Figure 11.12 This map shows a demographic clustering of towns in eastern Massachusetts and southern New Hampshire.

72 Towns / >

82K Subs Cluster 1AA

375K HH 22% Pen

50 Towns 137K Subs 313K HH 44% Pen

Figure 11.13 A cluster tree divides towns served by The Boston Globe into four distinct groups.

Cluster 2 contains 50 towns with 313,000 households, 137,000 of which subscribe to the daily or Sunday Globe. This level of home delivery penetration makes cluster 2 far and away the best cluster. The variables that best distinguish cluster 2 from the other clusters and from the population as a whole are home value and education. This cluster has the highest proportion of any cluster of home values in the top two bins; the highest proportion of people with 4-year college degrees, the highest mean years of education, and the lowest proportion of people in bluecollar jobs. The next best cluster from the point of view of home delivery penetration is Cluster 1AA, which is distinguished by its ordinariness. Its mean values for the most important variables, which in this case are home value and household income, are very close to the overall population means. Cluster 1B is characterized by some of the lowest household incomes, the oldest subscribers, and proximity to Boston. Cluster 1AB is the only cluster characterized primarily by geography. These are towns far from Boston. Not surprisingly, home delivery penetration is very low. Cluster 1AB has the lowest home values of any cluster, but incomes are average. We might infer that people in Cluster 1AB have chosen to live far from the city because they wish to own homes and real estate is less expensive on the outer fringes of suburbia; this hypothesis could be tested with market research.

Using Thematic Clusters to Adjust Zone Boundaries

The goal of the clustering project was to validate editorial zones that already existed. Each editorial zone consisted of a set of towns assigned one of the four clusters described above. The next step was to manually increase each zones purity by swapping towns with adjacent zones. For example, Table 11.1 shows that all of the towns in the City zone are in Cluster 1B except Brookline, which is Cluster 2. In the neighboring West 1 zone, all the towns are in Cluster 2 except for Waltham and Watertown which are in Cluster 1B. Swapping Brook-line into West 1 and Watertown and Waltham into City would make it possible for both editorial zones to be pure in the sense that all the towns in each zone would share the same cluster assignment. The new West 1 would be all Cluster 2, and the new City would be all Cluster 1B. As can be seen in the map in Figure 11.12, the new zones are still geographically contiguous.

Having editorial zones composed of similar towns makes it easier for the Globe to provide sharper editorial focus in its localized content, which should lead to higher circulation and better advertising sales.

Table 11.1 Towns in the City and West 1 Editorial Zones