Major depressive disorder's association with altitude of residence by county in the United States for 2012

Depression is a leading cause of disability worldwide and is often associated with suicide. Recent studies have shown that altitude of residence is a predictor of suicide rates in the United States when controlling for gun ownership and population density. Altitude at the substate level has also been shown to be a risk factor for completed suicide in bipolar disorder. In addition, the incidence of major depressive disorder (MDD) correlates with altitude of residence. This study seeks to further explore this relationship and hypothesizes that altitude of residence at the county level will have a significant correlation with incidence of MDD when controlling for gun ownership, population density and socioeconomic status. The CDC's 2012 Behavioral Risk Factor and Surveillance System (BRFSS) provides data on depression rates, county of residence, education level, income level, and gender. The 2004 BRFSS provides the best firearm ownership data. Altitude of residence is calculated by county from the Shuttle Radar Topography Mission (SRTM) data set developed by the National Geospatial-Intelligence Agency and NASA. Population density is determined by using the SRTM and the United States Census Bureau 2010 datasets. Data analysis shows that there is a significant difference between the mean altitude of those who have ever been told they have a depressive disorder (mean=1450, sd=1786) and those who have not (mean=1422, sd=1796) (t=3.84, df=115560, p<0.001). The final model comparing these two groups accounts for gun ownership, population density, gender, and socioeconomic status. This warrants further studies in people with depression living at higher altitudes.