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Psychological Science
http://pss.sagepub.com/content/early/2012/01/24/0956797611423545
The online version of this article can be found at:
DOI: 10.1177/0956797611423545
published online 24 January 2012Psychological Science
Joshua J. Jackson, Felix Thoemmes, Kathrin Jonkmann, Oliver Lüdtke and Ulrich Trautwein
Make the Military?
Military Training and Personality Trait Development : Does the Military Make the Man, or Does the Man
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DOI: 10.1177/0956797611423545
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Military experience is often viewed as a major turning point in
people’s lives that induces long-lasting changes (Elder, 1986;
Elder, Gimbel, & Ivie, 1991). Indeed, a long-held sentiment
exists that military experience socializes and matures individ-
uals (James, 1910/1988). For example, the recruiting materials
of military forces around the world bolster the idea of military
experience as being a catalyst for change. For example, recent
slogans in the United States, such as “Be all you can be,”
“Accelerate your life,” and “Aim high,” all imply that military
experiences affect life trajectories. Despite the expectation
that military experience influences character development, no
studies have examined this effect directly. Accordingly, in the
study reported here, we investigated the relation between mili-
tary training and personality traits in a longitudinal study of
German youth.
Although no study has examined the effect of military
experience on personality traits, there is evidence that military
experience affects the life course (Settersten, 2006). For exam-
ple, divorce is less common among military veterans than
among civilians, and military experience is also associated
with less earning potential than among individuals who have
never served (MacLean & Elder, 2007). Moreover, there
appears to be a relation between military experience and good
health (Wilmoth, London, & Parker, 2010). These life-course
outcomes are also predicted by personality traits (Ozer &
Benet-Martinez, 2006). As such, it is possible that changes in
personality traits mediate the relation between military experi-
ence and important life outcomes.
Few researchers go beyond examining life-course out-
comes (e.g., divorce) to test whether changes in psychological
constructs are associated with military experience. For exam-
ple, there is some evidence that military experience affects
political attitudes and values, though the effect is relatively
small after controlling for attitudes prior to entering military
service (French & Ernest, 1955; Jennings & Markus, 1977).
Changes in the emotional health of military veterans can
also occur, such as in the case of posttraumatic stress disorder
(Aldwin, Levenson, & Spiro, 1994), though these changes
typically arise from acute combat experiences and not from
military experience in general. Given the millions of individu-
als around the world who participate in some form of military
Corresponding Author:
Joshua J. Jackson, Department of Psychology, Washington University in
St. Louis, Campus Box 1125, St. Louis, MO 63130
E-mail: j.jackson@wustl.edu
Military Training and Personality Trait
Development: Does the Military Make the
Man, or Does the Man Make the Military?
Joshua J. Jackson1, Felix Thoemmes2, Kathrin Jonkmann2,
Oliver Lüdtke2, and Ulrich Trautwein2
1Washington University in St. Louis and 2University of Tübingen
Abstract
Military experience is an important turning point in a person’s life and, consequently, is associated with important life
outcomes. Using a large longitudinal sample of German males, we examined whether personality traits played a role during
this period. Results indicated that personality traits prospectively predicted the decision to enter the military. People lower
in agreeableness, neuroticism, and openness to experience during high school were more likely to enter the military after
graduation. In addition, military training was associated with changes in personality. Compared with a control group, military
recruits had lower levels of agreeableness after training. These levels persisted 5 years after training, even after participants
entered college or the labor market. This study is one of the first to identify life experiences associated with changes in
personality traits. Moreover, our results suggest that military experiences may have a long-lasting influence on individual-level
characteristics.
Keywords
personality, military, personality development, propensity score, agreeableness, adolescent development, life experiences,
causal analysis, environmental effects
Received 3/1/11; Revision accepted 8/19/11
Research Article
Psychological Science OnlineFirst, published on January 24, 2012 as doi:10.1177/0956797611423545
at WASHINGTON UNIV LIBRARY on January 25, 2012pss.sagepub.comDownloaded from
2 Jackson et al.
training (Hackett, 2008), we were interested in examining how
military training affects psychological constructs, such as per-
sonality traits.
