合成不确定度的自由度

合成不确定度（或方差估计）的自由度在直接测量量独立和不独立时并不相同．本文以二元函数ｚ＝ｆ（ｘ，ｙ）为例，讨论了ｚ及其最佳估计的不确定度（或方差估计）的自由度，以及一些在教学中容易碰到的与自由度有关的问题，如求合成方差估计的两种方法（直接法和误差传播公式法）等．给出直接测量量多于两个时结果不确定度的自由度公式．

The Degree of Freedom of Combined Uncertainty

In this peper, it is shown that combined uncertainties(or variance estimates) in indirect measurements have different number of degree of freedom to independent and dependent direct measured quantities. A bivariable function z=f(x,y) is used as an example in our discussion.It is That the degree of freedom of uncertainties(or variance estimates) of z and its best estimate z =f(x,y) is investigated at independent x, y and dependent x,y respectively. In the end of the paper, two formulae of the degree of freedom of uncertainties of z and z are also given in the case of more than two direct maseured quantities.