In mathematics, "marginal" just means a derivative.
As for elasticity, take the price elasticity of demand for example, it is a measure of how "responsive" demand is to some change in price or income. It is defined to be the percent change in quantity divided by the percent change in price. In symbols the definition of elasticity is
. Where q is the quantity, p is the price.
Hence elasticity can be expressed as the ratio of price to quantity multiplied by the slope of the demand function.
From the formulas we can see clearly that the concepts of "marginal" and "elasticity" are different.
As for elasticity, take the price elasticity of demand for example, it is a measure of how "responsive" demand is to some change in price or income. It is defined to be the percent change in quantity divided by the percent change in price. In symbols the definition of elasticity is
Hence elasticity can be expressed as the ratio of price to quantity multiplied by the slope of the demand function.
From the formulas we can see clearly that the concepts of "marginal" and "elasticity" are different.
其实这个问题在我初学经济学时也在困扰着我，究竟(dy/Y)/(dx/X)或者说d(InY)/d(Inx)与变化率dy/dx相比有何优势？我在查过百科之后依然百思不得其解，最后我在一个PPT里才发现弹性的意义，那就是相对变化率。例如同样是变化，1000元的商品甲涨1元的涨价幅度和10元的商品乙涨1元的涨价幅度是不一样的，即商品甲涨了0.1%，商品乙涨了10%。显然，在这里绝对改变量dx和绝对变化率dy/dx是不能说明全部信息的，所以我们需要研究相对改变量dy/Y以及相对变化率(dy/Y)/(dx/X)
另外，理解弹性的意义是非常重要的，例如不理解弹性是不可能理解柯布—道格拉斯生产函数的。
另外，理解弹性的意义是非常重要的，例如不理解弹性是不可能理解柯布—道格拉斯生产函数的。