1. Social, Economic and Housing Statistics Division; US Census Bureau; Washington DC 20233 MD USA
2. Department of Agricultural Economics; Purdue University; West Lafayette IN 47907 USA
3. Department of Spatial Economics; VU University and Tinbergen Institute; Amsterdam The Netherlands
4. Department of Spatial Economics; VU University Amsterdam; Amsterdam the Netherlands
5. National Institute of Demographic and Economic Analysis; University of Waikato; Hamilton 3240 New Zealand