为了支持他们自己所发表的声明，作者(指芝加哥大学的那两个教授)编制了12个收入群体的价格指数，在编制的过程中他们利用了官方的数据和详细的关于不同家庭消费习惯的私人信息。
To back these claims up, the authors constructed price indices for 12 income groups, using official figures and detailed private information on the spending habits of different households.
Malthus论证说，自然群体的数量是呈指数级增长的，而食物供应的增加却是呈线性的。
Malthus argued that natural populations grow at an exponential rate, whereas the increase in food supply is linear.
积极的态度是会传染的。和积极的人相处，积极的态度会让整个群体的动力指数迅速增长。
Positive attitudes are contagious. Connect with other positive people. Multiple positive attitudes lead to exponential motivation as a group.
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