Abstract: A method of computing statistics relating to the flow of data by way of a packet-switched data transmission system wherein a packet includes path address data and network address data, and the network includes means, such as an RMON1 matrix table, for providing traffic flow data indexed according to each of a plurality of traffic flow paths identified by the path address data. Data packets are sampled and, for each of a multiplicity of packet types indexed according to selected address data within the packets, traffic flow counts are respectively incremented in response to each new sample data packet of the respective type. For each traffic flow path indicated in sample packets a respective one of a plurality of reference traffic flow counts is incremented in response to each new relevant sample data packet. Values corresponding to said traffic flow data are stored for each of the traffic flow paths for which said reference traffic flow counts are accumulated.