Open-SOEP: Cohort vs. Age Effects on Personality

The German Socio-Economic Panel (SOEP) is a unique and amazing project. Since 1984, representative samples of German families have been survived annually. This project has produced a massive amount of data and hundreds of publications. The traditional journal publications make it difficult to keep track with developments and to find related articles. A better way to make use of these data may be open science where researchers can quickly share information.

In 2005, the SOEP included a brief, 15-item, measure of the Big Five personality traits. These data were used for cross-sectional studies that related personality to other variables measured in the SOEP such as well-being (Rammstedt, 2007). In 2009, the SOEP repeated the measurement of the Big Five. This provided longitudinal data for analyses of stability and change of personality. Researchers rushed to analyze the data and to report their findings. JPSP published two independent articles based on the same data (Lucas & Donnellan, 2011; Specht, Egloff, Schmukle, 2011). Both articles examined age-differences across birth-cohorts and over time. Ideally age-effects would show up in both analyses and produce similar trends in the data. Both articles also paid little attention to cohort differences in personality (i.e., Germans born in 1920 who grew up during Nazi times might differ from Germans born in 1950 who grew up during the revolutionary 60s).

In 2017, the Big Five questions were administered again, which makes it easier to spot age-trends and to distinguish age-effects from cohort effects. Recently, the first article based on the three-waves of data was published in JPSP (Wagner, Lüdtke, & Robitzsch, 2019). The article focused on retest correlations (consistency of individual differences over time), and did not examine mean levels of personality. The article does not mention cohort effects.

Cohort/Culture Effects

Like many Western countries, German culture has changed tremendously during the 20st century. In addition, German culture has been shaped by unique historical events such as the rise and fall of Hitler, the second world war, followed by the Wirschaftswunder, the division of the country into a democratic and a socialist country and the unification of Germany after the fall of the Berlin Wall. The SOEP data provide a unique opportunity to examine whether personality is shaped by culture.

So far, studies of cultural influences on personality have mostly relied on cross-cultural comparisons of Western cultures with non-Western cultures. The main finding of these studies is that citizens of modern, individualistic nations tend to be more extraverted and open to experiences than citizens in traditional, collectivistic cultures.

Based on these findings, one might expect higher levels of extraversion and openness in younger generations of Germans who grew up in a more individualistic culture than their parents and grandparents.

Method

The data are the Big Five ratings for the three waves in the SOEP (vp, zp, & bdp). Data were prepared and analyzed using R (see OSF for R-code). The three items for each of the Big Five scales were summed and analyzed as a function of 7 cohorts spanning 10 years (born 1978 to 1988 age 17-27 to age 77 to 87) and three waves (2005, 2009, 2013). The overall mean was subtracted from each of the 21 means and the mean differences were divided by the pooled standard deviation. This way, mean differences in the figures are standardized mean differences to ease interpretation of effect sizes.

Results

Openness to Experience

Openness to experience showed a clear cohort effect (Figure 1) with the lowest scores for the oldest cohort (1918-28) and the highest scores for the youngest cohort (1978 to 1988). The difference between the youngest and oldest cohorts is d = .72, which is considered a large effect size. In comparison, there is no clear age trend in Figure 1. While, scores decrease from t1 to t2, they increase from t2 to t3. All differences between t1 and t2 are small, |d| < .2.

Extraversion

Extraversion also shows a cohort effect in the predicted direction, but the effect size is smaller, d = .34.

In contrast, there are no age effects and the overall difference between 2005 and 2013 is d = -0.01.

Conscientiousness

I next examined conscientiousness because studies of age effects tend to show the largest age effects for this Big Five dimension. Regarding cohort effects, one might expect a decrease because older generations worked very hard to rebuild post-war Germany.

Consistent with the developmental literature, the youngest age-cohort shows an increase in conscientiousness from 2005 to 2013, although the effect size is small (d = .21). The other age-cohorts show very small decreases in conscientiousness except for the oldest age-cohort that shows a small decrease, d = -.22. Regarding cohort effects, there is no general tend, but the youngest cohort shows very low levels of conscientiousness even in 2013 when they are 25 to 35 years old.

Agreeableness

Developmental studies suggest that agreeableness increases as people get older. However, the SOEP data do not confirm this trend.

Within each cohort, agreeableness scores decrease although the effect sizes are very small. The overall decrease from 2005 to 2013 is d = -.09. In contrast, there is a clear cohort effect with agreeableness being the highest in the oldest generation. The decrease tends to level of for the last three generations. The effect size is moderate, d = -.38.

Neuroticism

The main result for neuroticism is that there is neither a pronounced cohort effect, d = -.09, nor age effect, d = -.13.

Conclusion

Previous analysis of personality data in the SOEP have focused on age effects and interpreted cross-sectional differences between older and younger Germans as age effects. However, these analyses were based on only two waves of data, which makes it difficult to interpret changes in personality scores over time. The third wave shows that some of the trends did not continue and suggest that there are no notable effects of aging in the SOEP data. The only age-effect consistent with the literature is an increase in conscientiousness in the youngest cohort of 17 to 27-year olds.

However, the data are consistent with cohort effects that are consistent with cross-cultural studies. The more individualistic a culture becomes, the more open and extraverted individuals become. Deeper analysis might help to elucidate which factors contribute to these changes (e.g., education level). The results also suggested that agreeableness decreased which might be another consequence of increasing individualism.

Overall, the results suggest that personality is influenced by cultural factors during adolescence and early adulthood, but that personality remains fairly stable throughout adulthood. This conclusion is also supported by other longitudinal studies (e.g., MIDUS) that show little changes in Big Five scores over time. Maybe Costa and McCrae were not entirely wrong when they compared personality to plaster that can be shaped while it is setting, but remains stable after it is dried.

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