def confidence_ellipse_area(signal):
	""" Returns area of the 95 perc. confidence ellipse"""

	s_AP = np.std(signal[1])
	s_ML = np.std(signal[0])
	s_AP_ML = 1./signal.shape[1]*np.sum((signal[0]-np.mean(signal[0]))*(signal[1]-np.mean(signal[1])))
	area = 2*np.pi*3.0*np.sqrt(s_AP**2*s_ML**2-s_AP_ML**2)
	return area