A major obstacle in our study was the possibility that peo-
ple who choose military service and people who do not could
differ on important preexisting variables. These differences,
which reflect selection processes, could explain why military
service is associated with important life outcomes. For most
North Atlantic Treaty Organization countries, selection pro-
cesses play a major role in deciding who serves in the military.
For example, in the United States, individuals who have a
lower socio-economic status and IQ, come from rural versus
urban areas, are minorities, and associate with deviant peers
are more likely to join the military than individuals who
remain civilians (Elder, Wang, Spence, Adkins, & Brown,
2010; Johnson & Kaplan, 1991). Although values and atti-
tudes appear to differ among people who intend to join
the military and people who do not (Bachman, Sigelman, &
Diamond, 1987), little is known about what personality char-
acteristics are associated with enlistment. Personality traits
predict leadership ability, dropout, satisfaction, and mental
health during military service (Fiedler, Oltmanns, & Tur-
kheimer, 2004; McCormack & Mellor, 2002), but to our
knowledge, no study has prospectively examined personality
traits among individuals who eventually choose to serve in the
military and those who do not.
For those individuals who decide to join the military, mili-
tary training is explicitly set up to change their patterns of
behavior (Arkin & Dobrofsky, 1978). As such, military train-
ing combines a number of socialization processes that provide
an ideal environment in which personality trait changes can
occur (Roberts, Wood, & Caspi, 2008). First, expectations for
specific behaviors and norms are made explicit. New recruits
are immersed in an extensive boot-camp program, in which
their civilian status is broken down and the new identity of
military recruit is forged. Second, an incentive structure is set
up that rewards recruits who fulfill the expectations of military
culture and punishes those who do not. These external contin-
gencies lead to changes in daily behavior that, over time, are
thought to promote changes in personality traits (Roberts
et al., 2008).
In the study reported here, we tested both selection and
socialization processes that lead to different life-course out-
comes using a longitudinal sample of young adult German
males. First, we tested whether personality traits assessed in
high school predict who eventually chooses to join the mili-
tary. Second, we tested whether individuals who received mil-
itary training were more likely to show changes in personality
traits than individuals in a control group were. If changes asso-
ciated with military experiences were found, we were addi-
tionally interested in whether these changes persisted after
military recruits went to college or entered the labor market.
Given that retrospective reports suggest that people view the
military as a time when they became more mature (Dar &
Kimhi, 2001; Elder, 1986), we hypothesized that military
recruits would experience changes in the personality traits
associated with maturity: Specifically, they would show higher
levels of conscientiousness and agreeableness, and lower lev-
els of neuroticism (Roberts et al., 2008). However, changes in
these traits already occur in young adulthood independent of
military training (Lüdtke, Trautwein, & Husemann, 2009;
Robins, Fraley, Roberts, & Trzesniewski, 2001), though it
should be noted that not all studies have found increases in
agreeableness. Given these changes, reports of increases in
maturity due to military training may be misattributed to nor-
mative developmental trends.
Another difficulty in estimating the effect of military train-
ing on personality traits is that participation in the military is
not randomized. If selection processes exist, they may bias the
interpretation that military experience leads to changes in per-
sonality. As a result, it becomes necessary to control for any
confounding preexisting differences, which we did using a
regression-based covariate model and propensity-score match-
ing. Propensity-score methods are slowly being incorporated
in psychological research (Thoemmes & Kim, 2011), but thus
far, they have not been used to investigate changes in person-
ality traits.
