Measuring occupation as the longest occupation is an approach that helps to capture the accumulation of the potential health impact of work and minimize the endogeneity between occupation and health among older adults. We find substantial variation in self-rated health across longest occupation at baseline in this group of middle-age and older adults. As expected, when we control for additional variables that are related to occupations (e.g., income), the magnitudes of the intercept coefficients on occupation decline.
Contrary to our expectations, we do not find any significant impact of occupation on changes in health over time, nor do the slope coefficients on occupation change as additional variables are included. That is, the occupation-related differences found at baseline are durable and persist as individuals age, even though some individuals leave their longest occupations because of job changes or retirement. Although the trajectory results show that disparities do not widen over the study period, it is striking that the occupation-related disparities in health persist, given that a considerable share (40%) of sample members transition out of their longest occupation over the study period. Across the survey waves, at baseline 58% of the sample has a current occupation that is the same as their longest occupation, declining to 34% by Wave 4 and 19% by Wave 7. Our results are consistent with a life course view of social determinants of health; health problems accumulate over the lifetime and are systematically different by occupation, but differences appear to be stable in older ages.
Our results are also consistent with, and extend, prior research that finds baseline differences that do not widen over time. For example, Lindenberger and Baltes (1997)
find that while there are baseline differences in intellectual capacity by socioeconomic status (SES), the decline in this capacity is equal by SES, thus preserving the baseline differences across age categories. An 11-year follow-up of the Whitehall II study (Ferrie et al., 2002
; Marmot et al., 1997
) found no change in the physical health disparity observed at baseline, although mental health disparities widened.
By studying civil servants, the Whitehall studies provide particularly compelling evidence that a gradient exists even among a relatively advantaged population. However, it is also important to examine occupation-related differences in health in a representative population and within the age range when potential cumulative effects of employment on health may be more likely to be experienced. Our study examines differences across a representative middle age and older population that reflects the range of occupational experiences in the United States. We also show that these differences persist in the full model that controls for education, income, and wealth, indicating that occupation has a separate effect on health beyond traditional measures of SES. Other studies, including Whitehall, do not control for all of these factors.
There are limitations to this study. As with all observational studies, there is the possibility of omitted variable bias. Nevertheless, the advantages of the HRS, particularly its national sample of older workers and breadth of covariate data, may outweigh shortcomings related to the omission of potentially relevant factors. Another matter is heterogeneity within occupation classes. A rather small set of occupations is a practical requirement for the type of analysis undertaken in this study. However, with such a defined set, there is likely heterogeneity within the occupation categories. Moreover, with a small number of occupational classes in which at least three categories (sales, clerical and administrative, and service) potentially contain a mix of white- and blue-collar workers, our results may reproduce the finding that industrial workers have poorer health than workers in white-collar occupations.
Another possible limitation is that we do not consider time-dependent covariates or mediators such as changes in health habits or employment status. However, changes in health habits, retirement, and other employment status transitions can be as much a consequence of change in health as a mediator of occupation effects on health. For example, highly paid occupations could allow workers to retire relatively early, which in turn could improve health, whereas physically demanding occupations could lead to declining health, which in turn can lead to early retirement. Disentangling these two possible causal chains is a challenging statistical modeling problem that is beyond the scope of this short research note. Our analyses are focused on the specific question of occupation effects when controlling for baseline levels of potential confounding factors, thus avoiding the endogeneity of changes in predictors and health.
We took multiple steps to address dropout, which strengthen the findings of the study. Use of longest occupation allows us to examine nonworking individuals. Individuals with at least one observation are included in our sample even if they drop out or die later in the study period. In so doing, we maximize statistical power and minimize the potential of bias due to sample restriction. In addition, we control for dropout due to death and other reasons by including additional indicator variables in our intercept and slope predictions. Thus, we are able to ascertain that subjects who drop out have poorer health at baseline and faster deterioration over time. Sensitivity analyses show that our results are unlikely to be significantly affected by dropout and death.
In conclusion, our analysis assessing the relationship between longest occupation and health shows that occupation has an effect on health, even after controlling for measures relating to occupation, including education, income, and health insurance. The lasting effect of longest occupation on health even after change in job or retirement indicates the durability of the impact of longest occupation. The persistence of occupation-related health disparities, even when people are no longer working, suggests that longest occupation is a phenomenon worthy of further study.