twoway_fpfit.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 fpfit} {right:dialogs:  {dialog erfit:easy regression fit}}
	{right:{dialog twoway_overlay:overlaid twoway}{space 4}}
	{right:{dialog twoway_simple:single twoway}{space 6}}
{hline}
{* index fits, adding}{...}

{title:Title}

{p2colset 5 31 33 2}{...}
{p2col :{hi:[G] graph twoway fpfit} {hline 2}}Twoway fractional-polynomial prediction plots{p_end}
{p2colreset}{...}


{title:Syntax}

{p 8 60 2}
{cmdab:tw:oway}
{cmd:fpfit}
{it:yvar} {it:xvar}
{ifin}
{weight}
[{cmd:,}
{it:options}]

{p2colset 9 38 40 2}{...}
	{it:options}{col 38}description
	{hline 70}
	{cmdab:estc:md:(}{it:estcmd}{cmd:)}{...}
{col 38}estimation command; default is {cmd:regress}
	{cmdab:est:opts:(}{it:fracpoly_options}{cmd:)}{...}
{col 38}options for {cmd:fracpoly} {it:estcmd}
	{cmdab:pred:opts:(}{it:predict_options}{cmd:)}{...}
{col 38}options for {cmd:predict}

	{it:{help cline_options}}{...}
{col 38}change look of predicted line

INCLUDE help gr_axlnk

INCLUDE help gr_twopt
	{hline 70}
{pin}
Options {cmd:estcmd()}, {cmd:estopts()},
and {cmd:predopts()} are {it:unique}; see {help repeated options}.

{phang}
{cmd:aweight}s,
{cmd:fweight}s, and
{cmd:pweight}s are allowed.  Weights, if specified, affect estimation but
not how the weighted results are plotted.  See {help weight}.


{title:Description}

{pstd}
{cmd:twoway} {cmd:fpfit} calculates the prediction for {it:yvar} based on
estimation of a fractional polynomial of {it:xvar} and plots the resulting
curve.


{title:Options}

{phang}
{cmd:estcmd(}{it:estcmd}{cmd:)}
    specifies the estimation command to be used;
    {cmd:estcmd(regress)} is the default.

{phang}
{cmd:estopts(}{it:fracpoly_options}{cmd:)}
    specifies options to be passed along to {cmd:fracpoly} to
    estimate the fractional polynomial regression from which the curve will be
    predicted; see {helpb fracpoly}.

{phang}
{cmd:predopts(}{it:predict_options}{cmd:)}
    specifies options to be passed along to {cmd:predict} to
    obtain the predictions after estimation by {cmd:fracpoly} {cmd:regress}.
    {cmd:predopts()} may only be used with {cmd:estcmd(regress)}.
    Predictions in all cases are calculated at all the {it:xvar} values
    in the data.

{phang}
{it:cline_options}
     specify how the prediction line is rendered; see {it:{help cline_options}}.

INCLUDE help gr_axlnkf

INCLUDE help gr_twoptf


{title:Remarks}

{pstd}
Remarks are presented under the headings

	{help twoway fpfit##remarks1:Typical use}
	{help twoway fpfit##remarks2:Cautions}
	{help twoway fpfit##remarks3:Use with by()}


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

{pstd}
{cmd:twoway} {cmd:fpfit} is nearly always used in conjunction with
other {cmd:twoway} plottypes, such as

	{cmd:. sysuse auto, clear}

	{cmd:. scatter mpg weight || fpfit mpg weight}
	  {it:({stata "gr_example auto: scatter mpg weight || fpfit mpg weight":click to run})}
{* graph gtfpfit1}{...}

{pstd}
Results are visually the same as typing

	{cmd}. fracpoly regress mpg weight
	. predict fitted
	. scatter mpg weight || line fitted weight{txt}


{marker remarks2}{...}
{title:Cautions}

{pstd}
Do not use {cmd:twoway} {cmd:fpfit} when specifying the
{it:axis_scale_options} {cmd:yscale(log)} or {cmd:xscale(log)} to create log
scales.  Typing

{phang2}
	{cmd:. scatter mpg weight, xscale(log) || fpfit mpg weight}

{pstd}
will produce a curve that will be fitted from a fractional polynomial
regression of mpg on weight rather than log(weight).


{marker remarks3}{...}
{title:Use with by()}

{pstd}
{cmd:lfit} may be used with {cmd:by()} (as can all the {cmd:twoway} plot
commands):

{phang2}
	{cmd:. scatter mpg weight || fpfit mpg weight ||, by(foreign, total row(1))}
{p_end}
	  {it:({stata "gr_example auto: scatter mpg weight || fpfit mpg weight ||, by(foreign, total row(1))":click to run})}
{* graph gtfpfit2}{...}


{title:Also see}

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

{psee}
Online:  
{helpb line},
{helpb twoway fpfitci};
{helpb twoway lfit},
{helpb twoway qfit};
{helpb twoway mband},
{helpb twoway mspline};
{helpb fracpoly}
{p_end}