metadata: authors: 0: author: Cawley,John Horan
1: author: De Walque,Damien B. C. M.
2: author: Grossman,Daniel
count: United States,Vietnam
docna: 0: docna: Effect of stress on later-life health :
            evidence from the Vietnam war draft
docty: Policy Research Working Paper
subtopic: Conflict and Fragile States,Health Care Services Industry,Disease Control & Prevention,Educational Sciences,Armed Conflict
teratopic: Health, Nutrition and Population
abstracts: cdata!: A substantial literature has examined
            the impact of stress during the early stages of life on
            later-life health. This paper contributes to that literature
            by examining the later-life health impact of stress during
            adolescence and early adulthood, using a novel proxy for
            stress: risk of military induction in the United States
            during the Vietnam War. The paper estimates that a 10
            percentage point (2 standard deviation) increase in
            induction risk in young adulthood is associated with a 1.5
            percentage point (8 percent) increase in the probability of
            being obese, and a 1 percentage point (10 percent) increase
            in the probability of being in fair or poor health later in
            life. These findings do not appear to be due to cohort
            effects; the associations exist only for men who did not
            serve in the war, and are not present for women or men who
            did serve. These findings add to the evidence on the lasting
            consequences of stress, and indicate that induction risk
            during the Vietnam War may, in certain contexts, be an
            invalid instrument for education or marriage, because it
            appears to have a direct impact on health.
geo_reg_key: 119228,517198,517191
repnme: repnme: Effect of stress on later-life health :
            evidence from the Vietnam war draft
display_title: Effect of stress on later-life
            health : evidence from the Vietnam war draft
listing_relative_url: /research/2017/05/27470674/effect-stress-later-life-health-evidence-vietnam-war-draft
topicv3: Obesity m1326327 1435,Education m1327048 470,Political Violence and War m1327310 2462,Health m1504661 3480,Military m1505651 3036
publishtoextweb_dt: 2017-05-16T00:00:00Z
historic_topic: Health, Nutrition and Population
no_of_pages: 54
author_keys: 0: author_key: 1260170
1: author_key: 687876
model_extractions: WPS8063 Policy Research Working Paper 8063 Effect of Stress on Later-Life Health Evidence from the Vietnam War Draft _John Cawley Damien de Walque Daniel Grossman_ Development Research Group Human Development and Public Services Team May 2017
Policy Research Working Paper 8063

# **Abstract**

A substantial literature has examined the impact of stress during the early stages of life on later-life health. This paper contributes to that literature by examining the later-life health impact of stress during adolescence and early adulthood, using a novel proxy for stress: risk of military induction in the United States during the Vietnam War. The paper estimates that a 10 percentage point (2 standard deviation) increase in induction risk in young adulthood is associated with a 1.5 percentage point (8 percent) increase in the probability of being obese, and a 1 percentage point (10 percent) increase in the probability of being in fair or poor health later in life. These findings do not appear to be due to cohort effects; the associations exist only for men who did not serve in the war, and are not present for women or men who did serve. These findings add to the evidence on the lasting consequences of stress, and indicate that induction risk during the Vietnam War may, in certain contexts, be an invalid instrument for education or marriage, because it appears to have a direct impact on health.

This paper is a product of the Human Development and Public Services Team, Development Research Group. It is part of a larger effort by the World Bank to provide open access to its research and make a contribution to development policy discussions around the world. Policy Research Working Papers are also posted on the Web at http://econ.worldbank.org. The authors may be contacted at at johncawley@cornell.edu; ddewalque@worldbank.org and daniel.grossman@mail.wvu.edu .

_The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent._ Produced by the Research Support Team
**<mark>Effect of Stress on Later-Life Health: Evidence from the Vietnam War Draft</mark>**<sup>**1**</sup>

<mark>John Cawley, Cornell University Damien de Walque, Development Research Group, The World Bank Daniel Grossman, West Virginia University</mark><sup>2</sup>

**Keywords:** Stress, Obesity, Long-term Health Outcomes, Vietnam War Draft **JEL codes: I12, I18, I31**

> 1 Cawley gratefully acknowledges an Investigator Award in Health Policy Research from the Robert Wood Johnson Foundation. We thank Adam Wagstaff and participants at European Health Economic Association Congress in Hamburg for helpful comments. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the World Bank, its Executive Directors, or the countries they represent.

> 2 Corresponding Author: Daniel Grossman, Business and Economics Building, West Virginia University, Morgantown, WV 26506-6025, email: daniel.grossman@mail.wvu.edu.
# **1. Introduction**

Many studies have estimated the long-term consequences of in utero exposure to stress and illness (see e.g. Almond and Currie 2011; Aizer et al., 2016). In contrast, the long-term consequences of stress experienced during late adolescence and early adulthood has received relatively little attention, despite that this is an important developmental time for the brain (NIMH, 2011; Kaestner and Yarnoff 2011, Dahl 2004).

In this paper, we estimate the long-term health consequences of stress during adolescence and early adulthood. We use a novel measure of stress: the risk of being inducted into the military during the Vietnam War.<sup>3</sup> We exploit the substantial year-to-year variation in induction risk between 1955 (after the Korean War) and 1973 (when the US switched to an all-volunteer force) that resulted from both changes in demand for military manpower and changes in which ages were eligible for the draft. We focus on the entire period of the war (1955-72), not just the period of the draft lottery (1970-72), which is important because the pre-lottery years were a particularly morbid and lethal time for American soldiers.<sup>4</sup> We argue that the prolonged uncertainty about whether one would be conscripted into military service between the ages of 181⁄2 and 26 caused large amounts of stress on young men. Highly publicized calls for increased troop levels in Vietnam and increasingly large numbers of U.S. servicemen being killed or wounded were well documented by media outlets, which made this risk particularly salient.

> 3 “The Vietnam War” is the most common name given in English to the conflict that took place in Vietnam between 1955 and 1975. It is the term we are using in this paper. The conflict is also called the Second Indochina War and in Vietnam it is commonly known as the “Resistance War against America”.

> 4 Over 80 percent of US casualties were suffered before the first draft lottery occurred on December 1, 1969. Public outcry and a shift from explicitly pro-US government media coverage to a more nuanced approach covering public dissent and occasionally showing explicit, disturbing war images suggest the salience to risk of being inducted persisted during the draft lottery years as well (The U.S. National Archives and Records Administration, 2013, Griffin, 2010, Hallin, 1984).

