  The study of racial/ethnic inequalities in health is important to reduce the
uneven burden of disease. In the case of colorectal cancer (CRC), disparities
in survival among non-Hispanic Whites and Blacks are well documented, and
mechanisms leading to these disparities need to be studied formally. It has
also been established that body mass index (BMI) is a risk factor for
developing CRC, and recent literature shows BMI at diagnosis of CRC is
associated with survival. Since BMI varies by racial/ethnic group, a question
that arises is whether disparities in BMI is partially responsible for observed
racial/ethnic disparities in CRC survival. This paper presents new methodology
to quantify the impact of the hypothetical intervention that matches the BMI
distribution in the Black population to a potentially complex distributional
form observed in the White population on racial/ethnic disparities in survival.
We perform a simulation that shows our proposed Bayesian density regression
approach performs as well as or better than current methodology allowing for a
shift in the mean of the distribution only, and that standard practice of
categorizing BMI leads to large biases. When applied to motivating data from
the Cancer Care Outcomes Research and Surveillance (CanCORS) Consortium, our
approach suggests the proposed intervention is potentially beneficial for
elderly and low income Black patients, yet harmful for young and high income
Black populations.
