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	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

In reply

Hutchinson and Lebedev have chosen to ignore an essential paragraph on page 1058 of our article. With respect, we quote part of it here again: "It is difficult to demonstrate directly that a group of individuals constitute a cluster in time and space with respect to a disease. In addition to the obvious problem of ascertainment bias associated with the retrospective identification of such groups and the difficulty of defining a suitable control framework for the purposes of comparison, there is a major logical barrier to our attempt to prove the hypothesis that the group constitutes a meaningful cluster."

Hutchinson and Lebedev proceed to argue that "only outliers" have been examined. It is, of course, only the outliers under an assumed distribution that suggest to a researcher the possibility of a mixture of distributions. Ignoring the information contained in extreme outliers may be costly. For example, 2 planes . . . [Full Text of this Article]

AUTHOR INFORMATION

Ajit Kumar, DM; Susan Calne, CM; Michael Schulzer, MD, PhD; Edwin Mak, BSc; Zbigniew Wszolek, MD; Chris Van Netten, MD; Joseph K. C. Tsui, MD, FRCPC; A. Jon Stoessl, MD, FRCPC; Donald B. Calne, DM, FRSC

RELATED ARTICLE

On the Use of Clusters to Determine Environmental Influence on Disease
Michael Hutchinson and Sergey Lebedev
Arch Neurol. 2005;62(2):331.
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