Income and the incidence of oral cavity cancer: cross-national study.

Objective: To examine the relation between income and oral cancer incidence in countries at different stages of economic development.
Design: Descriptive study with regression analysis of oral cancer incidence in relation to real gross domestic product (GDP) per capita from 1970 to 2000 performed for 8 different countries.
Methods: GDP per capita was collected from the United States, Hong Kong, Singapore, Italy, Mexico, Philippines, Poland, and Romania. Correlation factor and Pearson values were compared.
Results: The association between income and the oral cavity cancer rate was significant in all the countries selected. Using linear regression analysis, the results showed high r2 value. The increase of real GDP correlated negatively with the rate of male oral cavity cancer in the United States, Italy, Hong Kong, and Singapore but not in Mexico, Philippines, Poland, and Romania.
Conclusions: The association between incidence and income appears to depend on per capita GDP, being negative in countries with GDP above US$10,000 and positive in countries with GDP below US$10,000.