Happiness nose dives as you hit middle age - but only if you live in the affluent West, according to experts.
Using world survey data, the Lancet study authors found life satisfaction followed a predictable trajectory depending on where people lived.
In countries such as the UK and the US, life satisfaction followed a U-shape, dipping to a low in midlife.
In Africa it was low throughout, and in Eastern Europe, the former Soviet Union and Latin America it declined with age.
The reasons behind the trends were multiple and complex, but there were some plausible explanations as well as important lessons to be learned, said Prof Andrew Steptoe, of University College London, and colleagues.
dip：動詞，下降。例句：House prices dipped in the first three months of the year.（今年前3個月房價下跌。）
predictable：形容詞，可預期的、意料之中的、老套的。例句：The ending to the film was just so predictable.（這部電影的結局真老套。）
plausible：形容詞，可信的；名詞plausibility，可信度。例句：In Chapter 2 she goes on to test the plausibility of these assumptions.（在第二章裡，她繼續檢驗這些假說的可信度。）