the idea that Norwegian adults with lower education has had qualitatively different beliefs about the harmfulness of smoking compared to those with higher education. The persistent and large socioeconomic gradient is likely a result of other factors.

Getting a Grip on Secular Changes: Age-Period-Cohort modeling of grip strength in the English Longitudinal Study of Ageing

BACKGROUND

Grip strength is a popular and valuable measure in studies of physical functional capabilities in old-age. The influence of historical trends and differential period-specific exposures can complicate the interpretation of biomarkers of aging and health and requires careful analysis and interpretation of ageing, birth cohort, and period effects. The current study evaluates the effects of aging, period, and cohort on grip strength in a population of adults and older adults.

METHODS

We use >27,000 observations for individuals ≥50 years of age, born in approximately 1910-1960, from the English Longitudinal Study of Aging to examine a variety of multilevel and cross-classified modeling approaches to evaluate age, period, and cohort effects. Our results extended Hierarchical Age Period Cohort modeling and compared our results with a set of nine sub-models with explicit assumptions to determine the most reliable modeling approach.

RESULTS

Findings suggest grip strength is primarily related to age, with minimal evidence of either period and/or cohort effects. Each year's increase in a person's age was associated with a 0.40-kilogram decrease in grip strength, though this decline differs by gender.

CONCLUSIONS

We conclude that as a population ages, grip strength declines at a systematic and predictable rate equal to -0.40-kilograms per year (approximately -.50-kg for men and -.30-kg for women) in residents of England aged 50 and older. Age-effects were predominant and most consistent across methodologies. While there was some evidence for cohort effects, such effects were minimal and therefore indicative that grip strength is a consistent physiological biomarker of aging.

Clarifying assumptions in age-period-cohort analyses and validating results

BACKGROUND

Age-period-cohort (APC) models are often used to decompose health trends into period- and cohort-based sources, but their use in epidemiology and population sciences remains contentious. Central to the contention are researchers' failures to 1) clearly state their analytic assumptions and/or 2) thoroughly evaluate model results. These failures often produce varying conclusions across APC studies and generate confusion about APC methods. Consequently, scholarly exchanges about APC methods usually result in strong disagreements that rarely offer practical advice to users or readers of APC methods.

METHODS

We use research guidelines to help practitioners of APC methods articulate their analytic assumptions and validate their results. To demonstrate the usefulness of the guidelines, we apply them to a 2015 American Journal of Epidemiology study about trends in black-white differences in U.S. heart disease mortality.

RESULTS

The application of the guidelines highlights two important findings. On the one hand, some APC methods produce inconsistent results that are highly sensitive to researcher manipulation. On the other hand, other APC methods estimate results that are robust to researcher manipulation and consistent across APC models.

CONCLUSIONS

The exercise shows the simplicity and effectiveness of the guidelines in resolving disagreements over APC results. The cautious use of APC models can generate results that are consistent across methods and robust to researcher manipulation. If followed, the guidelines can likely reduce the chance of publishing variable and conflicting results across APC studies.

Effects of Emotions on Sexual Behavior in Men with and without Hypersexuality

The association between positive and negative affect and sexual behavior in 39 MSM with and without hypersexuality (HS) was explored using ecological momentary assessment. Participants reported their current positive and negative affect three times per day and their sexual behavior each morning and evening. The relationship between affect and sexual behavior differed between men with or without HS. In those with HS, the timing of and interactions between experienced affect differentially predicted types of sexual behavior, indicating differing mechanisms driving partnered sexual behavior and masturbation. These findings lend support to conceptualizing HS behavior as a coping strategy for affective arousal.

Cohort-based income gradients in obesity among U.S. adults

OBJECTIVES

No studies have focused on socioeconomic disparities in obesity within and between cohorts. Our objectives were to examine income gradients in obesity between birth-cohorts (inter-cohort variations) and within each birth-cohort (intra-cohort variations) by gender and race/ethnicity.

METHODS

Our sample includes 56,820 white and black adults from pooled, cross-sectional National Health and Nutrition Examination Surveys (1971-2012). We fit a series of logistic hierarchical Age-Period-Cohort models to control for the effects of age and period, simultaneously. Predicted probabilities of obesity by poverty-to-income ratio were estimated and graphed for 5-year cohort groups from 1901-1990. We also stratified this relationship for four gender and racial/ethnic subgroups.

RESULTS

Obesity disparities due to income were weaker for post-World War I and II generations, specifically the mid-1920s and the mid-1940s to 1950s cohorts, than for other cohorts. In contrast, we found greater income gradients in obesity among cohorts from the 1930s to mid-1940s and mid-1960s to 1970s. Moreover, obesity disparities due to income across cohorts vary markedly by gender and race/ethnicity. White women with higher income consistently exhibited a lower likelihood of obesity than those with lower income since early 1900s cohorts; whereas, black men with higher income exhibited higher risks of obesity than those with lower income in most cohorts.

