Studies from 10nations reveal that the rates of depression among women are twice as high as they are among men.Do women have a biological bent for depression，or are social double standards the major cause？
Mental health workers have long noticed among the clinically depressed women take up a bigger proportion.Until recently，though，it was unclear whether more women than men were ill or，instead，whether more women sought help.In fact，a mounting collection of studies has confirmed that major depression is twice as common among women as it is among men.’This is one of the most consistent findings we have ever had，’says Myrna M.Weissman of Columbia University.
Scientists searching for explanations are challenged by the fact that a variety of cues prompt depression in different people.Sorting out which factors might have a greater influence on women has not proved easy.Both sexes stand an equal chance of inheriting major depression，so genes are most likely not to blame.Yet hormones and sleep cycles--which differ dramatically between the sexescan alter mood.Also，many workers have proposed that social discrimination might put women under high levels of stress.
In 1990an international group examines mood disorders.In the 10nations reviewed so far，the team has found that among generations reaching maturity after 1945，depression seems to be on the rise and occurs at a younger age.Although overall incidence varies regionally，’everywhere the rates of depression among women are about twice as high as they are among men，’Weissman says.
In contrast，lifetime rates for manic-depressive illness do not differ according to sex or culture.Mark S.George and his colleagues at the National Institute of Mental Health （NIMH）recently studied which regions of the brain have greater blood flow during periods of depression.George found that ’the brain activity of the men and women of depression looked very different.’He has since compared feelings of anger，anxiety and happiness，finding no such big a difference.
Because one in five American women has a history of depression，especially as they often pursue therapy from other sources，sometimes on top of an anti-depressant clinic.Says Leibenluft：’It is remarkable how little work has been done on this subject.’

Which one of the following is true about Myrna M.Weissman’s comment？（）