總結一下：
作者研究平均年齡大約60歲的女性，讓她們自我評估“快樂”感。然後比較十年後的死亡率。首先，70歲低於英國女性的預期年齡，所以這期間隻有4%的人死亡。更重要的是，作者的結論並不是直接比較死亡率，而是用數據處理的方法去除了很多因素，包括研究開始時的自我健康評估，高血壓，糖尿病，哮喘，關節炎，抑鬱症，焦慮症等。最後得出的結論是這麽處理完的數據顯示死亡率和一開始的快樂評估無關。
作者認為去除這些因素是合理的，因為它們不是不快樂的結果，而是不快樂的原因。
總之，結論就是，如果把跟死亡率相關的因素都去除的話，死亡率就是相同的。什麽叫“按摩數據”，這就叫按摩數據！
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(15)01087-9/abstract
Does happiness itself directly affect mortality? The prospective UK Million Women Study
Summary
Background
Poor health can cause unhappiness and poor health increases mortality. Previous reports of reduced mortality associated with happiness could be due to the increased mortality of people who are unhappy because of their poor health. Also, unhappiness might be associated with lifestyle factors that can affect mortality. We aimed to establish whether, after allowing for the poor health and lifestyle of people who are unhappy, any robust evidence remains that happiness or related subjective measures of wellbeing directly reduce mortality.
Methods
The Million Women Study is a prospective study of UK women recruited between 1996 and 2001 and followed electronically for cause-specific mortality. 3 years after recruitment, the baseline questionnaire for the present report asked women to self-rate their health, happiness, stress, feelings of control, and whether they felt relaxed. The main analyses were of mortality before Jan 1, 2012, from all causes, from ischaemic heart disease, and from cancer in women who did not have heart disease, stroke, chronic obstructive lung disease, or cancer at the time they answered this baseline questionnaire. We used Cox regression, adjusted for baseline self-rated health and lifestyle factors, to calculate mortality rate ratios (RRs) comparing mortality in women who reported being unhappy (ie, happy sometimes, rarely, or never) with those who reported being happy most of the time.
Findings
Of 719?671 women in the main analyses (median age 59 years [IQR 55–63]), 39% (282?619) reported being happy most of the time, 44% (315?874) usually happy, and 17% (121?178) unhappy. During 10 years (SD 2) follow-up, 4% (31?531) of participants died. Self-rated poor health at baseline was strongly associated with unhappiness. But after adjustment for self-rated health, treatment for hypertension, diabetes, asthma, arthritis, depression, or anxiety, and several sociodemographic and lifestyle factors (including smoking, deprivation, and body-mass index), unhappiness was not associated with mortality from all causes (adjusted RR for unhappy vs happy most of the time 0·98, 95% CI 0·94–1·01), from ischaemic heart disease (0·97, 0·87–1·10), or from cancer (0·98, 0·93–1·02). Findings were similarly null for related measures such as stress or lack of control.
Interpretation
In middle-aged women, poor health can cause unhappiness. After allowing for this association and adjusting for potential confounders, happiness and related measures of wellbeing do not appear to have any direct effect on mortality.
Funding
UK Medical Research Council, Cancer Research UK.