Method
Participants
Participant data came from a large, ongoing German study
(Transformation of the Secondary School System and Aca-
demic Careers, or TOSCA) initiated by the Max Planck Insti-
tute for Human Development and now conducted at the
University of Tübingen. The data were collected from two dif-
ferent cohorts of students at randomly selected upper second-
ary schools; there were 149 schools in the first cohort and 157
in the second cohort. The initial assessments of each cohort
were conducted 4 years apart. The schools are representative
of the traditional and vocational secondary schools (Gymnasi-
ums) attended by college-bound students. Schools and stu-
dents were randomly selected to ensure that the data were
representative of the population at large. Among the first and
second cohorts, 99% and 97% of the schools, respectively,
participated in the study. More than 80% of the students in
each school participated. Participants were first assessed in
their final year of high school prior to conscription (Time 1;
average age = 19.5 years) and then reassessed on average 2
years later (Time 2). In the first cohort, participants were
assessed at two additional time points, each occurring roughly
2 years after the previous assessment (Times 3 and 4, respec-
tively; see Trautwein, Neumann, Nagy, Lüdtke, & Maaz,
2010, for more information regarding the sample).
Germany is an ideal setting in which to examine the effect
of military training because of the laws that governed the con-
scription of male citizens at the time of data collection. By
default, all physically able male citizens of Germany are
drafted into military service. However, German males may
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Military Training and Personality Development 3
refuse military service (i.e., conscientiously object) by choos-
ing to perform civilian community service (e.g., work in a hos-
pital) instead. Accordingly, young adults who participated in
civilian community service served as a control group. At the
time of the first two TOSCA assessments, the conscription law
stated that all males were obligated to serve 9 months in the
military or participate in 9 months of civilian community ser-
vice, though some exemptions were granted (e.g., medical rea-
sons, having a brother in the military). Military service time
consisted of 3 months of combat training and 6 months at an
assigned post. Individuals who chose civilian community ser-
vice were required to work at institutions that provide public
services, such as hospitals and childcare centers. Military ser-
vice members are assigned to dormitories in barracks, whereas
participants who choose civilian community service often live
close to home or stay at home with their family.
Using data from both TOSCA cohorts, we extracted all
male participants who performed either military service or
civilian community service between the first assessment and
the second assessment. A number of TOSCA participants (N =
715) performed neither military nor civilian community ser-
vice and were thus not included in the primary analyses. The
final analytic sample included a total of 1,261 male partici-
pants, of which 245 performed military service and 1,016 per-
formed civilian community service.
Measures
We measured the Big Five personality dimensions at Times 1
through 4 using the German version of the NEO Five-Factor
Inventory (Borkenau & Ostendorf, 1993). Coefficient alpha
reliabilities were above .70 for all Big Five traits at all time
points.
Analyses
Some of the outcome variables and covariates had missing
data because of nonresponses or attrition. To fill in missing
data, we employed a multiple imputation scheme. We gener-
ated a total of 10 imputations using a fully conditional model
with a total of 67 social environmental and psychological vari-
ables (Table S1 in the Supplemental Material available online
lists these variables).
A major obstacle to investigating the effects of military
training on personality is that military training is not random-
ized; thus, preexisting differences between military recruits
and people who chose civilian community service may be
responsible for observed differences at later points in time. We
addressed this problem using several analytic approaches.
First, a standard regression-based covariate model was used to
control for levels of the Big Five personality traits before
entrance into the military. Second, propensity-score matching
was used to control for a large number of potentially con-
founding covariates. In this approach, each participant receives
an estimated propensity score, which is the conditional
probability that a given participant would be exposed to the
treatment condition (i.e., military training) given certain val-
ues on observed covariates. By matching participants that
have or have not been exposed to the treatment on this esti-
mated propensity score, we created pairs of participants that
were balanced on all observed covariates (a situation that
would be expected in a randomized experiment). This match-
ing process created two balanced distributions (with regard to
observed covariates) that differed only in terms of the treat-
ment they received (military training or civilian community
service).
