Degrees of Freedom

A good understanding of degrees of freedom (df)is important in statistics, but most statistics textbooks do not really explain what it means. In most cases, degrees of freedom are thought of as a parameter used to define statistical distributions and conduct [Page 258]hypothesis tests. For instance, the sampling distribution for the t statistic is a continuous distribution called the t distribution. The shape of the t distribution depends on one parameter, the degrees of freedom. In a sample of size n, the t distribution has n − 1 df.

Degrees of freedom can be thought of in other ways also. The degrees of freedom indicate the number of independent pieces of information that are allowed to vary in a system. A simple example is given by ...