A crude rate is simply the number of cases divided by the total population of interest. Using age-adjusted, rather than crude rates allows for a valid comparison of rates between populations that may have very different distributions of their population across age groups. Older people are much more likely to have higher incidence and mortality for most chronic degenerative diseases, including breast cancer. Age-adjustment to a 'standard population' is a statistical technique which removes the effects of age distribution and allows researchers to focus on the risk factors of interest. Rates for specific ages or groups within the population are useful for understanding the effects of breast cancer in different segments of the population.
Age is the most important risk factor accounting for breast cancer.
This discrepancy in rates may be attributable to a lack of access to health care for African American women. Incidence and mortality may not necessarily be associated or related. In the case of breast cancer in the U.S., incidence has been increasing, whereas no clear trend has been observed for mortality. The observed increase in the number of new cases may be partly attributed to recent efforts to promote early detection of breast cancer through mammography screening. The lack of a relationship between incidence and mortality is thought to be due primarily to increased early detection of tumors.