普遍认为在发达国家人口增长的主要原因与其说是出生率的上升还不如说是由于医疗保健的改善使死亡率下降了
It is generally believed that the chief reason for the increase in population in developed countries is not so much the rise in birth rates as the decline in death rates as a result of the improvement in medical care
以上为机器翻译结果，长、整句建议使用 人工翻译 。