METHODS: the model of extended linear expenditure system (ELES) was used to analyze the data from the third health service investigation in the city of Ningbo.
方法：数据来源于宁波市第三次卫生服务调查资料，采用扩展线性支出系统模型。
ELES (Extended Linear Expenditure System) is a good demand model which has explicit economic meaning and is used extensively.
扩展的线性支出系统需求函数模型是一类经济意义清楚，具有广泛应用价值的需求函数模型。
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