History has a long tail. Events in the distant past can have surprising effects today. For instance, past research I have blogged on has shown that autocratic rule in Qing dynasty China affects social capital today (see here), the Spanish Inquisition affects GDP in Spanish municipalities (see here), and Roman roads affect the modern location and density of roads in Europe (see here). In that vein, this recent article by Martin Obschonka (University of Amsterdam) and co-authors, published in the journal Current Research in Ecological and Social Psychology (open access), looks at the effect of Roman rule on modern incidence of personality traits and subjective wellbeing in Germany. To do this, Obschonka et al. compare people on either side of the Limes Wall, noting that:
To protect their territory with its cultural and economic advancements, the Romans built the Limes wall around 150 AD and it served as a border of the empire for more than a century. The Limes consists of three major rivers, namely the Rhine, the Danube, and the Main ("Main Limes"), as well as a physical wall ... It is well-documented that the Limes constituted a physical, economic, and cultural border between the Roman and Germanic cultures...
By comparing people on either side of the Limes Wall, Obschonka et al. try to reveal the enduring impact of Roman rule. They expect this effect on personality traits and subjective wellbeing because:
...the Roman society was much wealthier and considerably more structured and organized than the “barbaric” Germanic tribes, with an effective public administration and a relatively well-elaborated legal system... When the Romans occupied parts of the territories inhabited by Germanic tribes, they imported superior scientific knowledge and a civic structure.
To measure personality traits, Obschonka et al. turn to the German dataset from the Gosling-Potter Internet Personality Project, the largest dataset on the 'Big Five' personality traits. The German sample they use includes over 73,000 observations between 2003 and 2015, which they aggregate to regional-level averages. For subjective wellbeing (life satisfaction), they use data from the German Socioeconomic Panel between 1984 and 2016, again aggregated to regional-level averages. They also look at life expectancy. Using a simple OLS regression model, with a 'treatment variable' indicating that a region was in the Roman occupied area, Obschonka et al. find that:
...the populations in those regions that were occupied by the Romans nearly 2000 years ago show significantly higher levels of extraversion, agreeableness, and openness, and significantly lower levels of neuroticism (which points to more adaptive personality patterns in the former Roman regions of present-day Germany) than do the populations living in the non-occupied regions... Moreover, populations living in the formerly Roman areas today report greater satisfaction with life and health, and also have longer life expectancies...
After including a range of control variables into their models, the effects on agreeableness and openness became statistically insignificant. However, that leaves significant effects of Roman rule on extraversion and neuroticism, as well as life satisfaction and life expectancy. The results are similar when they use a spatial regression discontinuity design (RDD) instead of OLS. The spatial RDD takes account of how far away an observation is from the Limes Wall, which separates the 'treated' and 'control' regions (and regions closer to the line provide more information about the distinctive effect of the treatment, in this case Roman rule). The method assumes that places on either side of the border are similar except for the Roman occupation. This seems plausible, so the spatial RDD results in particular make the results more believable.
Obschonka et al. then turn to looking at the mechanisms that might explain the enduring effect of Roman rule. They show that:
Density of road infrastructure built by the Romans shows a statistically significant, positive effect on life and health satisfaction, as well as on life expectancy. There is a negative, statistically significant relationship with neuroticism, a positive one with extraversion, and a non-significant one with agreeableness, conscientiousness, and openness...
Running the models with the number of Roman markets and mines as the independent variable reveals a negative effect on neuroticism and a positive effect on extraversion. In addition, there is also a positive effect on conscientiousness (and openness). None of the effects on psychological well-being or health were statistically significant. Including Roman road density and the number of Roman markets and mines in the same model... clearly indicates that markets and mines are more strongly related to the personality traits, whereas Roman road density is more closely related to the health and well-being outcomes.
These results should be seen as more exploratory, but Obschonka et al. interpret them as showing:
...support for the notion that the tangible and lasting economic infrastructure built and established by the Romans left a long-term macro-psychological legacy...
Perhaps. I find it less plausible that Roman physical infrastructure had a lasting effect on modern personality traits and subjective wellbeing, and more likely that Roman worldviews and 'social infrastructure' (things like institutions or social norms, for example) was passed down from one generation to the next, showing up as a lasting effect on personality and wellbeing. Unfortunately, Obschonka et al. aren't able to tease out those sorts of mechanisms. Either way, it’s another reminder that borders drawn 2000 years ago can still show up in the data, even in places we might not think to look.
[HT: Marginal Revolution, early last year]
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