The release last week of a government-sponsored survey, the most comprehensive to date, suggests that more than half of Americans will develop a mental disorder in their lives. The study was the third, beginning in 1984, to suggest a significant increase in mental illness since the middle of the 20th century, when estimates of lifetime prevalence ranged closer 20 or 30 percent. But what does it mean when more than half of a society may suffer 'mental illness'? Is it an indictment of modem life or a sign of greater willingness to deal openly with a once-taboo subject? Or is it another example of the American mania to give every problem a name, a set of symptoms and a treatment-a trend, medical historians say, accentuated by drug marketing to doctors and patients? Changes in societies over time, and differences across cultures, make it extremely difficult to compare prevalence levels of mental illness, even today. Levels of depression in China were thought to be very low, for example, until the Harvard anthropologist Dr. Arthur Kleinman found in the 1980's that many Chinese did not think or talk about mood disorders the way Westerners do. They came to doctors or healers with physical complaints-dizziness, headaches and other pains that were treated as such, though in many cases they could be diagnosed as depression. A World Health Organization survey published in 2004 found that 2. 5 percent of Chinese reported a mood disorder in the last year, compared with a rate of 9. 6 percent in the United States. In Japan, too, reported levels of depression tend to be low-just over 3 percent reported a mood disorder in the last year, in the W. H. O. survey-in part because of a culture of stoicism, said Dr. Laurence Kirmayer, director of social and transcultural psychiatry at McGill University in Montreal. Depression, after all, is not one symptom but many, and in Japan there is strong cultural taboo against repeated, vague complaints. In addition, said Dr. Margaret Lock, a professor of social studies in medicine at McGill, Japanese doctors tend to be attentive to men's complaints of mood problems, and dismissive of women's. The result: depression rates are higher in men than in women, the reverse of the United States and much of Europe. But more than anything, historians and medical anthropologists said, the rise in the incidence of mental illness in America over recent decades reflects cultural and political shifts. 'People have not changed biologically in the past 100 years, ' Dr. Kirmayer said, 'but the culture, our understanding of mental illness' has changed. The low levels of depression in China show that_____.