The Science Behind Personality

At some point in your life, you've probably filled in a personality questionnaire ("Do you see yourself as ... ?"), and wondered as you ticked the boxes if there can really be any validity to such a simplistic way of assessing people. Surely the scores just reflect your mood on the day, or what you want the investigator to think. Surely everyone gives the same answer, which is "it depends." Or even if the scores measure something, surely it is how the person sees themselves, rather than how they actually are.

In a new book, I examine what the extent of the science underlying personality psychology really is. The answer is: more than you would think. While it has always been popular in business and pop psychology, and within academic psychology, personality research has been a poor relation to the parts of the discipline with experiments and hard objective measures. However, this is changing fast. The field of personality is undergoing a renaissance.

The reasons for the renaissance are several. Academics now have some really good long-term studies of the same individuals, and it turns out that those brief, simplistic, pencil-and-paper questionnaires have surprisingly useful properties. They produce a wide range of self-descriptions. The responses are fairly repeatable over intervals of many years. They also correlate quite well with ratings of the person given by their spouse, friends or colleagues.

Much more importantly, though, the responses turn out to predict objective events. For example, in a famous cohort of gifted Californian children recruited in the 1920s, and who are elderly or deceased now, personality "scores" -- numerical representations of answers to questions -- are significant predictors of life expectancy. In another long-term study, this time of American married couples, the quality and duration of the marriage is predicted by the personality scores of both parties prior to marriage.

There are many other examples, with personality scores predicting substance addiction, problem gambling, and the onset of psychological illnesses. Of course the prediction is a statistical one -- you can assign odds, not make oracular pronouncements -- but this is how it always is in psychology. Humans are such complex systems that you are happy to explain a portion of the variation in outcomes, and never expect to explain it all.

In recent years there has been renewed interest in personality assessment. This has been greatly aided by the fact that there is now a consensus on what the key variables are. Its early development, the field was greatly hampered by every investigator having his or her own scales, often using different names and measures for what turned out to be the same thing, or indeed the same names for what turned out to be different things.

But over the last 20 years, many studies in several different cultures have shown that much of the systematic variation in personality can be reduced to scores along five dimensions (the "Big Five"): Extraversion, Neuroticism, Conscientiousness, Agreeableness, and Openness. It's important to stress that these are all continuous dimensions. That is, there are no discrete "types" of person. Personality dimensions are like height or weight, which vary continuously, not like being a left- or a right-hand writer. Your score on one dimension is independent of your scores on all the others, so there is an almost infinite diversity of different overall profiles possible.

If developments within psychology have facilitated the renaissance of personality studies, it is at the interface with biology where the exciting developments are beginning to come. Neuroscientists have shown, mainly using the increasingly sophisticated brain imaging techniques that are now available, that those simple pencil-and-paper personality scores correlate significantly with the size or neurophysiological reactivity of specific regions of the brain.