CONCLUSIONS

Our findings suggest that strategies that address race and/or gender inequalities in obesity should be cognizant of significant historical factors that may be unique to cohorts. Period-based approaches that ignore life-course experiences captured in significant cohort-based experiences may limit the utility of policies and interventions.

Three Dimensions of Change in School Segregation: A Grade-Period-Cohort Analysis

This study uses the first age-period-cohort (APC) analysis of segregation to examine changes in U.S. public school segregation from 1999-2000 to 2013-2014. APC analyses disentangle distinct sources of change in segregation, and they account for grade effects that could distort temporal trends if grade distributions change over time. Findings indicate that grade effects are substantial, drastically reducing segregation at the transition to middle school and further at the transition to high school. These grade effects do not substantially distort the analysis of recent trends, however, because grade distributions were sufficiently stable. Black-white segregation was stagnant overall, while Hispanic-white segregation declined modestly. In both cases, declines across periods were offset by increases across cohorts. Further analyses reveal variation in these trends across metropolitan and nonmetropolitan areas, regions, and areas with different histories of desegregation policy.

The hierarchical age-period-cohort model: Why does it find the results that it finds?

It is claimed the hierarchical-age–period–cohort (HAPC) model solves the age–period–cohort (APC) identification problem. However, this is debateable; simulations show situations where the model produces incorrect results, countered by proponents of the model arguing those simulations are not relevant to real-life scenarios. This paper moves beyond questioning whether the HAPC model works, to why it produces the results it does. We argue HAPC estimates are the result not of the distinctive substantive APC processes occurring in the dataset, but are primarily an artefact of the data structure—that is, the way the data has been collected. Were the data collected differently, the results produced would be different. This is illustrated both with simulations and real data, the latter by taking a variety of samples from the National Health Interview Survey (NHIS) data used by Reither et al. (Soc Sci Med 69(10):1439–1448, 2009) in their HAPC study of obesity. When a sample based on a small range of cohorts is taken, such that the period range is much greater than the cohort range, the results produced are very different to those produced when cohort groups span a much wider range than periods, as is structurally the case with repeated cross-sectional data. The paper also addresses the latest defence of the HAPC model by its proponents (Reither et al. in Soc Sci Med 145:125–128, 2015a). The results lend further support to the view that the HAPC model is not able to accurately discern APC effects, and should be used with caution when there appear to be period or cohort near-linear trends.

HOW THE U.S. PRISON BOOM HAS CHANGED THE AGE DISTRIBUTION OF THE PRISON POPULATION

This article provides a demographic exposition of the changes in the U.S prison population during the period of mass incarceration that began in the late twentieth century. By drawing on data from the Survey of Inmates in State Correctional Facilities (1974-2004) for inmates 17-72 years of age (N = 336), we show that the age distribution shifted upward dramatically: Only 16 percent of the state prison population was 40 years old or older in 1974; by 2004, this percentage had doubled to 33 percent with the median age of prisoners rising from 27 to 34 years old. By using an estimable function approach, we find that the change in the age distribution of the prison population is primarily a cohort effect that is driven by the "enhanced" penal careers of the cohorts who hit young adulthood-the prime age of both crime and incarceration-when substance use was at its peak. Period-specific factors (e.g., proclivity for punishment and incidence of offense) do matter, but they seem to play out more across the life cycles of persons most affected in young adulthood (cohort effects) than across all age groups at one point in time (period effects).

The Non-uniqueness Property of the Intrinsic Estimator in APC Models

This article explores an important property of the intrinsic estimator that has received no attention in literature: the age, period, and cohort estimates of the intrinsic estimator are not unique but vary with the parameterization and reference categories chosen for these variables. We give a formal proof of the non-uniqueness property for effect coding and dummy variable coding. Using data on female mortality in the United States over the years 1960-1999, we show that the variation in the results obtained for different parameterizations and reference categories is substantial and leads to contradictory conclusions. We conclude that the non-uniqueness property is a new argument for not routinely applying the intrinsic estimator.

Changes in mortality due to major alcohol-related diseases in four Nordic countries, France and Germany between 1980 and 2009: a comparative age-period-cohort analysis

AIMS

To investigate age, period and cohort effects on time trends of alcohol-related mortality in countries with different drinking habits and alcohol policies.

DESIGN AND SETTING

Age-period-cohort (APC) analyses on alcohol-related mortality were conducted in Denmark, Finland, Norway, Sweden, France and Germany.

PARTICIPANTS

Cases included alcohol-related deaths in the age range 20-84 years between 1980 and 2009.

