Our methodology was evaluated by means of a numerical case study. We constructed artificial clusters using a map consisting of 203 hexagonal cells arranged in a regular grid, 15 of which are structural zeros. An example can be seen in Fig. 1 . Gray regions indicate the ''true'' cluster while the )'s indicate structural zeros. We compare the Poisson, ZIP and ZIP'EM scans in terms of power, sensitivity and positive predictive value (PPV). The Scan-ZIP and Scan-ZIP'EM methods presented systematically and significantly better results when compared to the Scan-Poisson, as shown in Table 1 for the given cluster of Fig. 1 . More examples and a real data application will also be presented.