In the first step of the model, we estimated propensity
scores for each individual by regressing the Time 1 social
environmental and psychological covariates on the binary out-
come variable (i.e., military service or civilian community ser-
vice). Next, we fitted this propensity-score model within each
of the 10 imputations (Hill, 2004). Within each imputation, we
conditioned the data on the estimated propensity score by
using a nearest-neighbor matching scheme, in which we
matched each person who participated in military service with
up to 2 persons who participated in civilian community ser-
vice. To ensure close matches, we employed a caliper width
of .2 standard deviations of the logit of the estimated propen-
sity score using the MatchIt package in R (Ho, Imai, King, &
Stuart, 2007). The matched samples were screened for balance
across main effects, interactions, and quadratic terms. The
matching algorithm produced adequate balance in each of the
10 imputations (see Table S2 in the Supplemental Material).
We estimated a treatment effect within each of the imputed
and matched samples, and we averaged this effect and the
associated standard errors (von Hippel, 2007). Across the 10
imputations, the average total number of participants was 867,
with an average of 241 participants who performed military
training and an average 628 who performed civilian commu-
nity service.
Additionally, to assess whether differences in personality
persisted once participants entered college and the labor mar-
ket, we examined the longitudinal trajectories of personality
traits using latent growth models. The first cohort included
two additional waves of data compared with the second
cohort—for a total of four waves of personality measures
across a 6-year time span. The matched sample for this
extended longitudinal data set included 106 participants who
performed military service and 433 who performed civilian
community service. We used service type as an explanatory
variable of latent growth to see whether the trajectories of per-
sonality in young adulthood differed between the two groups.
In a second-order latent growth model, the repeated person-
ality measures were modeled as latent variables as opposed to
manifest variables. To test long-term personality differences
between groups, we scaled the intercept parameter to represent
personality traits at Time 4. Fixing all loadings to unity identi-
fied the intercept parameter, and the slope parameter was set to
−3 at Time 1, −2 at Time 2, −1 at Time 3, and 0 at Time 4. Item
parcels were used to identify the repeated measures of the
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4 Jackson et al.
latent personality traits. Furthermore, the model was con-
strained for strict measurement equivalence across all time
points. Item loadings and residual variances were constrained
to be equal across the four waves of data, and the residual vari-
ances for each item were allowed to correlate across all time
points.
Results
Who chooses military service?
To examine selection effects in the matched samples, we tested
personality trait differences between the military-service
group and the civilian-community-service group at Time 1,
before the participants started service (see Table 1 for results).
Adolescents who eventually opted for military service were
initially less agreeable (d = −0.29, p < .05), less open (d =
−0.15, p < .05), and less neurotic (d = −0.14, p < .05) than
adolescents who selected civilian community service. These
results suggest that personality traits played a moderate but
significant role in the decision to select military training
instead of civilian community service.
Is military training associated with changes in
personality traits?
Before assessing whether military training is associated with
changes in personality, it is necessary to take into account the
existing pattern of personality trait development that occurs
during young adulthood. Specifically, people tend to increase
in conscientiousness, decrease in neuroticism, and sometimes
increase in agreeableness (Caspi, Roberts, & Shiner, 2005).
Results were consistent with these normative changes, in that
both people who chose civilian community service and mili-
tary recruits showed increased levels of conscientiousness (d =
0.33, d = 0.39, respectively, ps < .05) and agreeableness (d =
0.32, d = 0.21, respectively, ps < .05), and decreased levels of
neuroticism (d = −0.36, d = −0.39, respectively, ps < .05; see
Table 2 for mean levels of the Big Five personality traits for
the two groups).
To test whether military training was associated with
changes in personality traits, we next ran a series of models.
