def dof_within(samples):
	"""
	Get the degrees of freedom for within-group variability.

	Parameter
	---------
	> `samples`: a tuple of lists, where each list is a sample containing all the values of that sample

	Returns
	-------
	The degrees of freedom for within-group variability.
	"""

	k = len(samples)  # number of samples
	N = sum([len(sample) for sample in samples])
	return N - k