Population densities in relation to bladder cancer mortality rates in America from 1950 to 1994
Previous studies have reported that bladder cancer risks are elevated in industrial and urban areas. The cause is believed to be the result of occupational exposure from industries located in urban areas. Recent studies suggest that traffic air pollution may also increase bladder cancer risks. The study purpose is to investigate the relationship between bladder cancer mortality and population density of counties in America. Another objective is to explore traffic air pollution and industrial exposures as risk factors. Bladder cancer mortality rates for white men and women from 1950 to 1994 and population densities (population per 10 square miles) of 2,248 counties were the basis of the study. A linear regression analysis was performed to evaluate the relationship between bladder cancer mortality rates and population densities after log transforming the population density data set. In addition, the counties were divided into quartiles based on bladder cancer mortality rates. Mean population density values with 95% confidence intervals for the quartiles were computed. Correlation coefficients (R) between bladder cancer mortality rates and the population densities were R = .37, P < .001 for men and R = .28, P < .001 for women. In addition, population densities increased with increasing bladder cancer mortality rates across all quartiles. The mean population density of the highest quartile was more than ten times higher than the lowest. In this study, we found a strong association between bladder cancer mortality and population density. Traffic air pollution is a potential cause.