The activity index is intended to help all members get a better idea of how active another XING member is and how quickly they’re likely to a respond to a message, for instance. It’s also a way of seeing if XING is a good way to contact someone. A member’s activity index is measured on the basis of the frequency and regularity of their activity. It will drop if they’re only occasionally on XING or have stopped using it for a while altogether. At the moment, mobile XING usage via out apps has no influence on the activity index.