2
We focus on men who did not serve in the military during the Vietnam War; for these men, we can accurately estimate their lifetime exposure to induction risk. For men who did serve, we do not know their induction risk because we do not know at what age they were inducted, nor whether they volunteered or were drafted. Moreover, those who served faced much greater stress (e.g., due to combat) that is unrelated to their induction risk and is unquantifiable by us.

We find consistent evidence that early adult stress, as measured by induction risk, is associated with worse later-life health. A 10 percentage point increase in induction risk, which is a 2 standard deviation increase, is associated with a 0.2 unit (0.08%) increase in BMI, a 1.5 percentage point (1%) increase in the probability of being obese, a 1 percentage point (1%) increase in the probability of being in fair or poor health and a 2 percentage point (0.3%) decrease in the probability of being in very good or excellent health. This does not appear to be due to cohort effects or other trends; these associations exist only for men who did not serve in the military during the Vietnam War, not for men who did serve in the military or women.

In Section 2, we review the relevant literature. Section 3 describes the data and in Section 4 we describe our methods. We present our results in Section 5 before concluding in Section 6.

# **2. Literature Review**

# **2.1 Early-Life Stress and Later-Life Health**

A large and growing literature in economics estimates the effect of early life stressors on a wide variety of later-life outcomes, including educational attainment, earnings, and health (see Almond and Currie 2011; Aizer et al., 2016; Camacho, 2008). This literature generally focuses on stressors in utero or during infancy, but other research, examining the long-term effects of leaving school during a recession on later life health, has found significant negative effects on health for adult men (Maclean 2013, Maclean et al. 2016). Another line of research seeks to 3
document the impact of extreme events such as conflicts, ethnic violence or natural disasters on the mental health and stress levels of adolescents and young adults (Blattman and Annan 2010; Do and Iyer 2010; Fernando, Miller and Berger 2010; Shemyakina and Plagnol 2013). This literature, which focuses more on developing countries, measures variations in stress levels and from there hypothesizes detrimental consequences in the future, but because it often lacks a long enough time horizon, it rarely allows assessing the impact of stress on later-life health.

# **2.2. Effects of Induction Risk on Health**

Our proxy for stress is lifetime induction risk during the Vietnam War; we say “lifetime risk” because the ages at which one was eligible for induction ranged over time from one year to seven and a half years. The armed forces induction system may affect health through at least three routes: 1) increased stress caused by the risk of serving in the armed forces; 2) military service; 3) draft-avoidance behaviors such as attending college or getting married to receive military exemptions. Below, we discuss each of these possible mechanisms.

# **2.2.1 Clinical Effects of Stress on Bodily Function and Health**

Exposure to risk of being inducted into the military during the Vietnam War caused great uncertainty about one’s future and may have increased individuals’ stress levels for long periods of time. For most of the war, men were at risk of being drafted for seven and a half years: from 18.5 to 26 (see Table 1).

Chronic or repeated stress can lead to harmful health effects (Schneiderman et al. 2005, Lupien et al. 2009; Gardner and Oswald, 2004). Individual response patterns vary based on early life experiences, the age at which stress occurs, coping mechanisms, the type and persistence of stressors, genetic endowments, and personal environment and constitution (Schneiderman et al. 2005, Lupien et al. 2009). The pathways through which stress may affect health are complex, 4
including psychological and biochemical responses, as well as behavioral changes that may be initiated through these channels (Schneiderman et al. 2005).

Exposure to stress leads to biological responses from the nervous, cardiovascular, endocrine, and immune systems (Schneiderman et al. 2005). Stressors lead to the release of hormones such as epinephrine and cortisol, which increase sources of energy through higher blood sugar and the breaking down of fats into useable energy (Schneiderman et al. 2005, Sapolsky et al. 2000). The body diverts this energy to tissues that become more active during stress (skeletal muscles and brain) and away from less critical activities like eating, growth, and sexual activity (Schneiderman et al. 2005). This temporarily increases blood pressure through increased heart rate and stroke volume (the amount of blood pumped with each beat). Chronic mobilization of these processes is associated with high blood pressure, cardiac hypertrophy (the thickening of the heart muscle, which reduces the heart chamber size), damaged arteries and plaque formation, suppressed immunity including atrophied wound healing, slower surgery recovery, higher susceptibility to viruses including upper respiratory infections, worse antibody response to vaccines, and increased inflammation which can exacerbate many of the aforementioned conditions (Schneiderman et al. 2005, Sapolsky et al. 2000). Importantly, stress can lead to psychological problems like anxiety and depression, which are associated with sleep problems, substance abuse, heavier cigarette consumption, and higher alcohol consumption (Schneiderman et al. 2005).

Additionally, stress affects individuals’ eating patterns. Jackson et al. (2017) find chronic stress, as measured by hair cortisol levels, to be associated with numerous measures of increased body weight, including persistence of obesity. A potential pathway through which stress affects obesity is by diminishing an individual’s self-control leading to non-utility maximizing, 5
potentially impulsive food decisions like eating more energy-dense, high-calorie foods (Ruhm 2012, Torres and Nowson 2007).

# **2.2.2. The Effects of Military Service on Later-Life Outcomes**

Researchers have studied the effect of military service on labor market outcomes (Angrist 1990), education outcomes (Card and Lemieux 2001), and violent crimes (Lindo and Stoecker 2014). See Dobkin and Shabani (2009) for a discussion of the health effects of military service, and Gimbel and Booth (1996) for a discussion of stress among veterans. However, we focus on men who did not serve in the military, so the mechanism of actual military service is not relevant.

# **2.2.3 The Effects of Draft Avoidance Behaviors on Later-life Outcomes**

For certain periods of the Vietnam War, otherwise draft-eligible men could receive deferments for being enrolled in college; for this reason, college attendance became a draftavoidance behavior. This led to an increase in college attendance, and several studies have used induction risk as an instrumental variable for educational attainment (see e.g. Card and Lemieux 2001),<sup>5</sup> in some cases to estimate the effect of college education on later-life smoking (de Walque 2007, Grimard and Parent 2007) or mortality (Buckles et al. 2016). This literature suggests that draft risk is associated with increased education and improved health.

