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, , . 1965 1991 . , 1965 8% 12% , 1991 . , . 60- 28% , . 90- 48% . , - . , , . , , , , . American Journal of Epidemiology.
90- 48% . , - . , , . , , , , . American Journal of Epidemiology.
, , , , . American Journal of Epidemiology.
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