What is the finding of the leading expert in happiness as mentioned in the passage?

We may have suspected it already, but now the science backs it up: unmarried and childless women are the happiest subgroup in the population. And they are more likely to live longer than their married and child-rearing peers, according to a leading expert in happiness.
    Speaking at the Hay Festival, Paul Dolan, a professor of behavioral science at the London School of Economics, said the latest evidence showed that the traditional markers used to measure success did not correlate with happiness—particularly marriage and raising children.
    "Married people are happier than other population subgroups, but only when their spouse is in the room when they’re asked how happy they are. When the spouse is not present: miserable," he said.
    "We do have some good longitudinal data following the same people over time, but I am going to do a massive disservice to that science and just say: if you’re a man, you should probably get married; if you’re a woman, don’t bother."
    Men benefited from marriage because they "calmed down", he said. "You take less risks, you earn more money at work, and you live a little longer. She, on the other hand, has to put up with that, and dies sooner than if she never married. The healthiest and happiest population subgroup are women who never married or had children," he said.
    Dolan’s latest book, Happy Ever After, cites evidence from the American Time Use Survey (ATUS), which compared levels of pleasure and misery in unmarried, married, divorced, separated and widowed individuals. The study found that levels of happiness reported by those who were married was higher than the unmarried, but only when their spouse was in the room. Unmarried individuals reported lower levels of misery than married individuals who were asked when their spouse was not present.
    Other studies have measured some financial and health benefits in being married for both men and women on average, which Dolan said could be attributed to higher incomes and emotional support, allowing married people to take risks and seek medical help.
    However, Dolan said men showed more health benefits from tying the knot, as they took fewer risks. Women’s health was mostly unaffected by marriage, with middle-aged married women even being at higher risk of physical and mental conditions than their single counterparts.