In certain years, deferments were also available for men who were married or had children. As a result, draft avoidance behaviors also included getting married and having children (Kutinova 2009, Hanson 2011). Kutinova (2009) finds evidence of increased first births occurring between 8 and 10 months following an executive order ending marital deferments for childless men because it created an incentive to have children to qualify for the deferment that

> 5 However, whether the increase in educational attainment during the Vietnam War is due to draft avoidance or use of the GI Bill is a matter of debate (Angrist and Chen 2011).

6
remained available for fathers. Hanson (2011) finds that young men married at younger ages during periods in which marital deferments existed. While a large literature supports the notion that married individuals are generally healthier than single individuals, this is not necessarily a causal relationship (Wood, Goesling, and Avellar 2007).

To address this mechanism, our models control for education, marital status, and number of children. We are not able to control for age at first marriage or age at first birth, so our controls for these variables may be imperfect. However, to the extent that education and marriage promote health, failure to perfectly control for them should bias our estimates toward finding that exposure to induction risk is associated with better health later in life.

# **3. Data**

The primary data used in this project are: 1) the National Health Interview Survey (NHIS) and 2) induction data taken from Reports of the Director of the Selective Service. In this section, we describe these data and document how we constructed the variables used in our analysis.

# **3.1.National Health Interview Survey (NHIS)**

The NHIS is a cross-sectional, nationally representative data set of the US noninstitutional population. Each year, the NHIS interviews approximately 100,000 individuals, asking questions about basic demographic and socioeconomic characteristics, military service, height and weight (from which we calculate body mass index or BMI),<sup>6</sup> and self-reported health. We use data from the 1982-1996 NHIS for our main analysis sample. Based on our sample of interest - men born from 1937 to 1956 - our main analysis sample is aged 25 to 59 during 1982-

> 6 Body mass index (BMI) is equal to weight in kilograms divided by height in meters squared.

7
1996. The sample size varies between 119,000 and 140,000 depending on the regression model specification, due to missing values for certain variables.

Because height and weight measures come from self-reports, they likely suffer from reporting error (Bound et al. 2001; Cawley et al., 2015). We adjust these measures for reporting error using data from the National Health and Nutrition Examination Survey (NHANES) III (1988-1994), which include both self-reports and measurements of weight and height and are from a similar time period as our NHIS data (Burkhauser and Cawley 2008).<sup>7</sup> From 1982-96, NHIS respondents were asked whether they had ever served in the US military and, if so, during which period (e.g. World War II, Korean War, Vietnam War). We do not use NHIS data from before 1982 because in those earlier years the NHIS data do not include month of birth, which we use to construct a more accurate measure of induction risk. We do not use NHIS data from after 1996 because in those later years the NHIS only asked whether respondents had been “honorably discharged” from the military, not whether they had served during the Vietnam War era (or served at all but without an honorable discharge). We focus only on the years in which we have the most complete military data (1982-96), however we extend our sample through 2012 as a sensitivity analysis.

Our sample is limited to individuals born in the calendar years 1937 to 1956. This is to avoid any contamination of our main analysis sample with individuals serving in the Korean War, which ended in July 1953. Thus, any individual born in 1937 would not have been eligible

> 7 Using the NHANES data for the same age range as our NHIS data (age 25-59), we estimate the following regressions separately by gender: ������������h�� = �� + ������������� + �������������� + �� + �� (1) Where SelfReport refers to self-reported weight, and X includes age and race (non-Hispanic Black, non-Hispanic other race, and Hispanic).  We then save the constant and coefficient estimates from these regressions and create an adjusted measure for weight in the NHIS sample by multiplying the NHIS self-reported weight values and demographic characteristics by their coefficients from NHANES regressions, and adding them together, along with the constant from the regression model. We perform a similar adjustment for self-reported height. Using these constructed values, we create an adjusted measure of BMI and obesity (BMI≥30) which we use throughout the rest of this manuscript. We also estimate all models using the non-adjusted BMI and obesity measures and find slightly larger and more statistically significant results using unadjusted variables.

8
to serve in Korea. de Walque (2007) also imposes this sample restriction.<sup>8</sup> Because we are interested in educational attainment, we limit our sample to those over age 25 at interview as most individuals have completed their schooling by this age. We further restrict our sample to those with valid measurements of height and weight because we use these to create BMI.<sup>9</sup> In certain analyses, we use a restricted-use version of the NHIS which provides us with data on state of birth (blinded),<sup>10</sup> whether and in which specific year an individual died if he or she died by 2011 (NHIS-Mortality Linked File), and his or her age of death. These mortality data were collected by matching NHIS participants annually to the National Death Index system death certificates by a combination of social security number, gender, first and last name, date of birth, or birth month and year.

# **3.2.Selective Service Reports**

We use annual (1955-1966) and semi-annual (1967-1975) reports of the Director of the Selective Service for induction eligibility, the number of monthly inductions, as well as additional institutional details and troop level data. These induction data are available by month, which we use to construct our measure of induction risk. We calculate risk based on the relevant laws governing both the pre-lottery years and the lottery years of the draft (see Appendix for more details on the history of the draft). We calculate induction risk as the number of inductions in a given 12 month period, using month and year of birth and monthly induction numbers from

> 8 We also perform analyses using 1930-1956 birth cohorts in sensitivity analyses reported in section 5.4. This sample would have been completely ineligible to serve in WWII, which is an important restriction as we only want to consider the post WWII induction system, created in 1948.

> 9 To be consistent across the years of NHIS, we drop individuals below 59 inches and above 76 inches, and those weighing less than 100 pounds and more than 285 pounds, the most restrictive data publishing policies used by NHIS over the years of our sample.

> 10 This measure allows us to determine individuals who were born in the same state, permitting us to estimate models including state fixed effects. However, this measure is only available for a subsample of our data.

