help for bidensity

Bivariate kernel density estimation

bidensity
varnameY
varnameX
[if exp]
[in range]
[, n(#)
kernel(kernelname)
xwidth(#)
ywidth(#)
saving(name)
replace
nograph scatter[(scatter_options)]
contourline_options
mname(name)

Description

bidensity produces bivariate kernel density estimates and graphs the result using a contourline plot.
The default kernel is an Epanechnikov.

Options

n(#) specifies the number of points on the Y- and X-axes at which the density estimate is to be evaluated. The default is min(_N,50).

kernel(kernelname) specifies which kernel should be used. The default is epanechnikov.
Other options are gaussian, rectangle, triangle, and epan2.
These kernels are bivariate products of the univariate kernels described in kdensity.

xwidth(#) specifies the halfwidth of the kernel, the width of the density window around each point of varnameX.
If xwidth() is not specified, then the "optimal" width is used; see kdensity.

ywidth(#) specifies the halfwidth of the kernel, the width of the density window around each point of varnameY.
If ywidth() is not specified, then the "optimal" width is used; see kdensity.

saving(name) saves the density estimates to name.dta, along with the x and y point values at which the density is estimated.
If the file already exists, the replace option must be used to overwrite the previous data. The density estimates are saved in the variable "_d".

scatter[(scatter_options)] superimposes a twoway scatter graph of varnameY and varnameX on the contourline graph of the density estimates.

contourline_options are options to modify the contourline graph.

nograph specifies that the contourline graph should not be drawn.

mname(name) is a stub name for retaining the Mata matrices containing the density estimates ("name_d"), the X axis grid values ("name_x"), and the Y axis grid values ("name_y").
If mname is specified, these matrices can be seen after the bidensity with the command mata: mata describe.

Examples

. webuse grunfeld, clear

. gen linv = log(invest)

label var linv "Log[Investment]:. label var linv "Log[Investment]"

. gen lmkt = log(mvalue)

. label var lmkt "Log[Mkt value]"

. bidensity linv lmkt

. bidensity linv lmkt, n(100)

. bidensity linv lmkt, xw(.5) yw(.5)

. bidensity linv lmkt, scatter levels(10)

. bidensity linv lmkt, saving(biden) replace

. bidensity linv lmkt, mname(bid)

. mata: mata describe

Authors

John Luke Gallup, Portland State University, USA

jlgallup@pdx.edu

Christopher F. Baum, Boston College, USA

baum@bc.edu

Also see

On-line: kdensity