Ferrari and Robertson add that "it is not always clear if the I(D)/I(G) ratio should be the ratio of the peak heights or peak areas. Generally, groups using BWF+Lorentzian fits report peak height ratios, while groups using two Gaussians report the area ratio. The difference is not so important for disordered graphite, as the peak widths are similar, but this is not so for amorphous carbons. In that case, -Ferrari and Robertson explain -the broadening of the D peak is correlated to a distribution of clusters with different orders and dimensions, and thus the information about the less distorted aromatic rings is in the intensity maximum and not in the width, which depends on the disorder. Ring orders other that six tend to decrease the peak height and increase its width" . I(D)/I(G) as the ratio of peak heights is mainly used by Ferrari and Robertson in their three-stage model, by means of which we can see how the position of the G peak changes and the D peak appears.