9
annual reports to construct a measure of induction risk by month of birth, divided by the number of individuals at risk or: Where RAm,y is the risk at age 18 for those of age A born in month m in year y. We calculate the denominator, _Size of Cohort at Risk,_ using the induction reports for the official number of individuals who have registered for selective service and are between the ages of eligibility (e.g. 181⁄2 to 26) for the given period.<sup>11</sup> We calculate risk separately for ages 181⁄2, 19, ..., 26, which we then sum to calculate induction risk from 181⁄2 to 26. We focus on 181⁄2 to 26 rather than college years (e.g. 19-22), which was the focus of previous research (Card and Lemieux 2001, de Walque 2007, Grimard and Parent 2007, Buckles et al. 2016), because ages 181⁄2 - 26 were the actual, legislated ages at which an individual was at risk of induction.<sup>12</sup> We calculate the total risk as follows, taking into account that one remains at risk of induction only if one was not previously inducted:

> 11 We also perform this calculation using measures of the cohort of age 17 year olds as reported by the Department of Education (and creating measures of those between the ages of 181⁄2 - 26, by assuming the cohort of 17 year olds in a given year will be the correct number of 18 year olds in the following year). Our results are robust to these multiple methods, so we use the official number of individuals registered via the selective service throughout.

> 12 For years in which the draft lottery system was in place, we only consider eligibility for those in the birth cohorts at risk.

10
InductionRisk18 1 my = R18 my + (1—R18my)R1I9my + (1 — R18my )(1 — R19 my )R20m,y + (1-R18n,y)(1 — R19my)(1 — R20 my) * R21, + (1—R18n,)(1 — R19my)(1 — R20my)(1 — R21m,y) * R22my + (1-R18,5)(1 — R19py)(1 — R20m,y)(1 — R21n,y)(1 — R22m,y)(1 — R23 my)(1 — R24my)(1 — R25my) * R26m,y Hit = Bo + BylnductionRiskmyop + P2Xit + Sage + Ve + Fit Hit
denoting poor and 5 denoting excellent health).<sup>14</sup> We estimate probit models for the binary dependent variables obesity (BMI≥30), fair or poor health (self-reported health ≤ 2), and very good or excellent health (self-reported health ≥ 4) of the following form: ��(���) = ������������������,��� + ����� + ���� + �� + ���� (5) For each of these models, ��� are demographic and human capital characteristics described below, δ are fixed effects for age at interview, γ are fixed effects for year of interview, and ε is an error term. We report marginal effects from the probit models. We limit our main analysis sample to men who did _not_ serve in the military during the Vietnam War Era.<sup>15</sup> In all specifications, we cluster standard errors at the birth year cohort level.

We estimate three models, adding progressively more covariates in each specification. We start with the most exogenous set of regressors and then add regressors that control for ways in which induction risk could affect later-life health (e.g. education, marital status). We interpret any remaining association of induction risk with later-life health, after controlling for education and marital status, as the result of stress, although we acknowledge that we cannot measure stress directly.

The basic specification is limited to the most exogenous regressors: race (non-Hispanic Black, non-Hispanic other race, and Hispanic, with non-Hispanic Whites the omitted reference group), a birth cohort specific trend, defined as birth year minus 1937, and indicator variables for age and year. Specification 2 adds covariates for family size and marital status at the time of the NHIS interview. These additional covariates reflect the fact that the Vietnam War has been

> 14 We also estimate regressions with self-reported health as the dependent variable using an ordered probit and find qualitatively similar results; the results are available upon request.

> 15 We can calculate the aggregate probability of induction for men who did not serve in the military. We cannot do this for men who did serve - we do not know when they enlisted or whether they were drafted or in what year they were drafted. Moreover, the relevant measure of stress for them is likely not their risk of induction but their experiences during the war, about which we have no information.

12
linked to increased marriage and fertility rates (Kutinova 2009, Hanson 2011). While stress may affect later life health directly, in the form of induction risk, stress will also affect health through an increased likelihood of marriage and having children. Specification 3 additionally includes years of education past high school, and log income, which are endogenous variables but possible mechanisms through which induction risk may affect health (see e.g. Card and Lemieux 2001).

We also investigate the effect of stress in early adulthood on the risk of mortality, using a restricted-use version of the NHIS that contains data on mortality. Using a Cox proportional hazards model, we estimate time to death for men who never served during the Vietnam War. This equation takes the form: �(���) = ��(���) �<sup>����������������,���������������������</sup> (6) where �(���) is the hazard of dying by 2011, the year in which the NHIS-Mortality linked file follows individuals. Induction risk and other covariates are exactly the same as described above and we perform the same three specfications.

As a falsification test, we also estimate our models for male veterans. Men who served in the military during the Vietnam War at some point joined the military (we do not know whether they voluntarily enlisted or were drafted, or at what age they joined the military) and were then no longer at risk of being inducted. Moreover, those who served in the military during the Vietnam War faced many other stressors during these ages (e.g. combat, separation from loved ones, injury, deaths of fellow soldiers); we have no way of quantifying this stress but there is no reason to believe that it is correlated with induction risk for others of the same age who did not serve.

13
As an additional falsification test, we estimate models for women. Women were at zero risk of induction throughout this era, so as a falsification test we assign them the induction risk experienced by men of the same month and year of birth. This is a strong falsification test in that women of this age cohort may have experienced stress due to the risk that their brothers, boyfriends, or husbands might be inducted. However, the induction risks of those people would be based on their own birth month and year, not the birth month and year of the woman. Still, women may have experienced stress about their classmates, who are of similar age.

If we find a similar correlation between induction risk and later-life health for these placebo samples (veteran men, women) as we find for our main sample of men who did not serve in the military during the Vietnam War, that would suggest that the correlation is due to cohort effects or other trends at the time. In contrast, if we find a considerably different pattern between induction risk and later-life health for non-veteran men than for the placebo samples, that would be consistent with stress affecting later-life health. Falsification tests are never conclusive; one cannot prove the null hypothesis of no bias, but failure to reject the null is informative.

# **4.1.Sample Selection**

A potential concern with this study is that there will be sample selection on health status in who serves in the military based on the level of induction risk. This selection arises because of potential composition effects caused by variation in military force needs. As the need for more soldiers increases, the induction risk also increases, leading to more inductions and thus potentially culling more of the healthier individuals into service. In this case, during periods in time in which induction risk was particularly great, the health composition of men not inducted into the armed forces might be slightly lower, which would bias us towards finding a correlation of induction risk on health. We look for evidence of this in the results of the regression models 14
estimated for veterans; if induction takes place in order of healthiness, then when induction risk is higher, it should be associated not only with lower average health among the non-Vietnamveterans, but also lower average health among the veterans, who had less healthy individuals join their ranks.

