def H0(mean_tuple, z_tuple = None, significance = 5):
	"""
	Accept or reject the null hypothesis H0

	Parameters
	----------
	> mean_tuple: a tuple containing means before and after intervention (mu, muI)
	> z_tuple: a tuple contianing values of (z, z_star)
	Provide any one of the required tuples. 
	> significance: the minimum difference between the means for accepting the null

	Returns
	-------
	True -> if it retains the null
	False -> if it rejects the null
	"""
	
	if z_tuple:
		z, z_star = z_tuple
		if abs(z) > abs(z_star):
			# mean lies within the critical region
			return False  # reject the null
		return True  # accept the null
	
	# else, for mean-tuple
	mean, meanI = mean_tuple
	if abs(mean-meanI) > 5:
		return True  # accept the null
	return False