Title:
Causal Inference Approaches for Understanding the Social Determinants of Substance Abuse and Depression in the 21st Century: The Opioid Epidemic and the Great Recession
Author:
Samuel Swift
Date:
2019
Executive Summary:
The great recession and the opioid epidemic are two defining public health events of the 21st century. Within the context of these two events, the 21st century has been marked by increases in mortality due to suicide, alcohol misuse, and drug overdose among Americans, and especially among white Americans, warranting further epidemiological investigation. For example, in recent years a black-white disparity in opioid pain reliever (OPR) misuse has emerged such that white Americans are more likely to suffer opioid overdoses or opioid related hospitalizations than black Americans. There is evidence to support that much of the opioid epidemic is related to overprescribing of OPR medications, and that whites are more likely to be prescribed these medications than blacks. In aim 1 of this dissertation I build on prior work which suggests that discrimination in medical settings may actually be protective against iatrogenic outcomes in medicine. I postulate that discrimination could result in less prescribing of OPR medications for blacks and thus a lower risk of OPR misuse. While most epidemiologic studies rely on a self-reported measure of OPR misuse, these measures are often an underreport of true OPR misuse when compared with gold standard measures. Aim 2 of this dissertation examines the possible bias introduced to the observed associations of aim 1 which uses self-reported OPR misuse. Finally, in aim 3 of this dissertation, I examined the great recession of 2008, another defining public health event of the 21st century which resulted in shocks to financial wellbeing that were felt by persons worldwide, and its effect on drug misuse, alcohol misuse, and depression. During the great recession in the United States shocks to financial wellbeing such as unemployment drastically increased, while median income and household assets decreased. While shocks to financial wellbeing have been shown to be associated with increased depressive symptoms, the associations between these shocks and alcohol and drug use behaviors are less understood.
As a whole, this dissertation aims to better understand how the opioid epidemic and the great recession have played out with regards to the social axes of class and race, using causal inference methods. All three of my aims were evaluated using the Coronary Artery Risk Development In young Adults study (CARDIA) which is an ongoing prospective longitudinal cohort study of black and white adults who were ages 18 to 30 when they were enrolled in the study in 1985. This sample is ideal for these dissertation aims because the participants were adults during the opioid epidemic and at the peak of their working years during great recession of 2008 (mean ages 45-50). Additionally, this study collects rich data on discrimination, as well as socioeconomic data related to employment, income, debts and assets.
In aim 1 of the dissertation, I first assess the black vs white disparity in OPR misuse, and then I evaluate whether racial discrimination in medical care settings mediates this disparity. In my framework, race is the exposure, racial discrimination in a medical care setting is the mediator, and OPR misuse is the outcome. I used causal mediation analysis to compute the total effects and controlled direct effects, which are as follows: the total effect (TE) is the effect of race on OPR misuse, adjusted for measured confounders; and the controlled direct effect (CDE) is the effect of race on OPR misuse when discrimination is set at the same level for all participants, adjusted for measured confounders. I calculated inverse probability treatment weights (IPTW) for discrimination to address confounders that also act as mediators. I found that black participants were more likely to report discrimination in a medical setting (20.3% vs 0.9%) and less likely to report OPR misuse (OR=0.71, 95% CI= 0.55, 0.93), in the total effect model. In my final model adjusting for the IPTW of the confounding/mediating variables, my controlled direct effect suggests that when everyone is set to being not discriminated against, the disparity is wider such that black persons are further less likely to report OPR misuse (OR=0.63, 95% CI=0.45, 0.89) compared to their white counterparts. These findings suggest racial discrimination in medical settings is a risk factor for OPR misuse rather than protective.
In aim 2 of the dissertation, I evaluate how potential measurement error in discrimination could have influenced the findings of aim 1. Validation studies that compare self-reported misuse with urine or hair analysis show that self-reporting of OPR misuse is usually underreported, often at very low levels of sensitivity. In this aim I use probabilistic bias analysis applying different values of the sensitivity of self-reported OPR misuse to the observed bivariate relationships between race and OPR (from aim 1). Assuming a non-differential misclassification and a sensitivity of 75% among blacks and 90% among whites, which is higher than that found in validation studies among high risk OPR users, our aim 1 black-white disparity (i.e. race – OPR association) reflects an overestimate of the true disparity (bias corrected OR =0.94, 95% CI =0.91, 0.97) vs. observed OR=0.73, 95% CI= 0.57, 0.93). When we change the sensitivity among blacks to a very low level (50%) with the white sensitivity at 75%, the observed black-white disparity would actually flip (bias corrected OR= 2.13, 95% CI=1.51, 3.30 vs. observed OR= 0.73, 95% CI= 0.57, 0.93).
In aim 3 of the dissertation, I use a fixed effects design to examine how within person change in financial well-being at time of the great recession influenced depressive symptoms, alcohol and drug misuse. I consider three types of shocks to financial wellbeing: unemployment, drops in income, and a shift in the ratio of household debts to assets. In my final models, I found that unemployment was associated with an increase in depressive symptoms (β=2.0, 95% CI=0.6, 3.3). A shift in debts to assets ratio was also associated with an increase in depressive symptoms (β=1.3 95% CI= 0.1, 2.5) but a decrease in daily mL of alcohol consumed (β=-4.1, 95% CI= -6.7, -1.5). While the associations between shocks to financial wellbeing and drug misuse were not statistically significant, the odds ratios suggest that these shocks were a possible risk for drug misuse.
Taken together, these three aims illustrate methodological approaches to evaluating research questions pertaining to some of the most currently pressing public health issues. The results of aim 1 suggest that racial discrimination in a medical setting is a risk factor for OPR misuse rather than being protective, and thus could not explain the seen black-white disparity in OPR misuse. This finding is consistent with previous literature on discrimination and substance misuse among other health outcomes. Further research is needed to investigate the mechanisms behind the black–white disparity in OPR misuse, including the source of OPR medications. In aim 2 I found that differential misclassification of OPR misuse at levels similar to those found in validation studies has the potential to significantly bias observed associations. In aim 3 I found that unemployment and shifts in debts to assets ratio during the great recession increased depressive symptoms. A shift in debts to assets ratio also decreased the total mL of alcohol consumed. These results highlight the complex relationship between recessions and health and the importance of examining different types recession related shocks.
