A method of assessing the extent to which the value of a variable on a given segment of a network influences values of that variable on contiguous segments is examined here. The method uses network autocorrelation analysis, a network variant of spatial autocorrelation analysis, and Moran's I statistic to make the assessment. Illustrations of positive and negative network autocorrelation are given and interpreted for several simple linear networks. An empirical sampling distribution for the case of a ten link network is derived based on 100,000 samples; this distribution is compared with a normal distribution and found not to be significantly different. Use of network autocorrelation analysis with more complex networks is demonstrated using 1991 motor vehicle accident rates for a portion of the motorway network of Belgium. A significant level of positive network autocorrelation is observed. It is further demonstrated that the source of the observed positive covariation can be identified using a secondary analysis that focuses on the motorway and ring road components of the overall system to identify those portions of the network that are the major sources of the positive autocorrelation. A further analysis reveals that the major sources of this positive covariation have been properly identified. (A)
Abstract