twoway_lowess.hlp

是一个经济学管理应用软件 很难找的 但是经济学学生又必须用到

{smcl}
{* 08apr2005}{...}
{cmd:help twoway lowess}{right:dialogs:  {dialog twoway_overlay:overlaid twoway}{space 0}}
	{right:{dialog twoway_simple:single twoway}{space 2}}
{hline}

{title:Title}

{p2colset 5 32 34 2}{...}
{p2col :{hi:[G] graph twoway lowess} {hline 2}}Local linear smooth plots{p_end}
{p2colreset}{...}


{title:Syntax}

{p 8 32 2}
{cmdab:tw:oway}
{cmd:lowess}
	{it:yvar}
	{it:xvar}
	{ifin}
	[{cmd:,}
	{it:options}]

{p2colset 9 31 33 2}{...}
	{it:options}{col 31}description
{p2line}
	{cmdab:bw:idth:(}{it:#}{cmd:)}{...}
{col 31}smoothing parameter
	{cmdab:m:ean}{...}
{col 31}use running-mean smoothing
	{cmdab:now:eight}{...}
{col 31}use unweighted smoothing
	{cmdab:lo:git}{...}
{col 31}transform the smooth to logits
	{cmdab:a:djust}{...}
{col 31}adjust smooth's mean to equal {it:yvar}'s mean

INCLUDE help gr_clopt

INCLUDE help gr_axlnk

INCLUDE help gr_twopt
{p2line}


{title:Description}

{pstd}
{cmd:graph} {cmd:twoway} {cmd:lowess} plots a lowess smooth of {it:yvar} on
{it:xvar} using {cmd:graph} {cmd:twoway} {cmd:line}.


{title:Options}

{phang}
{cmd:bwidth}{cmd:(}{it:#}{cmd:)}
    specifies the bandwidth.  {cmd:bwidth(.8)} is the default.
    Centered subsets of {it:N}*{cmd:bwidth()} observations, {it:N} = number of
    observations, are used for calculating smoothed values for each point in
    the data except for end points, where smaller, uncentered subsets are
    used.  The greater the {cmd:bwidth()}, the greater the smoothing.

{phang}
{cmd:mean}
    specifies running-mean smoothing; the default is running-line
    least-squares smoothing.

{phang}
{cmd:noweight}
    prevents the use of Cleveland's (1979) tricube weighting function; the
    default is to use the weighting function.

{phang}
{cmd:logit}
    transforms the smoothed {it:yvar} into logits.

{phang}
{cmd:adjust}
    adjusts by multiplication the mean of the smoothed {it:yvar} to equal the
    mean of {it:yvar}.  This is useful when smoothing binary (0/1) data.

{phang}
{it:cline_options}
     specify how the lowess line is rendered and its appearance;
     see {it:{help cline_options}}.

INCLUDE help gr_axlnkf

INCLUDE help gr_twoptf


{title:Remarks}

{pstd}
{cmd:graph} {cmd:twoway} {cmd:lowess} {it:yvar xvar} uses the {cmd:lowess}
command{hline 2}see {helpb lowess}{hline 2}to obtain a local linear smooth of
{it:yvar} on {it:xvar} and uses {cmd:graph} {cmd:twoway} {cmd:line} to plot
the result.

{pstd}
Remarks are presented under the headings

	{help twoway lowess##remarks1:Typical use}
	{help twoway lowess##remarks2:Use with by}


{marker remarks1}{...}
{title:Typical use}

{pstd}
The local linear smooth is often graphed on top of the data, possibly
with other regression lines:

	{cmd:. sysuse auto, clear}

	{cmd:. twoway scatter mpg weight, mcolor(*.6) ||}
	{cmd:         lfit    mpg weight    ||}
	{cmd:         lowess  mpg weight}
	  {it:({stata "gr_example auto: twoway scatter mpg weight, mcolor(*.6) || lfit mpg weight || lowess mpg weight":click to run})}
{* graph gtlowess1}{...}

{pstd}
Notice our use of {cmd:mcolor(*.6)} to dim the points and thus make the
lines stand out; see {it:{help colorstyle}}.

{pstd}
Notice also the {it:y} axis title:  "Mileage (mpg)/Fitted values/lowess mpg
weight".  The "Fitted values" was contributed by {cmd:twoway} {cmd:lfit} and
"lowess mpg weight" by {cmd:twoway} {cmd:lowess}.  When you overlay graphs,
you nearly always need to respecify the axes titles using the
{it:axis_title_options} {cmd:ytitle()} and {cmd:xtitle()}; see 
{it:{help axis_title_options}}.


{marker remarks2}{...}
{title:Use with by}

{pstd}
{cmd:graph} {cmd:twoway} {cmd:lowess} may be used with {cmd:by()}:

	{cmd:. use auto, clear}

	{cmd:. twoway scatter mpg weight, mcolor(*.6) ||}
	{cmd:         lfit    mpg weight ||}
	{cmd:         lowess  mpg weight ||, by(foreign)}
	  {it:({stata "gr_example auto: tw scatter mpg weight, mcolor(*.6) || lfit mpg weight || lowess mpg weight ||, by(foreign)":click to run})}
{* graph gtlowess2}{...}


{title:Also see}

{psee}
Manual:  {bf:[G] graph twoway lowess}

{psee}
Online:  
{helpb lowess};
{helpb twoway mspline}
{p_end}