Lack of time-space clustering of childhood leukemia in Los Angeles County, 1960-1964.
Andrew G. Glass, Nathan Mantel · PubMed · 1969
Dates and residence data for 298 Los Angeles childhood leukemia deaths during the period 1960–64 were analyzed for time-space clustering by 2 approaches. By the Knox approach, 2 cases are considered to be close neighbors if they are within both a specified spatial and a specified temporal distance of each other. A wide spectrum of critical distances, both for time and space, was used in identifying close neighbors. By the Mantel approach, a correlation- or regression-type analysis is made to see if the reciprocal of the spatial separation between any 2 cases is related to the reciprocal of the absolute temporal separation. The latter approach requires increasing each separation by a suitable additive constant prior to taking reciprocals, and for this purpose a wide spectrum of additive constants was employed relative to each type of separation. Significance tests for both approaches were made by the permutational procedure described by Mantel. This procedure permits one to obtain the expectation and variance of the statistics yielded by either the Knox or Mantel approach under all possible random pairings of the reported dates of death and places of residence. The analyses revealed no significant or suggestive indication of time-space clustering, whether applied to deaths at age 0–14, 0–5, or 2–9 years. The absence of clustering is interpreted as suggesting that, if leukemia is due to an infectious agent, then it is one to which humans are highly resistant. Some interesting insights were obtained from the behavior of the statistical procedures employed.