Premature mortality due to stress is another potential source of selection bias. If those who were severely stressed by the possibility of being inducted into the military during the Vietnam War were more likely to die before our sample period, then our analyses would be biased away from finding that stress worsens later-life health. We explore this possibility by estimating models of mortality for the time period we can observe.

Finally, those with higher socioeconomic status may have been more adept at avoiding military service either through family connections or greater resources. If higher socioeconomic status individuals tend to have better later-life health (Grossman, 2015), and were more likely to avoid military service during periods of increased induction risk, then our estimates would be biased against finding a negative health effect of induction risk later in life. However, those of higher SES may have consistently used any advantages to avoid military service; i.e. that such avoidance did not vary with the overall induction risk.

# **5. Empirical Results**

We report summary statistics in Table 2. The average of military induction for all NHIS men is 7.7 percent. For some birth cohorts, namely 1946 and early 1947, induction risk surpassed 15 percent. Predictably, the men who ultimately served in the military during the Vietnam War were at higher induction risk than those who did not serve, 10.3 compared to 6.9 percent. Over 24 percent of the male NHIS sample served in the military during the Vietnam War. An additional 14 percent of men who did not serve in the military during the Vietnam War era 15
served in the military at some other point in time.<sup>16</sup> For women, true induction risk is zero throughout the war, but in Table 2 the induction risk listed for women is that for men of the same birth month and year; this is used as a falsification test later in the paper.

Table 2 also shows that the mean body mass index in the male sample is 26.5, with 19 percent classified as obese (BMI>=30). Over 70 percent of the male sample reported very good or excellent health with only 8.3 percent reporting fair or poor health.

Figure 1 displays total inductions by month over the Vietnam War era. Inductions over this time period are driven by manpower needs of the army. There was a brief increase in inductions caused by the Berlin Wall crisis (1961), then another large spike from 1966-1968 because of combat needs in the Vietnam War. Following the election of Richard Nixon, inductions dropped sharply as the US switched to a “Vietnamization” policy in which the US began withdrawing troops and turning over control of combat operations to South Vietnamese soldiers (Gartner 1998). Importantly, inductions fluctuate greatly over this time period and move in a non-linear pattern. Figure 2 shows induction risk by birth month and year cohort over our study period. This figure presents our actual measure of induction risk for each birth month and year as calculated using equation (3). The extreme variation and non-monotonicity in induction risk is very useful, as it implies that our regressor of interest is unlikely to be correlated with omitted variables such as general trends in health.

Table 1 shows the years and ages at which a birth cohort was at risk of induction and provides a clearer picture of the source of variation in risk due to the number of years a given birth cohort was at risk of military induction. It also separately identifies the type of induction

> 16 We remove those individuals who served in the military at any time in a subsequent sensitivity analysis, but these men are included in our main sample because they may have been stressed by the risk of being inducted during the Vietnam War.

16
system being used during the cohorts’ age-eligible years, with ages in italics denoting that the draft lottery system was in place from 1970-1972.

# **5.1.Results: Men Who Did Not Serve in Vietnam**

Table 3 presents results for men who did not serve during the Vietnam War, controlling for time trends, race and ethnicity, and age and year of survey fixed effects, while Table 4 also includes controls for family size and marital status at the time of interview. Results from these models are similar, so we discuss only the Table 4 results. Among male non-Vietnam-veterans, a 10 percentage point (2 standard deviation) increase in induction risk is associated with a 0.5 percentage point (3%) increase in obesity, a 0.7 percentage point (8%) increase in fair or poor health and a 0.5 percentage point (1%) decrease in the probability of being in very good or excellent health. All these results are statistically significant at least at the 10 percent level.

In Table 5 we also include controls for years of education completed beyond high school and log income. This is an important change to the model, because college education was a draft-avoidance behavior, and educational attainment is consistently associated with better laterlife health (see, e.g., Cutler and Lleras-Muney, 2010). The coefficient on induction risk becomes larger and more statistically significant in this model. A 10 percentage point (two standard deviation) increase in induction risk is associated with a 0.2 unit (1%) increase in BMI, a 1.5 percentage point (8%) increase in the probability of obesity, a 0.05 unit (1%) decrease in selfreported health, a 1 percentage point (10%) increase in the probability of being in fair or poor health and a 2 percentage point (3%) decrease in the probability of being in very good or excellent health. Income and education are both associated with better self-assessed health, and education is also associated with a lower probability of obesity (income is negatively correlated with obesity, but it is not statistically significant).

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# **5.2.Mortality**

Table 6 presents results from a Cox proportional hazard model of mortality following equation (6). Panel A reports results for men who did not serve in Vietnam, our main analysis sample. The results of specification 1 and specification 2 (which adds controls for marital status and family size) suggest a slight, statistically significant protective role of induction risk on the hazard of death. However, in specification 3, when we include educational attainment and income variables, this association becomes smaller and statistically insignificant.

The negative correlation between exposure to stress and later-life mortality is the opposite of what one would expect. In the next section, devoted to falsification tests, we will provide evidence that suggests that these mortality results, but not the results for weight and selfassessed health, are due to cohort effects.

# **5.3.Falsification Tests: Male Vietnam War Veterans and Women**

In Table 7 we present results for the same models that were estimated using samples of: male Vietnam veterans (results shown in Panel A) and women (Panel B). In the interests of being concise, only the coefficients on induction risk are shown in the table, but full results of the models are available upon request. The results from these models are substantively different from those for male non-Vietnam-veterans in Tables 3-5. In Panel A for male Vietnam veterans, the coefficient on induction risk for BMI and the marginal effect of induction risk for obesity are very small and not statistically significant. In addition, induction risk is consistently associated with _better_ self-assessed health among veterans, which is the opposite of the pattern observed for non-veterans. For example, in specification 2 for veterans, a one percentage point increase in induction risk is associated with a 0.005 unit (0.1%) increase in self-reported health, a 0.14 18
percentage point (1.8%) decrease in fair or poor health and a 0.24 percentage point (0.3%) increase in very good or excellent health. Adjusting for family income and educational attainment in specification 3, the estimates on fair or poor health and very good or excellent health remain statistically significant although they are only about half as large as in specification 2, while the estimate for self-assessed health overall is both smaller and no longer statistically significant.

