and IPR = 1/n if p i = 1/n. That is consistent with the idea of the inverse of participation by n chromophores, and also appears to be standard notation in the literature on localization phenomena. However, both Mukamel and co-workers, as well as Fleming and co-workers, are inconsistent in whether Eq. (4.18) defines the PR or the IPR. In view of the arguments above, PR should be defined as in Eq. (4.18) and its inverse, if needed, can be called 1/PR.