First, we examined the differences in personality traits between
groups at Time 2 after controlling for personality during high
school (Time 1). The results of these socialization analyses are
presented in Table 1. Military training was associated with
lower levels of agreeableness than civilian community service
was (d = −0.19, p < .001). No other personality traits were
significantly different between the two groups after control-
ling for personality traits in high school. Adding males who
did not participate in any form of service to the control group
did not significantly change the results. Furthermore, when
using these nonservers rather than people who chose civilian
community service as a control group, the effect of military
service on agreeableness remained similar in magnitude (d =
−0.13, p < .05). In contrast, examining the effect of civilian
community service on agreeableness by using the nonservers
as a control group yielded no significant findings (d = 0.06,
Table 1. Results of Three Models Testing Personality Trait Differences Between the Military-Service
Group and the Civilian-Community-Service Group
Personality trait and statistic Selection model Socialization model Propensity-score model
Extraversion
Raw difference 0.01 (0.03) 0.00 (0.03) −0.01 (0.04)
Cohen’s d0.03 0.00 −0.02
Agreeableness
Raw difference −0.10 (0.04) −0.07 (0.02) −0.06 (0.03)
Cohen’s d−0.29* −0.19* −0.15*
Conscientiousness
Raw difference 0.06 (0.03) 0.05 (0.03) 0.05 (0.04)
Cohen’s d0.13 0.11 0.11
Neuroticism
Raw difference −0.06 (0.03) −0.05 (0.03) −0.05 (0.04)
Cohen’s d−0.14* −0.11 −0.11
Openness to experience
Raw difference −0.07 (0.04) −0.03 (0.03) −0.01 (0.04)
Cohen’s d−0.15* −0.07 −0.01
Note: Data from 1,261 participants were included in the selection and socialization models. Dat a from 867 par tici-
pants were included in the propensity-score model. Standard errors are given in parentheses. The selection model
tested differences in the Big Five traits between the two groups at Time 1. The socialization model tested these
differences at Time 2, controlling for all personality traits at Time 1. The propensity-score model equated the two
groups on social environmental and psychological variables at Time 1. All reported values are based on pooled
estimates across multiple imputations.
*p < .05.
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Military Training and Personality Development 5
p > .05). These results suggest that military training is associ-
ated with changes in agreeableness.
To provide a more stringent test of the effect of military train-
ing on personality, we next ran a propensity-score analysis, in
which we controlled for a large number of potentially confound-
ing covariates (Table 1). As in the previous analysis, results
showed that military recruits had lower levels of agreeableness
than individuals who chose civilian community service (d =
−0.15, p < .05). The similar effect size between this more strin-
gent analysis and the covariate regression model suggests that
the effect of military training on agreeableness is robust and not
likely due to unmeasured preexisting differences.
Does the effect of military training persist?
We next tested whether differences in agreeableness persisted
after military recruits and participants who chose civilian
community service went to college or entered the labor force.
A second-order latent growth model was fit to a subsample of
participants who were assessed four times over a 6-year time
span. This subsample was matched on the propensity score at
baseline following the procedure used in the previous set of
analyses.
The base model fit well, χ2(112, N = 539) = 162.4, compara-
tive fit index = .98, root-mean-square error of approximation =
0.03. Significant variance existed around the slope parameter,
suggesting that people changed at different rates or in different
directions across the four waves. A dummy variable in which
civilian community service was set to 0 and military training
was set to 1 was included to test the long-term effects of military
training. As Figure 1 shows, military recruits had significantly
lower levels of agreeableness 4 years after completing military
training (at Time 4) than did young adults who participated in
civilian community service (b = −0.16, SE = 0.04, p < .05). Sim-
ilarly, the slope for agreeableness over time was shallower for
military recruits than for people who chose civilian community
service (b = −0.04, SE = 0.01, p < .05). Together, these results
Table 2. Mean Personality Trait Ratings and Standardized Change Scores of
the Two Groups
Personality trait and group Time 1 Time 2 Cohen’s d
Extraversion
Civilian community service 2.80 (0.40) 2.83 (0.42) −0.07
Military service 2.81 (0.39) 2.84 (0.42) −0.07
Agreeableness
Civilian community service 2.89 (0.35) 3.00 (0.35) 0.32*
Military service 2.79 (0.36) 2.87 (0.40) 0.21*
Conscientiousness
Civilian community service 2.84 (0.47) 2.98 (0.48) 0.33*
Military service 2.90 (0.44) 3.08 (0.41) 0.39*
Neuroticism
Civilian community service 2.17 (0.41) 2.01 (0.47) −0.36*
Military service 2.11 (0.44) 1.92 (0.47) −0.39*
Openness to experience
Civilian community service 2.70 (0.46) 2.76 (0.46) 0.14
Military service 2.63 (0.42) 2.68 (0.44) 0.11
Note: The civilian-communit y-service group consisted of 1,016 participants, and the
military-ser vice group consisted of 245 participants. Standard deviations are given in
parentheses. Participants were assessed during their final year of high school, prior
to conscription (Time 1), and then, on average, 2 years later (Time 2). All values are
based on pooled estimates across multiple imputations.
