1. In statistics, the degree of freedom refers to the number of variables with infinite values when calculating a unified measure. Usually df = n-K, where n is the sample content and k is the number of restrictive conditions or variables, or other independent statistics used in the calculation of unified measurement. The degree of freedom is usually used for sampling distribution.

2. First of all, when estimating the average of the population, the number of n in the sample is independent of each other, and any number extracted from it will not affect other data, so its degree of freedom is n ... When estimating the variance of the population, the sum of squares of deviations is used. As long as the sum of the squares of the deviations of the number n- 1 is determined, the variance is also determined; Because after determining the mean value, if the value of n- 1 is known, then the value of the nth number is also determined. Here, the average value is equivalent to a restrictive condition. With this restriction, the degree of freedom for estimating population variance is n- 1.