Degrees of Freedom
Also called: df, degrees of freedom statistics
Degrees of freedom is the number of values in a calculation that are free to vary once constraints are imposed. Estimating a mean uses one up, which is why sample variance divides by n−1 rather than n. In regression it's observations minus parameters, and it formalises a practical warning: fit enough parameters relative to your data and the model can explain everything while knowing nothing.
Where this is taught
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