*p < .05.
Measurement Point
Agreeableness
2.75
2.80
2.85
2.90
2.95
3.00
3.05
3.10
●
●
●
●
●
●
●●●●
Time 1Time 2
Civilian-Community-Service Group
Military-Service Group
Time
3T
ime 4
Fig. 1. Linear-growth-model estimates of agreeableness as a function of
time of measurement and group. The initial assessment occurred during
participants’ final year of high school, prior to conscription (Time 1), and
the follow-up assessments (Time 2–Time 4) were completed on average at
2-year intervals.
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6 Jackson et al.
indicate that military training is still associated with changes in
agreeableness after military service is completed and partici-
pants enter college and the labor market.
Discussion
The study reported here is the first to examine the relation
between military training and the development of personality
traits. Results indicated that personality traits play an impor-
tant role in military training. First, personality traits prospec-
tively influenced who chose to join the military, as individuals
lower in agreeableness, neuroticism, and openness to experi-
ence were more likely to enter military service. Second, mili-
tary training was associated with changes in agreeableness.
These changes were not temporary, as military recruits contin-
ued to display lower levels of agreeableness than people who
chose civilian community service even after both groups
entered college and the labor market. These findings are espe-
cially notable, as no prior study has used propensity-score
matching to identify life experiences associated with changes
in personality traits.
In both military recruits and people who chose civilian
community service, changes in personality traits resulted in
greater maturity, as defined by increases in conscientiousness
and agreeableness, and decreases in neuroticism (Caspi et al.,
2005). Thus, the maturation often attributed to military train-
ing (e.g., Dar & Kimhi, 2001) may actually be best ascribed to
the specific time period of young adulthood. However, even
though both military recruits and people who chose civilian
community service increased in maturity-related traits, mili-
tary recruits were significantly lower in agreeableness than
people who chose civilian community service after training.
Given that this difference persisted after military training was
completed, the results of our study suggest that military
recruits are not “late bloomers” who eventually catch up in
levels of agreeableness but, instead, continue to be less agree-
able after entering the civilian world. Given that lower levels
of agreeableness are associated with greater levels of conflict
in romantic relationships, difficulties in getting along with
friends, and aggression (Ozer & Benet-Martinez, 2006;
Wilkowski, Robinson, & Meier, 2006), our findings suggest
that military training may be potentially detrimental. How-
ever, lower levels of agreeableness are not completely nega-
tive, as they also predict greater occupational attainment (Ozer
& Benet-Martinez, 2006).
Lower levels of agreeableness are likely to be especially
beneficial in a military context. For example, aggressive
behavior has long been associated with the training of soldiers,
as a number of aggression-related skills (e.g., marksmanship)
constitute specific training goals. Given that aggression is
associated with lower levels of agreeableness, higher levels
of agreeableness may interfere with effective training and
performance. Indeed, individuals with higher levels of agree-
ableness are slower and less likely to react aggressively after
being presented with aggression cues (Meier, Robinson, &
Wilkowski, 2006). Thus, soldiers who are higher in agreeable-
ness may not react quickly in life-or-death situations. In this
view, lower levels of agreeableness are likely beneficial for
soldiers and do not necessarily reflect low levels of maturity.
