In studying geographic disease distributions, one normally compares rates among arbitrarily defined geographic subareas (for example, census tracts), thereby sacrificing the geographic detail of the original data. The sparser the data, the larger the subareas must be in order to calculate stable rates. This dilemma is avoided with the technique of density equalizing map projections (DEMP). Boundaries of geographic subregions are adjusted to equalize population density over the entire study area. Case location plotted on the transformed map should have a uniform distribution if the underlying disease rates are constant. The present report describes the application of the DEMP technique to 401 childhood cancer cases occurring between 1980 and 1988 in four California counties, with the use of map files and population data for the 262 tracts of the 1980 Census. A kth nearest neighbour analysis provides strong evidence for geographic non-uniformity in tract rates (p < 10(-4)). No such effect is observed for artificial cases generated under the assumption of constant rates. Work is in progress to repeat the analysis with improved population estimates derived from both 1980 and 1990 Census data. Final epidemiologic conclusions will be reported when that analysis is complete.

California↗

PubMedDate not supplied

Genetic marker determination in evidence bloodstains: the effect of classification errors on probability of non-discrimination and probability of concordance.

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Blood Stains↗

PubMedDate not supplied

Assessing combined chemical exposures as risk factors for neural tube defects.

Many studies have investigated whether chemical exposures early in pregnancy increase risks to women of delivering offspring with congenital anomalies. We investigated whether periconceptional exposures to chemicals in combination increased risks to women of having neural tube defect (NTD)-affected pregnancies. Women were asked about occupational tasks performed during the periconceptional period. These tasks were assigned by an industrial hygienist to a priori defined exposure categories. The exposure categories included 74 chemical groups. Two population-based case control studies were analyzed. Information on tasks was obtained from mothers of 538 NTD cases and their 539 controls in one study, and mothers of 265 NTD cases and 481 controls from another study. We used data from the first study to identify clues. Specifically, we estimated NTD risks for maternal occupational exposures to all possible pairs, triplets, and quadruplets of 74 chemical groups. Chemical combinations revealing elevated NTD risks in these "clue generation" analyses were then investigated in the second population-based case-control study for their contribution to risk of NTDs. We computed odds ratios for each of the total 192,374 possible comparisons and identified all combinations that produced odds ratios of 5 or more. A 5-fold elevated risk criterion revealed 53 combinations. These 53 reflected various combinations of exposures exclusive to 12 of 74 chemical groups. Analyses of data from the second study did not identify odds ratios of 2.0 or greater for maternal exposures to the 12 chemical groups that resulted in 5-fold elevated risks in the first study. Despite the use of a labor-intensive method to categorize exposures, we were unable to substantiate clues associated with combined chemical exposures identified in one large case-control study as NTD risk factors in a second case-control study.

Adult↗

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Detection of excess disease near an exposure point: a case study.

Many studies have evaluated the likelihood of adverse health effects associated with environmental contamination from point source exposures. Two statistical measures used in these studies are the ratio, R, of the observed to the expected number of cases occurring in the area containing the point and the average distance, D, between the cases and the point. This paper estimates the probability of detecting an association between disease and exposure when one actually exists (power) for R and D for several specific and plausible statistical models. Results are presented in the context of rare diseases such as congenital malformations. The practical implications of using these measures for the evaluation of risk of disease in environmental epidemiologic investigations are discussed.

California↗

PubMedDate not supplied

Exposure misclassification due to residential mobility during pregnancy in epidemiologic investigations of congenital malformations.

This study addressed the question of how maternal migration between conception and birth affects estimates of risk in studies of congenital malformations when movement is related to the exposure. For example, in studying the potential association between proximity to a chemical waste site and the occurrence of birth defects, incorrect inferences might be drawn if maternal residence at birth was used as a surrogate for exposure at conception in the case when a significant amount of media attention influenced some women to move away from the site after becoming pregnant. A simple statistical model is proposed that defines the distance to a fixed exposure point measured at birth as a function of the distance to the point measured at conception, the probability of movement, the direction of movement, and the distance moved. Bias is the difference between the expected results when distance is measured at birth versus conception. The amount of bias can be substantial for movement patterns that may be likely to occur. This simplified model was used in an effort to explore and better understand the relationships between maternal migration and risk.

Abnormalities, Drug-Induced↗

PubMedDate not supplied

Race, socioeconomic status, and prostatic cancer.

Using mortality and incidence data from Alameda County, California, this study attempted to determine whether the higher occurrence rate of prostatic cancer among black men as compared with whites in the United States might be explained by racial differences in factors associated with socioeconomic status. Each death or case of prostatic cancer was assigned to a social class based on census tract of residence, and rates by race and socioeconomic status were computed. Comparison of age-specific mortality and incidence rates by socioeconomic status reveals no gradient in either whites or blacks. The higher risk for blacks holds up at almost every age and socioeconomic level. However, the racial differences are less pronounced for incidence than for mortality. Racial differences in the occurrrence of deaths appearing in Part II of the death certificate are also examined.

Age Factors↗