MEASUREMENTS

Mortality data were taken from national causes of death registries and covered the ICD codes alcoholic psychosis, alcohol use disorders, alcoholic liver disease and toxic effect of alcohol.

FINDINGS

In all countries changes across age, period and cohort were found to be significant for both genders [effect value with confidence interval (CI) shown in Supporting information, Table S1]. Period effects pointed to an increase in alcohol-related mortality in Denmark, Finland and Germany and a slightly decreasing trend in Sweden, while in Norway an inverse U-shaped curve and in France a U-shaped curve was found. Compared with the cohorts born before 1960, the risk of alcohol-related mortality declined substantially in cohorts born in the 1960s and later. Pairwise between-country comparisons revealed more statistically significant differences for period (P < 0.001 for all 15 comparisons by gender) than for age [P < 0.001 in seven (men) and four (women) of 15 comparisons] or cohort [P < 0.01 in two (men) and three (women) of 15 comparisons].

CONCLUSIONS

Strong period effects suggest that temporal changes in alcohol-related mortality in Denmark, Finland, Norway, Sweden, France and Germany between 1980 and 2009 were related to secular differences affecting the whole population and that these effects differed across countries.

Age, period, and cohort effects in motor vehicle mortality in the United States, 1980-2010: the role of sex, alcohol involvement, and position in vehicle

INTRODUCTION

Although substantive declines in motor vehicle fatalities in 1980-2010 have been observed, declines by position in the vehicle and alcohol involvement have not been well elucidated.

METHOD

Analyses of FARS data use the Intrinsic Estimator (IE) to produce estimates of all age, period, and cohort effects simultaneously by position in the car and by alcohol involvement.

RESULTS

Declines in MVC deaths by position in the car vary for men and women by age and cohort over time. Cohorts born before 1970 had higher risks than those born later. Analyses using proxy indicators of alcohol involvement found the highest risks for those aged 16-24. By period, these risks declined more rapidly than non- alcohol related traffic fatalities.

CONCLUSION

Changes in risk patterns are consistent with evidence regarding the contributions of new technologies and public policy efforts to reduce fatalities, but gains have not been shared evenly by sex or position in the car.

PRACTICAL APPLICATIONS

Greater attention is needed in reducing deaths among older drivers and pedestrians. Gender differences should be addressed in prevention efforts aimed at reducing MVCs due to alcohol involvement.

Should age-period-cohort studies return to the methodologies of the 1970s?

Social scientists have recognized the importance of age-period-cohort (APC) models for half a century, but have spent much of this time mired in debates about the feasibility of APC methods. Recently, a new class of APC methods based on modern statistical knowledge has emerged, offering potential solutions. In 2009, Reither, Hauser and Yang used one of these new methods - hierarchical APC (HAPC) modeling - to study how birth cohorts may have contributed to the U.S. obesity epidemic. They found that recent birth cohorts experience higher odds of obesity than their predecessors, but that ubiquitous period-based changes are primarily responsible for the rising prevalence of obesity. Although these findings have been replicated elsewhere, recent commentaries by Bell and Jones call them into question - along with the new class of APC methods. Specifically, Bell and Jones claim that new APC methods do not adequately address model identification and suggest that "solid theory" is often sufficient to remove one of the three temporal dimensions from empirical consideration. They also present a series of simulation models that purportedly show how the HAPC models estimated by Reither et al. (2009) could have produced misleading results. However, these simulation models rest on assumptions that there were no period effects, and associations between period and cohort variables and the outcome were perfectly linear. Those are conditions under which APC models should never be used. Under more tenable assumptions, our own simulations show that HAPC methods perform well, both in recovering the main findings presented by Reither et al. (2009) and the results reported by Bell and Jones. We also respond to critiques about model identification and theoretically-imposed constraints, finding little pragmatic support for such arguments. We conclude by encouraging social scientists to move beyond the debates of the 1970s and toward a deeper appreciation for modern APC methodologies.

An age-period-cohort analysis of cancer incidence among the oldest old, Utah 1973-2002

We used age-period-cohort (APC) analyses to describe the simultaneous effects of age, period, and cohort on cancer incidence rates in an attempt to understand the population dynamics underlying their patterns among those aged 85+. Data from the Utah Cancer Registry (UCR), the US Census, the National Center for Health Statistics (NCHS), and the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) programme were used to generate age-specific estimates of cancer incidence at ages 65-99 from 1973 to 2002 for Utah. Our results showed increasing cancer incidence rates up to the 85-89 age group followed by declines at ages 90-99 when not confounded by the separate influences of period and cohort effects. We found significant period and cohort effects, suggesting the role of environmental mechanisms in cancer incidence trends between the ages of 85 and 100.