Results for women in Panel B of Table 7 are somewhat similar to those for Vietnam veterans from panel A, but very different from those of male non-Vietnam-veterans that were shown in Tables 3-5. Induction risk is uncorrelated with BMI and obesity. It is correlated with self-assessed health, but positively, which is the opposite of the pattern found for the male nonveterans in our main sample, but the same pattern as found for the other placebo sample of veteran men. Specifically, the results from specification 2 for women indicate that a one percentage point increase in induction risk is associated with a 0.0025 unit (0.1%) increase in self-assessed health, a 0.07 percentage point (0.6%) decrease in the probability of being in fair or poor health, and a 0.09 percentage point (0.1%) increase in the probability of being in very good health. In the third specification that controls for education, the only statistically significant correlation is that a one percentage point increase in induction risk is associated with a 0.03 percentage point (0.3%) decrease in the probability of being in fair or poor health.

The results of the falsification tests indicate that the correlation between induction risk of men born in a given month and year does not have the same correlation with later-life mortality for the placebo samples of veteran men and all women as we found for our sample of interest who are non-veteran men. In fact, the correlation for the placebo samples was generally of opposite sign; whereas we found that non-veteran men exposed to greater induction risk are in 19
worse later-life health, the opposite was true for the placebo samples. The results of these falsification tests yield no evidence that the results for the sample of interest are due to cohort effects or unobserved trends.

The results of the falsification test do, however, raise the question of why there is a positive correlation for the placebo samples. It is possible that there are birth cohort effects that are visible in the placebo samples and that cause attenuation bias in our sample of interest. For example, previous research (e.g. Robinson et al. 2012) has documented evidence of birth cohort effects on abdominal obesity, especially among women, which may partially explain the positive association between health and induction risk for women, although we find very little consistent evidence of an association between BMI or obesity and induction risk for women or male veterans in Table 7. Overall, the results of these falsification tests suggest that the negative association observed for male non-Vietnam-veterans between induction risk and worse later-life health is not due to a cohort effect or trend in unobserved variables. Although falsification tests cannot be definitive, these are consistent with stress having an adverse impact on later-life health.

The falsification tests for mortality yield a different result. Results of hazard models of mortality are listed in Table 6, Panel B for veterans, and Table 6, Panel C for women. For both placebo samples, induction risk has a similar correlation with later-life mortality as it has for our main analysis sample of male non-veterans. For all three groups, higher induction risk is associated with a lower probability of mortality. In fact, the point estimates are larger for the two placebo samples than for the main analysis sample of male non-veterans. Based on the results of these falsification tests, we conclude that the correlation is not an effect of exposure to stress but is instead a cohort effect.

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# **5.4.Additional Sensitivity Analyses**

# **_State Fixed Effects_**

In Appendix Table A1, we present results from a specification similar to Tables 3 – 5, but with the addition of controls for state fixed effects. Results are qualitatively and quantitatively similar. We focus on the specifications without fixed effects for the following reasons. First, the restricted data with state markers are not available for our full 1982-1996 analysis sample: NHIS only began collecting these data in 1985 and the information is missing for a portion of individuals in later years as well. We lose approximately one-third of our sample in state fixed effects models. Second, this variable refers to state of birth, not state of residence at the time of induction risk, and is thus an imperfect control for time invariant observable and unobservable differences in one’s state at the time of induction risk.

# **_Compositional Changes_**

To investigate whether our results reflect compositional changes among non-Vietnamveterans, we estimate a model for all men (non-Vietnam-veterans and veterans) pooled. The logic is that there could be compositional change in our sample: when induction risk is higher more healthy men leave the pool of non-veterans and mechanically make the pool of nonveterans less healthy, both during the War and later in life. If such a change were occurring and less healthy men were being left behind when induction risk rose explained our earlier results, then pooling non-Vietnam-veterans and veterans should show no association between induction risk and later-life health. In Appendix Table A2, we reprint our main induction risk results in Panel A and we present the new results for all men pooled in Panel B. We include an indicator variable for veteran status in these estimates. The results of specification 3, which control for education, are robust to pooling all men, although they are also smaller in magnitude (as one 21
would expect from adding men to the sample whose stress is not well captured by the average induction risk). Overall, we continue to find evidence that stress, in the form of induction risk, worsens later-life health.

# **_Variations in Sample Inclusion Criteria_**

We also examine the sensitivity of results to variation in the sample inclusion criteria. These results are presented in Appendix Table A3, with Panel A reprinting our main results on induction risk from Tables 4 and 5 for easy comparison.<sup>17</sup> In Panel B, we present results when those who ever served in the military, not just during the Vietnam War era, are dropped from the sample. In Panel C, we include only non-Vietnam-veteran men who responded without a proxy to the NHIS survey. The purpose for doing this is to eliminate any additional reporting error due to health being proxy-reported instead of self-reported. In Panel D, we include in the sample all birth cohorts of male non-Vietnam-veterans back to 1930, who would have been of military age starting in 1948 and thus subject to the same post World War II draft system as those in our main sample. In Panel E, we limit the sample to those born between 1930 and 1936 who did not serve in the military, but were age-eligible to serve during the Korean War. These results are generally similar to those of the main specification; exposure to a higher induction risk tends to be associated with a higher probability of obesity and worse self-assessed health.

# **_Model Estimates for Veterans of Various Wars_**

We estimate additional falsification tests, using data for male veterans of wars other than Vietnam in Appendix Table A4. The results generally confirm that veterans, no matter which war they served in, do not exhibit the negative correlation between induction risk (that was found

> 17 We do not present estimates on induction risk for specification 1 because these estimates are very similar to those from specification 2.

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for men who did not serve) and later-life health; the exception is that Korean veterans exhibit a positive correlation between induction risk and later-life BMI and obesity.

# **_Alternate Measure of Stress: Risk of Being Killed in Action_**

We also estimate models using an alternate measure of stress. Specifically, the new proxy for stress is the interaction of induction risk with the probability of being killed in action, calculated as the number of deaths in a calendar year divided by the level of American troops in Vietnam in that year (de Walque 2007). The logic is that stress is raised not simply by the probability of serving in the military but also by the chances that one could be killed. We create this interaction in a similar fashion to equation 3. We present results of these estimations in Appendix Table A5, Panel A. These results are qualitatively similar to those in the main specification: greater stress (proxied by higher risk) is associated with a higher probability of obesity and worse self-assessed health.

