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This Article Extract Full Text (PDF) All Versions of this Article: AJPH.2005.079889v1 96/2/205-a    most recent Submit a response Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Austin, S. B. Articles by Gortmaker, S. L. Search for Related Content PubMed Articles by Austin, S. B. Articles by Gortmaker, S. L.

S. Bryn Austin, ScD, Steven J. Melly, MS, Brisa N. Sanchez, ScM, Aarti Patel, BA, Stephen Buka, ScD and Steven L. Gortmaker, PhD

S. Bryn Austin and Aarti Patel are with the Division of Adolescent and Young Adult Medicine, Children’s Hospital, Boston, Mass. S. Bryn Austin is also with the Department of Society, Human Development, and Health, Harvard School of Public Health, Boston. Steven J. Melly is with the Department of Biostatistics and the Department of Environmental Health, Harvard School of Public Health; Brisa N. Sanchez is with the Department of Biostatistics; and Stephen Buka and Steven L. Gortmaker are with the Department of Society, Human Development, and Health, Harvard School of Public Health.

Correspondence: Requests for reprints should be sent to S. Bryn Austin, ScD, Division of Adolescent and Young Adult Medicine, Children’s Hospital, 300 Longwood Ave, Boston, MA 02115 (e-mail: bryn.austin{at}childrens.harvard.edu).

We thank Spielman for commenting on our article and giving us an opportunity to continue the dialogue on methodological issues in studying food environments. In response to his point about network versus straight-line distances, we would like to note that in a related study, our research team found network and straight-line distances in Chicago to be highly correlated, and results did not differ when models were tested with network versus straight-line distances. Chicago streets follow a fairly dense grid, which may explain why a difference was not found between the 2 methods.

That said, Spielman has identified an aspect of spatial analyses that needs more methodological development. ArcGIS software¹ will calculate network distances, but it is only as good as the available network data. For instance, street network data generally available for geocoding addresses do not indicate barriers to pedestrians, such as a divided roadway with limited pedestrian crossings.

In response to Spielman’s comment about zoning regulations affecting land-use patterns, we would like to clarify that our analyses and the reported confidence intervals were not based on an assumption of complete spatial randomness of restaurants throughout Chicago. Rather, simulations used to generate confidence intervals were based on a null hypothesis of spatial randomness of restaurants relative to the spatial location of schools. We too were interested in examining the potential importance of zoning regulations, so we repeated our spatial analyses within strata defined by degree of commercialization. As reported in our article, we found evidence of clustering within areas of the city characterized by high and moderate levels of commercialization.

Taking a step back from the details of the statistical methods, an observation we would add to the discussion is that rather than overestimating the availability of unhealthful food in school neighborhoods, our study is very likely to have underestimated it. Our fast-food database did not include convenience stores, corner stores, gas station food markets, and vending machines that offer children access to an abundance of inexpensive, calorie-dense food of low nutritional value. Future work that includes these additional food outlets in characterizing food environments in school neighborhoods may in fact paint a more dismal nutritional picture than our study did.

Reference

1. ArcGIS 8.3 [computer program]. Version 8.3. Redlands, Calif: Environmental Systems Research Institute Inc; 2003.

This Article Extract Full Text (PDF) All Versions of this Article: AJPH.2005.079889v1 96/2/205-a    most recent Submit a response Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Austin, S. B. Articles by Gortmaker, S. L. Search for Related Content PubMed Articles by Austin, S. B. Articles by Gortmaker, S. L.