8.124 Why called “degrees of freedom”? You know the sample mean x of n observations. Once you know 1n - 12 of the observations, show that you can find the remaining one. In other words, for a given value of x, the values of 1n - 12 observations determine the remaining one. In summarizing scores on a quantitative variable, having 1n - 12 degrees of freedom means that only that many observations are independent. (If you have trouble with this, try to show it for n = 2, for instance showing that if you know that x = 80 and you know that one observation is 90, then you can figure out the other observation. The df value also refers to the divisor in s2 = Σ1x - x22> 1n - 12.)