# **_Alternate Measures of Expected Induction Risk_**

We also explore other plausible proxies for stress. It may be that individuals are not able to perfectly forecast their risk of induction; instead, they may observe the rates of induction for the cohorts ahead of them and assume that they will face similar risks. To explore this possibility, we estimate our base model, but assigning individuals the induction risk of cohorts that came of military age 1, 2, or 3 years before them. In Appendix Table A6, the results suggest that the risk of military induction of one’s own cohort has the largest effect on later life health. The size of the effect on health using risk of induction for older cohorts tends to decrease with the distance of the cohort, suggesting previous induction risk affects later cohorts but that they update their own risk calculations as they get closer to induction age.

# **6. Discussion**

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We find evidence consistent with the hypothesis that stress in adolescence and early adulthood worsens later-life health. Specifically, a greater risk of military induction during the Vietnam War is associated with worse later-life health for men who did not serve in the military. These adverse health effects are modest, but are relatively robust, and include a higher risk of obesity and higher probability of reporting being in worse health. Falsification tests conducted with samples of women and male veterans do not show the same pattern for obesity and selfassessed health, which suggests that those results are not due to cohort effects or trends in unobservables. Moreover, it does not appear to be due to compositional effects (i.e., more healthy men being removed from the ranks of non-veterans when induction risk is high), because the negative correlation is still detectable (though, naturally, weaker) in a sample in which the non-veterans are pooled with veterans. The finding that stress is associated with a greater risk of obesity and worse self-assessed health in later life is robust to alternate proxies for stress (such as the probability of being killed in action) and various sample inclusion criteria.

For the outcome of mortality, however, the falsification samples exhibit the same patterns as the main analysis sample, which leads us to conclude that the correlation between induction risk and later-life mortality is due to cohort effects or other omitted variables.

This study has a number of limitations. First, we cannot directly measure stress. No largescale survey that we know of has measured the stress of individuals using cortisol laboratory measurements at the time of the Vietnam War. However, the measure we use, which we limit to those who did not serve in Vietnam, captures an important source of uncertainty faced by individuals at that time. For those who do not serve, we do not have baseline health measures to investigate whether they did not serve due to preexisting health conditions that would bias these individuals towards worse health later in life. However, this should not bias our results unless 24
health varies by month and year of birth in a way that is correlated with induction risk, which seems unlikely.

Among veterans, we cannot distinguish those who volunteered immediately for service from those who were inducted after experiencing the stress of the draft. However, this should bias the coefficient on risk in the veterans model towards showing ill effects of draft risk on later-life health, which we do not find for the veteran sample. Finally, we are limited in the laterlife health outcomes that we can examine by the questions that were asked in NHIS.

Overall, we find a consistent association between a proxy for stress and worse later-life health. One possible mechanism by which stress affects later life health is diet. Reviews have concluded that chronic stress is associated with eating energy-dense foods (i.e., foods higher in sugar and fat) and weight gain, with greater effects for men (Torres and Nowson, 2007). Another possible mechanism is the stress hormone cortisol; it is believed that long-term hyperactivation of the system that regulates cortisol can contribute to the development of obesity and metabolic syndrome, which includes hypertension, diabetes, and high cholesterol (Jackson et al., 2017). These findings are consistent with our estimates linking stress in young adulthood to obesity and worse self-reported health later in life.

This study contributes to the literature on the adverse later-life consequences of stress, most of which has focused on the effect of stress or insults at the earliest ages (Almond and Currie, 2011; Aizer et al., 2016; Camacho, 2008). Specifically, this study establishes that even stress in adolescence and early adulthood may be associated with worse later-life health.

This paper also contributes to the previous literature on the effects of education on laterlife health. Specifically, while some previous studies used induction risk as an instrument for education, the results of this paper suggest that in some contexts it may be an invalid instrument, 25
as induction risk may affect outcomes such as health directly, not only through the mechanism of education.

The policy implications of this study are that even systems that seek to allocate burdens in a fair and transparent way (e.g., draft lottery) may impose unanticipated costs on participants through the mechanism of stress. In our study, we show that this is true even of those who never serve in the military.

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# **Appendix A. The Vietnam Conflict and the Risk of Induction into the U.S. Military**

Following the French military departure from Vietnam in 1954, the US began to directly aid the South Vietnamese government, and US military advisors began training the South Vietnamese military in 1955 (“Chronology of Events Relative to Vietnam, 1954-1965,” 1965). This growing influence in Vietnam did not affect US military inductions until the Gulf of Tonkin Incident in 1964 in which a US ship engaged the North Vietnamese navy in the Gulf of Tonkin (“Chronology of Events Relative to Vietnam, 1954-1965,”1965). Following this incident, induction rose rapidly, peaking in October 1966, and again in the first half of 1968 before decreasing rapidly; see Figure 1. Prior to U.S. involvement in Vietnam, induction levels also were high in the second half of 1961 due to the building of the Berlin Wall, and in the early 1950s due to the Korean conflict.

The risk of fighting in the Vietnam War took on a particular salience unseen before due to its novelty as America’s first “televised war” (Hallin 1986, pp. 105). Before the first official exchange of fire in 1964, US publications printed disturbing images of a Buddhist monk’s selfimmolation in protest of the US backed Diem government (Hallin 1986). Then in August 1965, CBS aired footage of US Marines burning Cam Ne, a village of seemingly little strategic value and few, if any, enemy combatants (Engelhardt 2007). The particular brutality of that broadcast shocked Americans and suggested US troops were performing atrocities in Vietnam. While coverage of the war continued to skew towards pro-US government coverage in the mid-1960s, news outlets continued to show explicit war clips depicting death and destruction (Engelhardt 2007, Hallin 1984).

As the U.S. death toll rose in Vietnam, political unrest in the US grew with student protests and draft card burnings (Appy 2003, Engelhardt 2007). The fear among Americans of 27
being inducted into the military during this time period was felt at all levels, including among presidential candidates. During his 1968 Presidential campaign, Nixon campaigned on a platform that included abolishing the draft and implementing an All-Volunteer Force (Rostker 2006).

