It’s a question that goes to the heart of human nature – do our personalities change through life or stay essentially the same? You might think psychology would have a definitive answer, but this remains an active research question. This is partly because of the practical challenge of testing the same group of individuals over many years. Now a major new contribution to the topic has been made available online at the PsyArXiv repository. The researchers, led by Eileen Graham at Northwestern University, have compared and combined data from 14 previously published longitudinal studies, together involving nearly 50,000 participants from the US, Europe and Scandinavia. Their findings confirm and extend existing knowledge, showing how personality traits tend to change through life in predictable ways.
Graham and her colleagues started by looking for existing long-term studies into health and ageing that had captured data on at least one of the Big Five personality traits (Openness, Conscientiousness, Extraversion, Agreeableness, Neuroticism) on at least three separate occasions among the same sample of people. Although these long-term term studies measured personality, previous investigators hadn’t necessarily looked at this aspect of their data.
Among the identified studies that met the required criteria were the Einstein Aging Study, the Midlife in the United States study, The Berlin Aging Study, The Lothian Birth Cohort and the Swedish Adoption/Twin Study of Aging. In some cases, personality data was collected from the same individuals over several decades. There was a bias in the included studies toward testing people late in life, but this helps counterbalance existing studies of lifetime personality change which have been skewed toward younger participants.
Combining data from all the studies showed that four of the five main personality traits showed statistically significant change, on average, through life, thus contradicting William James’ famous assertion that personality is set like plaster after age 30. The exception was trait Agreeableness (related to warmth and empathy), but actually this trait was found to change in each individual study, but in different directions for different studies (sometimes increasing through life, sometimes diminishing), such that it appeared stable when considered in aggregate.
Putting Agreeableness aside, the overall pattern was for the other traits to decline across the lifespan by about 1-2 per cent per decade, such that participants became, on average, more emotionally stable (save for an uptick in Neuroticism at the very end of life), but generally less outgoing, less open-minded, and less orderly and self-disciplined. This is somewhat consistent with the previously described Dolce Vita (literally “sweet life”) effect, which describes how we change in late life in response to having fewer responsibilities.
However, it’s worth reiterating that there was a bias in the included studies towards older samples. Focusing on just those studies with younger participants also provided evidence for early life increases in Conscientiousness, Extraversion and Openness (with peaks occurring in mid-life), which is consistent with another established theory known as the “maturity principle”, which states that our personalities tend to improve through life as we adapt to the growing challenges of work and family responsibilities (the observed declines in Neuroticism also fit this picture).
It’s important to remember these findings relate to sample averages, based on how personality trait levels were seen to change when data from all participants was combined. Consistent with past research, results from 12 of the 14 analysed studies revealed a good deal of individual variation in these patterns. As Graham and her colleagues put it, “not everyone changes at the same rate, or in the same direction”.
There were also some intriguing hints at how these personality dynamics might vary across cultures. Specifically, the US samples showed more marked and consistent declines in Extraversion through life compared with European samples. The researchers interpreted this as US citizens becoming less inclined with age to conform to the strong pressure in American culture to behave like an extravert.
The new findings leave many questions about personality change unanswered, such as why some people show trait changes that don’t fit with the usual pattern. However, this paper’s most important contribution is probably to show how sub-fields like this, which depend on challenging, hard-to-repeat, long-term studies, can respond to the so-called replication crisis in psychology. It’s fairly easy to re-run a simple laboratory task with students, it’s much harder to try to replicate the findings of a decades-long personality change study.
“Any one of the 14 samples used here could have comprised a publication on its own,” Graham and her colleagues explained, “with some claiming a given increase, other claiming a decrease, and still others arguing that a trait does not change at all. This has the potential to sow great confusion … However, when considered as a group with other samples, a fuller picture emerges.”
—A Coordinated Analysis of Big-Five Trait Change Across 14 Longitudinal Studies (Note this study is a preprint which has not yet been subjected to peer review)