People really can change, according to a new study by researchers at the University of California at Berkeley.

The researchers studied 132,515 adults age 21 to 60 on the personality traits known as the "Big Five": conscientiousness, agreeableness, neuroticism, openness and extraversion.

They found that people's personalities can change after age 30. The results are published in the May issue of the Journal of Personality and Social Psychology.

The findings contradict the popular belief that personality traits are genetically programmed to stop changing by early adulthood.

The researchers reported that conscientiousness increased throughout the age range studied, with the biggest increases in a person's 20s. This trait is defined as being organized, planful, and disciplined, and past research has linked it to work performance and work commitments.

Agreeableness increased the most during a person's 30s; this trait is defined as being warm, generous, and helpful, and has been linked to relationships and to prosocial behavior. Neuroticism, which is defined in people who worry and are emotionally unstable, declined with age for women but did not decline for men. Openness showed small declines with age for both men and women. And extraversion declined for women, but did not show changes in men.

Both neuroticism and extraversion scores were higher for younger women than for younger men. But for both of these traits -- and most strikingly for neuroticism -- the apparent sex differences diminished with age.

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