To cite the \emph{ quantile } Zelig model:
 \begin{verse}
 Alexander D'Amour. 2008. "quantile: Quantile Regression for Continuous Dependent Variables" in Kosuke Imai, Gary King, and Olivia Lau, "Zelig: Everyone's Statistical Software,"\url{http://gking.harvard.edu/zelig} 
\end{verse}