The current findings are especially intriguing because per-
sonality traits are highly consistent and, therefore, difficult to
change (Roberts & Jackson, 2008). Despite the many studies
that have identified changes in personality traits (e.g., Jackson
et al., 2009; Lüdtke et al., 2009), few studies have attempted to
identify the specific experiences associated with such changes
(Roberts et al., 2008). The studies that have are fraught with
selection biases resulting from their observational design,
whereas in the study reported here, we attempted to control for
these biases using propensity-score matching. Moreover, past
studies have examined changes in personality traits across
experiences that vary from person to person (e.g., work expe-
riences; Roberts, Caspi, & Moffitt, 2003). The current study
was unique, however, in that we focused on changes in person-
ality traits across participants who had very similar experi-
ences: For example, military training is uniform in time (i.e.,
all subjects are conscripted for the same duration) and in con-
tent (e.g., all military recruits are expected to meet the same
standards and are given the same performance reviews).
Accordingly, the results reported here constitute some of the
best evidence to date that changes in personality traits are
associated with social experiences.
Although the current study used a large sample and
employed advanced methods to investigate changes in person-
ality traits, these findings must still be considered in light of
some limitations. For example, despite the relatively large
sample size, there still may be questions concerning the gener-
alizability of these results. Given that our sample consisted of
students on an upper-level track in the German educational
system, our results may not apply to students on lower-level
tracks. Similarly, selection effects may differ in countries
without conscription. Moreover, even though we attempted to
control for selection biases, the observational nature of the
study’s design prohibits strong conclusions to be drawn;
unmeasured confounds may still exist.
Although a number of studies have found increases in agree-
ableness during young adulthood (e.g., Vaidya, Gray, Haig,
Mroczek, & Watson, 2008), a number of them have not
(Roberts, Walton, & Viechtbauer, 2006); this suggests the pos-
sibility that civilian community service was responsible for
increases in agreeableness. However, although not every study
has found normative changes in agreeableness, our results must
be interpreted with respect to the sample we used. Past analyses
of this data set found a normative trend toward increases in
agreeableness for all individuals (both males and females;
Lüdtke et al., 2009). Moreover, individuals who did not partici-
pate in either military or civilian community service had levels
of agreeableness that were more similar to people who chose
civilian community service than to military recruits. These
at WASHINGTON UNIV LIBRARY on January 25, 2012pss.sagepub.comDownloaded from
Military Training and Personality Development 7
findings suggest that changes in agreeableness were likely a
response to military service, not to civilian community service.
It is possible, however, that the experiences driving our
results did not occur in the military. That is, military experi-
ences may not affect the development of agreeableness.
Instead, differences in agreeableness may be attributable
to an absence of important developmental experiences
within military service. Future research on the mechanisms
responsible for these changes is needed to tease apart these
different interpretations. Moreover, future research needs to
examine the reasons why some studies have found changes
in agreeableness during young adulthood, whereas others
have not.
In conclusion, our results suggest that personality traits play
an important role in military training. We found evidence for
both selection and socialization effects. Individuals who eventu-
ally chose military training had lower levels of neuroticism,
agreeableness, and openness to experience than individuals
who chose civilian community service. Moreover, participation
in military training was associated with changes in agreeable-
ness. As agreeableness is associated with important life out-
comes, military training may impair some aspects of the lives of
soldiers even if they never engage in combat. Overall, it thus
appears that the man makes the military and the military makes
the man.
Acknowledgments
We would like to thank Brent Roberts for comments on an earlier
draft of this manuscript.
Declaration of Conflicting Interests
The authors declared that they had no conflicts of interest with
respect to their authorship or the publication of this article.
Supplemental Material
Additional supporting information may be found at http://pss.sagepub
.com/content/by/supplemental-data
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