People's personalities can change considerably over time, say scientists, suggesting that leopards really can change their spots. Psychologists from The University of Manchester and London School of Economics and Political Science (LSE) also showed that small positive personality changes may lead to greater increases in happiness than earning more money, marrying, or gaining employment.

The study, published in the journal Social Indicators Research, should be of interest to British Prime Minister David Cameron, who has suggested that a measure of the nation's 'happiness' was a better guide to how the country was performing than Gross Domestic Product (GDP) alone.

Lead author Dr Chris Boyce, from the University of Manchester's School of Psychological Sciences, said: "We found that our personalities can and do change over time -- something that was considered improbable（不大可能的） until now -- and that these personality changes are strongly related to changes in our wellbeing.

"Compared with external factors, such as a pay rise, getting married or finding employment, personality change is just as likely and contributes much more to improvements in our personal wellbeing."

Previous studies have shown that personality accounts for up to 35% of individual differences in life satisfaction, compared to just 4% for income, 4% for employment status and between 1% and 4% for marital status. However, because it was believed our personalities were fixed, policies to improve wellbeing have focused on these lower-impacting external factors.

Dr Boyce said: "Our research suggests that governments could measure 'national personality'; for example, whether the population is becoming more extroverted（性格外向的） , conscientious（认真的） , open to experience, and agreeable, and how this links to national events.

"Fostering the conditions where personality growth occurs -- such as through positive schooling, communities, and parenting -- may be a more effective way of improving national wellbeing than GDP growth."