Use of a density equalizing map projection in analysing childhood cancer in four California counties.

In this study, 401 cases of childhood cancer in four California counties in 1980-1988 were analysed with the innovative methodology of density equalizing map projections. The data were originally collected and analysed by the California State Department of Health Services (DHS). In addition to the new analytic technique, the present analysis used population data more detailed and more accurate than those in the DHS analysis. The geographic boundaries of the 259 census tracts in the study area were adjusted according to population at risk so as to make population density everywhere constant; then the 401 case locations were plotted on the density equalized map. If risk is everywhere equal, the resulting distribution of cases should be uniform except for statistical variation. The metric used was a measure of the variability of the density of cases on the density equalized map. The same metric was calculated for independent samples of artificial cases, generated under the null hypothesis of equal risk. The slight geographic non-uniformity observed among the real cases is well within the limits of variation observed in the samples of artificial cases. In agreement with results published by DHS, we conclude that there is no evidence for geographic variation of risk among the cases studied. Subsets of the data, selected by age, sex, race, time period and cancer site, yielded similar negative results.

Breast cancer detection: maps of 2 San Francisco Bay area counties.

OBJECTIVES: This study describes the incidence of late-stage and in situ breast cancer among White women, using specialized mapping techniques that reflect incidence adjusted for the population at risk, and applies these maps to characterize areas with high and low risk of breast cancer. METHODS: Data from the Surveillance, Epidemiology, and End Results (SEER) database and the US Census Bureau were used to study the geographic distribution of breast cancer at the census-tract level in 2 San Francisco Bay Area counties for the years 1978 through 1982. Sociodemographic characteristics of areas with high and low incidence of the stage-specific disease were compared by means of a linear discriminant function. RESULTS: For late-stage breast cancer, the most important variables in discriminating high-risk from low-risk areas were college education, percentage of residents over age 65, and median income. The strongest ecologic indicators of high risk for in situ breast cancer were median income and percentage unemployed. CONCLUSIONS: This study demonstrates the usefulness of census tracts and sociodemographic measures of income and education in describing in situ and late-stage breast cancer.

Use of density equalizing map projections (DEMP) in the analysis of childhood cancer in four California counties.

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.

Interfacing U.S. census map files with statistical graphics software: application and use in epidemiology.

In 1990, the United States Bureau of the Census released detailed geographic map files known as TIGER/Line (Topologically Integrated Geographic Encoding and Referencing). The TIGER files, accessible through purchase or federal repository libraries, contain 24 billion characters of data describing various geographic features including coastlines, hydrography, transportation networks, political boundaries, etc. for the entire United States. Many of these physical features are of potential interest in epidemiological case studies. Unfortunately, the TIGER data base only provides raw alphanumeric data; no utility software, graphical or otherwise, is included. Recently, the S statistical software package has been extended to include a map display function. The map function augments S's high-level approach towards statistical analysis and graphical display of data. Coupling this statistical software with the map data base developed for U.S. Census data collection will facilitate epidemiological research. We discuss the technical background necessary to utilize the TIGER data base for mapping with S. Two types of S maps, segment-based and polygon-based, are discussed along with methods to construct them from TIGER data. Polygon-based maps are useful for displaying regional statistical data, such as disease rates or incidence at the census tract level. Segment-based maps are easier to assemble and are appropriate when the data are not regionalized. Census tract data of AIDS incidence in San Francisco and lung cancer case locations relative to petrochemical refinery sites in Contra Costa County are used to illustrate the methods and potential uses of interfacing the TIGER data base with S.

Interpoint squared distance as a measure of spatial clustering.

The expectation and variance for the mean interpoint squared distance are presented. In order to evaluate these expressions it is necessary to calculate the moments of a bivariate uniform distribution defined over an arbitrary polygon. Expressions for these moments are presented, allowing the mean interpoint squared distance to be used as a measure of spatial clustering. The distribution and power of this test statistic is explored on the unit square, and the spatial distribution of 11 cases of non-Hodgkin's lymphoma is investigated to illustrate an application of the approach.

