Carl Amrhein

Searching for the elusive aggregation effect: evidence from statistical simulations

The past few years have seen a resurging interest in the modifiable areal unit problem, or aggregation effects. The new evidence, however, both supports and conflicts with previous work. This paper represents the first stage in a series of numerical experiments designed to explore the nature and extent of scale and zonation effects. Results from a series of carefully controlled statistical simulations are reported. It is concluded that there definitely are aggregation effects separate from effects that can be attributed to changing the definition of the spatial process. These effects, however, vary with the statistic calculated. Means and variances are resistant to aggregation effects, whereas regression coefficients and correlation statistics exhibit dramatic effects. In summary, the world of spatial analysis as it relates to the modifiable areal unit problem is not entirely well-behaved, but neither is it completely random and ill-defined.

Making health data maps: a case study of a community/university research collaboration.

This paper presents the main findings from a collaborative community/university research project in Canada. The goal of the project was to improve access to community health information, and in so doing, enhance our knowledge of the development of community health information resources and community/university collaboration. The project built on a rich history of community/university collaboration in Southeast Toronto (SETO), and employed an interdisciplinary applied research and action design. Specific project objectives were to: (1) develop via active community/university collaboration a geographic information system (GIS) for ready access to routinely collected health data, and to study logistical, conceptual and technical problems encountered during system development; and (2) to document and analyze issues that can emerge in the process of community/university research collaboration. System development involved iteration through community user assessment of need, development or refinement of the GIS, and assessment of the GIS by community users. Collaborative process assessment entailed analysis of archival material, interviews with investigators and participant observation. Over the course of the project, a system was successfully developed, and favorably assessed by users. System development problems fell into four main areas: maintaining user involvement in system development, understanding and integrating data, bringing disparate data sources together, and making use of assembled data. Major themes emerging from the community/university collaborative research process included separate community and university cultures, time as an important issue for all involved, and the impact of uncertainty and ambiguity on the collaborative process.

The effect of data aggregation on a Poisson regression model of Canadian migration

A Statistics Canada data set for Canadian migration data at the census division level incorporating information on income tax for 1986 has already been presented. This matrix of 260 × 260 flows was used to calibrate a set of Poisson regression models by utilizing flows for the aggregate population. In this paper, the relatively high spatial resolution is used to test for aggregation effects as the original 260 units are combined to form fewer, synthetic regions with larger areas. A series of simulation experiments are performed with three different aggregation algorithms to create 130, 65, and ultimately 10 (corresponding to the provinces) synthetic regions. Average results from the experiments are compared with the original model. Results are obtained that suggest that, in this case, obvious aggregation effects similar to those observed elsewhere (by Openshaw) are not observed.