Using the getis statistic to explore aggregation effects in metropolitan Toronto census data

In an earlier paper by the same authors (Amrhein and Reynolds 1996), the variation of the C statistic (Getis 1991; Getis and Ord 1992) was demonstrated to correlate very highly with calculated aggregation effects. In the conclusions to this earlier paper, we called for experiments with different data sets, different aggregation rules, and different definitions of the connectivity matrix. In this paper, we explore the behaviour of census data from enumeration areas of the Toronto Census Metropolitan Area. Experiments are conducted that describe the aggregation effects that creep into the data at different scales, and the effect of the aggregation algorithm on the results. Finally, we test the ability of a modified G statistic, our Getis statistic, to predict aggregation effects.