Distance and risk measures for the analysis of spatial data: a study of childhood cancers.

Three statistical approaches, used to detect spatial clusters of disease associated with a point source exposure, are applied to childhood cancer data for the city of San Francisco (1973-88). The distributions of incident cases of leukemia (51 cases), brain cancer (35 cases), and lymphatic cancer (37 cases) among individuals less than 21 years of age are described using three measures of clustering: distance on a geopolitical map, distance on a density equalized transformed map, and relative risk. The point source of exposure investigated is a large microwave tower located southwest of the center of the city (Sutro Tower). The three analytic approaches indicate that the patterns of the major childhood cancers are essentially random with respect to the point source. These results and a statistical model for spatial clustering are used to explore distance and risk measures in the analysis of spatial data. Both types of measures of spatial clustering are shown to perform similarly when a specific area of exposure can be defined.

Black-white differences in stage-specific cancer survival: analysis of seven selected sites.

A number of researchers have noted that the black population in the United States generally has less favorable cancer survival than does the white population. It is not clear, however, whether this difference is fully explained by differences in stage of disease at diagnosis. This study uses Surveillance, Epidemiology, and End Results program data from the San Francisco-Oakland (California) Metropolitan Statistical Area for the years 1974-1985 to study survival differences between blacks and whites while controlling for both stage and age at diagnosis. The cancer sites examined are those for which mortality is considered avoidable by early detection and treatment, namely the colon, rectum, bladder, breast, cervix, uterine corpus, and prostate. Stage-specific (local, regional, and remote) survival curves are examined for each cancer site. The site- and stage-specific curves for colon, male rectal, and prostate cancer, supplemented by proportional hazards analyses, indicate no significant stage-specific racial differentials. Stage-specific survival differentials persist for male bladder, female rectal, and breast cancer. The relation between race and stage is more complex for female bladder, cervical, and uterine corpus cancer; for these sites, there is a racial difference at some stages but not all. The consequences for secondary intervention programs are considered for the seven sites in light of these findings.

A study of multiple causes of death in California: 1955 and 1980.

Multiple cause of death patterns in California for 1980 were compared to a similar study of deaths conducted in 1955. Primary underlying causes of death changed, mainly reflecting the emergence of respiratory cancer as a major cause of death in 1980. The number of causes reported per death increased from 1955 to 1980, in all age and sex groups. Diseases of the arteries and pneumonia, which are among the most common underlying causes of death, appeared more often on death certificates in both 1955 and 1980 as contributing causes than as underlying the death. Diabetes was studied in detail in the 1955 report, and comparisons were made in 1980 to show increases in the proportions of deaths with this disease and corresponding increases in its prevalence among the living population from the National Health Survey. Multiple cause of death data can provide further information on the prevalence of a fatal disease in a population and its relative role in contributing to mortality, and can also provide new information on diseases that contribute to deaths, which was not previously available in population-based studies of single cause of death.

Density equalized map projections: a method for analysing clustering around a fixed point.

Cases plotted on a geopolitical map entail difficulties in interpretation and analysis because of variable population density in the study area. Density equalized map projections (DEMPs) eliminate the distribution of the resident population as an interfering influence by transforming map area to be proportional to population. This paper discusses a transformation algorithm, its properties, and develops statistical methods to detect clustering of cases around a fixed point for data plotted on DEMPs. We suggest two numeric methods where exact solutions are too complicated or do not exist. Finally, we illustrate these methods using data from Denver and Jefferson counties in Colorado to investigate whether lung cancer and leukaemia incidence patterns are associated with plutonium exposure from the Rocky Flats plant site.

The onset of decline in ischemic heart disease mortality in the United States.

