Black and mixed-ethnic Britons are less satisfied with their lives on average than the UK population as a whole, a survey suggests.
Some 80,000 people across the UK,polled by the Office for National Statistics,produced an average life satisfaction rating of 7.4 out of 10.
But black Britons averaged 6.6, while mixed-ethnic Britons scored 6.9.
The survey, in April to September 2011, was part of the ONS's ongoing Measuring National Well-being Programme.
The average rating for life satisfaction was also lower than the national figure for those of Pakistani origin - 7 out of 10 - and Bangladeshis - 7.1.
The four questions posed by the survey also included one seeking ratings for people's overall happiness, with answers nationwide producing an average of 7.3 out of 10.
Again, black Britons reported the lowest level of happiness - 6.9 on average - followed by mixed-ethnic and Pakistani respondents, with both of those groups averaging 7 out of 10.
Indians, Chinese and people of other Asian backgrounds produced similar scores to the national average.
BBC home editor Mark Easton said: "The reasons for these results are not easy to pin down."
Possible factors were the "income, education or employment patterns within different ethnic groups" and "an element of discrimination or prejudice", he said.
"But equally it may that there are cultural differences in the way people respond to questions from pollsters," he added.
The questions, included in ONS's annual population survey, were:
- Overall, how satisfied are you with your life nowadays?
- Overall, to what extent do you feel that the things you do in your life are worthwhile?
- Overall, how happy did you feel yesterday?
- Overall, how anxious did you feel yesterday?
People responded with ratings on a scale between 0 and 10, where 0 indicated "not at all" and 10 meant "completely".
Breaking down the responses nationally, Northern Ireland residents expressed the highest level of satisfaction - 7.6 - compared with 7.5 for Scotland and 7.4 for both England and Wales.
ONS also categorised the data by marital status and found married people were the most satisfied on average, with a score of 7.7 out of 10.
That compared with: 7.5 for people co-habiting with a partner; 7.3 for single people; 6.8 for widowed people; 6.6 for divorcees.
Meanwhile, people with children rated their lives as more worthwhile: parents of two children averaged 7.9 out of 10; those with one child scored 7.7; those with no offspring scored 7.6.
People reported higher levels of well-being at the ends of the age range - 16 to 19, and 65 to 79 - than those in their middle years, the research also found.
"Happiness is smile-shaped for decades," said our correspondent. "We tend to be relatively contented in our youth and become progressively grumpy into middle-age before recovering our sense of humour as our hair turns grey."
The New Economics Foundation (NEF) think tank said ONS research had to take into account respondents' income patterns, since other well-being studies had found "a clear link between happiness and earnings".
"Well-being measures give us a new understanding of the lives of different population groups, with black Britons and the unemployed, for example, having particularly low well-being," said NEF senior researcher Juliet Michaelson.
"The challenge now is to understand what is driving these considerable differences, but income data remains the missing piece of the puzzle."
The Measuring National Well-being programme was launched in November 2010.
Following public consultation on which measures to use to assess well-being, the ONS is due to publish its first full set of findings this July.
The programme aims to "provide a fuller understanding of how society is doing than economic measures, such as GDP", the ONS says.
"The ONS measurement programme is key to giving people a say in the areas affecting their lives - in health, employment, crime, education and skills."
The findings can then be considered by policy-makers to see how proposals would impact on people's well-being, the ONS suggests.