Race, Income, Urbanicity, and Asthma Hospitalization in California: Statistical AnalysisUsing bivariate and multivariate techniques, this study examined differences in asthma hospitalizations among and between different racial/ethnic, sex, age, and income groups statewide and in Los Angeles. Statewide, rates of hospitalization for asthma were examined by age group (<5 years, 5 to 19 years, 20 to 34 years, and 35 to 64 years), gender, and race/ethnicity (white, black, Hispanic, and Asian). Rates of asthma hospitalization by race/ethnicity group were age adjusted using the entire California statewide population as the reference group.

A small area analysis of the rates of asthma hospitalization in California as a whole and in Los Angeles was conducted using three-digit zip code areas. To explicate the relationship between asthma morbidity and socioeconomic status, the rate of hospitalization was calculated for the three-digit zip code areas within each median household income quartile for California overall and for Los Angeles. Mantel’s adjusted test of trend was used to examine if the risk of asthma hospitalization declined with increasing income.
Using a statistical procedure (SAS general linear models), multiple ordinary linear regression models were used to determine the extent to which median household income, race/ ethnicity, and urbanicity explained geographic variations in asthma hospitalization rates statewide. The dependent variable was the three-digit zip code area hospitalization rates for persons in each of the four age groups. The independent variables were area-level measures of median household income, percentage of the population that was black, Hispanic, and Asian, and urbanicity. A separate model that included an interaction term for race (percentage of the population black) and median household income was also estimated for each age category . Log transformations were applied to normalize the dependent and independent variables.
Finally, an analysis of bicoastal differences in asthma hospitalization rates was conducted by comparing rates of hospitalization in Los Angeles (derived in this analysis) to published rates obtained from an earlier study of asthma hospitalization rates in New York City. In this New York City analysis, Carr et al calculated asthma rates of hospitalization among New York City residents aged 0 to 34 years by dividing the number of hospital discharges from data obtained from the New York State Department of Health by the total number of New York City residents (overall and by age, gender, and race/ethnicity) from data obtained from the 1980 US Bureau of the Census Summary Tape File 3B.