In 1969, President Nixon initiated a “Vietnamization” policy which greatly curtailed the need for new inductees into the military. This policy required South Vietnamese troops to assume control of combat missions while the US drastically reduced troop levels in Vietnam (Gartner 1998). Nixon was able to create an all-volunteer force when Congress allowed the legislative mandate to induct citizens into the military to expire in 1973. Later in 1973 Congress passed the Case-Church amendment that officially ended direct US involvement in Vietnam.

A.1. Induction Process Individuals at this time could enter military service in three ways by: (1) voluntary enlistment; (2) voluntary induction; (3) involuntary induction. Those who enlisted voluntarily served a longer tour of duty, but had a choice in their branch of service and military occupation (House Armed Services Committee, 1970 via Angrist, 1991). Voluntary inductees, on the other hand, served a shorter tour of duty with no choice of military occupation and while they were certain to serve, they controlled the timing of their service (Annual Report, 1955, Semi-Annual Report, 1968, Angrist, 1991).<sup>18</sup> Involuntary inductees were similar to voluntary inductees in terms of length of tour and no choice in military occupation, but were not certain they would serve in the military and had no control over the timing of their service.

Voluntary enlistments alone were not enough to maintain an adequate fighting force during this era (Annual Report of the Director of the Selective Service System, 1955). Draft-

> 18 These volunteers for induction were generally younger than regular inductees and may have been trying to join the military so that their service did not interrupt their lives at a later age; they received no preferential treatment besides expedited delivery into the Armed Forces (Annual Report, 1955, Semi-Annual Report 1968).

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eligible males would sometimes volunteer in order to choose their branch of service; as a result, enlistments and inductions were correlated - when inductions dropped, enlistments also dropped, necessitating inductions to meet military manpower needs.

The process of inductions proceeded as follows: The Director of the Selective Service System received a monthly call for inductions from the President and Secretary of Defense (Annual Report, 1955). The director then delivered these calls for induction to State-level directors of Selective Service, who sent these requisitions to the local boards in the state. To ensure an equitable system by state, requisitions were sent out proportionately depending on the number of eligible registrants by state, and states further received credit for the number of residents currently serving in the military (Annual Report, 1955).

Local boards conducted pre-induction examinations in order to have induction-eligible individuals ready when they received calls from the State Director. Approximately half of all examinees were cleared for service (Annual Report, 1966). An additional 20 percent were rejected for service after being delivered for induction (Annual Report, 1966; Angrist, 1991). Those passing pre-induction medical exams were sent to Armed Forces induction stations.

A priority system dictated the order of induction; generally, delinquents (a classification of involuntary inductee) received the highest draft priority, followed by volunteers for induction.<sup>19</sup> The priority of involuntary induction after the two classes above varied during the Vietnam War period, with various marital, paternal, and student deferments created, modified, and repealed. The lexis chart in Table 1 summarizes which ages of young adults were eligible for induction by year, and Appendix Figures 1 and 2 give a brief summary of changes in the

> 19 Delinquency is defined as failure to comply with the Universal Military Training and Service Act. Examples are refusal to register, failure to supply board with information, failure to report for pre-induction examination, or failure to report for induction (Annual Report 1952). Any person of ages 18-26, under provision part 1630 of SS regulations, can offer themselves for induction at any point in time. Persons between age 17 and 18, with the approval of a guardian, also can volunteer for induction (Annual Report 1955).

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induction system from 1948 through the end of the induction system and the beginning of an allvolunteer force in 1973. Our data do not allow us to determine an individual’s eligibility for specific deferments, so they are not used in our calculation of induction risk.

Executive order 10659 provided a new order for inductions, one created to prevent older registrants (those 26 or older) and fathers from being high priority inductees (Annual Report 1955, pg. 27). Under this order, the next highest priority groups after delinquents and volunteers became those aged 19-25, without children, chosen by age, oldest first,<sup>20</sup> followed by those of similar ages with children. Then those aged 26 or older were chosen by age, with the youngest receiving calls for induction first. Some deferments, including student deferments, extended the age at which one could be inducted to age 35 (Annual Report 1953).<sup>21</sup> Finally, if local boards could not fill their quotas using the previous groups, those aged 181⁄2, but not yet 19, could be called, oldest first.

The US selective service enacted the first draft _lottery_ on December 1, 1969 (Selective Service System, 2012). Birth dates were randomly selected to determine draft priority for those born between January 1, 1944 and December 31, 1950.<sup>22</sup> Individuals were at risk of induction for the calendar year 1970, when they were aged 20 to 26, after which point they could not be called for induction. Subsequent draft lotteries included single birth cohorts; e.g. the 1970 draft, in which individuals were at risk of induction during the 1971 calendar year, applied only to the 1951 birth cohort, such that all inductees in these drafts were age 20. The final draft lottery from which inductees were called for service occurred on August 5, 1971 and affected the 1952 birth

> 20 Previous research using induction risk as an instrumental variable for education looked only at risk during certain college ages (e.g. de Walque, 2007, used ages 19-22), but actual risk extended well past that. The priority of drafting the oldest first underscores the importance of including post-college years in induction risk.

> 21 Few, if any, individuals over the age of 26 were called for induction.

> 22 The 1969 draft lottery was skewed towards higher priority calls for those with December birthdays apparently due to inadequately mixed draft balls (Fienberg 1971 via Lindo and Stoecker 2014). This issue was corrected in later draft lotteries.

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cohort. However, the Selective Service continued to conduct the draft lottery annually until 1975, with the understanding that should Congress reinstate the draft, inductions would be based on these draft lotteries. The last inductee was called in December 1972 and reported for duty in July 1973 (Selective Service System, 2012). Soon after in August 1973, Congress passed the CaseChurch amendment, ending direct US involvement in the Vietnam War.

The variation in probability of induction for our analysis sample is due to: 1) changes in the number of inductions by year that were driven by political decisions about the Vietnam War; and 2) changes over time in the ages that were eligible to be inducted or were subject to the draft lottery.<sup>23</sup>

> 23 Additional variation in induction risk existed at the state level. Buckles et al. (2016) exploits the across-state variation to estimate the effect of college completion on mortality. They find rather sizable effects of education on mortality using both national and state level induction risk to instrument for both educational attainment and veteran status, noting this effect likely operates through decreased smoking, improved financial security, and better health resources.  It seems unlikely that state-level variation in induction risk was well known at the time (Buckles et al. 2016). Thus, the national risk of induction may be a better measure of stress and perceived incentives for draft avoidance behavior.

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