Temporal and spatial patterns of the onset of the decline in ischemic heart disease mortality in the United States for each of the 48 contiguous US states and the District of Columbia are examined for the years 1955-1978 for age-sex-race-specific mortality. Mortality rates are derived from National Center for Health Statistics mortality data, and a polynomial interpolation is used to estimate intercensal population counts employing 1950, 1960, 1970, and 1980 US Census data. A quadratic regression equation is used to estimate the date of highest rate, which marks the beginning of the decline for each of the US states. The temporal distribution of the onset of the decline among men occurred primarily between 1960 and 1965. Among women, the onset of decline was more variable. Furthermore, strong and regular spatial patterns were seen among the groups examined and these impressions are supported by statistical analysis. California, Maryland, and the District of Columbia were early decliners in most groups studied, whereas states in the southeast were consistently among the last to experience the onset of decline. These patterns suggest the existence of an underlying phenomenon accounting for the spread or diffusion of the onset of decline in ischemic heart disease mortality.

Spatial distribution of disease: three case studies.

Maps transformed so as to have constant density of residential population were used to analyze the spatial distribution of disease in three specific areas. Each area had received recent attention because of suspected environmental pollution. The area adjacent to the Rocky Flats Facility (CO) was examined to identify any association between possible plutonium releases and increases in lung cancer or leukemia incidence. The industrial area of northern Contra Costa County (CA) was studied to explore a relationship between petrochemical industrial emissions and histologic-specific lung cancers. Finally, a suspected increase in the risk of congenital cardiac defects possibly related to pollution of the Santa Clara County (CA) water supply was investigated. No evidence of elevated risk of disease was found to be associated with either the Rocky Flats Facility or the polluted water of Santa Clara County. An increase in lung cancer, found by other investigators in earlier years, was shown to persist in association with industrial emissions in Contra Costa County.

Selected epidemiologic observations of cell-specific leukemia mortality in the United States, 1969-1977.

Utilizing a newly available data set which includes for the first time cell-specific leukemia mortality rates for the United States during 1969-1977, age and sex distributions, time trends, and geographic patterns were analyzed. Four major cell types of leukemia were considered. Acute lymphatic leukemia had a bimodal distribution with the first peak in the 5-9-year age group and lowest rates in age group 35-44, after which rates rose geometrically. Acute myeloid leukemia had only a very small childhood peak with a low in the age group 5-9, after which the rates also rose geometrically. For both chronic lymphatic and myeloid leukemia the rates rose geometrically after age 15. Rates among females were consistently lower for each age group. The highest sex ratio was found for chronic lymphatic leukemia and is proposed to be the result of a lag period between male and female rates. During the period under study acute lymphatic leukemia mortality in adults declined by almost 10% while acute myeloid leukemia mortality increased by almost 20%. Analysis of the geographic variation of the four major cell types revealed a geographic association between acute lymphatic and acute myeloid leukemia in children, a lack of association between childhood and adult cell types, and an association of acute and chronic cell types in adults.

Major histologic types of cancers of the gum and mouth, esophagus, larynx, and lung by sex and by income level.

Incidence rates by income level were computed for squamous cell carcinomas of the gum and mouth, larynx, and esophagus and for squamous cell carcinoma, small cell carcinoma, and adenocarcinoma of the lung in white males and females aged 35--64 years, with the use of data for the nine geographic areas of the Third National Cancer Survey and the 1970 U.S. census. Within sex, age, and geographic area groups, patterns of cancer incidence by income level were analyzed by use of a nonparametric statistical method. Higher rates for males than for females were found for every histologic type studied, and the ratio of male-to-female rates increased with age (especially for squamous cell carcinomas of the larynx and lung). A strong inverse relation to income level was found for all of the histologic types studied in males and for squamous cell carcinomas of the gum and mouth and esophagus and small cell carcinoma of the lung in females. These findings are discussed with reference to patterns of smoking and alcohol use by sex and social class.