def threshold(data):
	"""
	Threshold: measure of how scattered the sign is (deviation).
	
	Parameters
	----------
		data: array-like
			2D matrix of shape (time, data)
		
	Returns
	-------
		thresholdData: 1D numpy array containing the total threshold value for a 
				 given signal
	
	Reference
	---------
		Guillén, P., Martínez-de-Pisón, F., Sánchez, R., Argáez, M., & Velázquez, L. (2011). 
		Characterization of subcortical structures during deep brain stimulation utilizing 
		support vector machines. Conference Proceedings: Annual International Conference of 
		the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine 
		and Biology Society. Annual Conference, 2011, 7949–7952.
	"""
	
	i = data-(sum(data)/len(data))
	j = sum(i*i)
	
	thresholdData = (3*(j**(1/2)))/(len(data)-1)
	
	return thresholdData