Sheather, S. J. and Jones, M. C. (1991) A reliable data-based bandwidth
selection method for kernel density estimation.
Journal of the Royal Statistical Society series B
53, 683--690.
Scott, D. W. (1992)
Multivariate Density Estimation: Theory, Practice, and Visualization.
Wiley.
Wand, M. P. and Jones, M. C. (1995)
Kernel Smoothing.
Chapman & Hall.