twoway_fpfitci.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 fpfitci}{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 33 35 2}{...}
{p2col :{hi:[G] graph twoway fpfitci} {hline 2}}Twoway fractional-polynomial prediction plots with CIs{p_end}
{p2colreset}{...}


{title:Syntax}

{p 8 55 2}
{cmdab:tw:oway}
{cmd:fpfitci}
{it:yvar} {it:xvar}
{ifin}
{weight}
[{cmd:,}
{it:options}]

{p2colset 9 31 33 2}{...}
	{it:options}{col 31}description
	{hline 70}
	{it:{help twoway_fpfit:fpfit_options}}{...}
{col 31}estimation command and options
	{cmd:level(}{it:#}{cmd:)}{...}
{col 31}confidence level for CI of mean
	{cmd:nofit}{...}
{col 31}prevent plotting the prediction

	{cmdab:fitp:lot:(}{it:{help graph_twoway:plottype}}{cmd:)}{...}
{col 31}how to plot fit; {cmd:line} default
	{cmdab:cip:lot:(}{it:{help graph_twoway:plottype}}{cmd:)}{...}
{col 31}how to plot CI; {cmd:rarea} default

	{it:{help cline_options}}{...}
{col 31}change look of predicted line
	{it:{help area_options}}{...}
{col 31}change look of CI

INCLUDE help gr_axlnk

INCLUDE help gr_twopt
	{hline 70}
{pin}
Option {cmd:level()} is {it:rightmost}; {cmd:nofit}, {cmd:fitplot()},
and {cmd:ciplot()} 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:fpfitci} calculates the prediction for {it:yvar} based on
estimation of a fractional polynomial of {it:xvar} and plots the resulting
curve along with the confidence interval of the mean.


{title:Options}

{phang}
{it:fpfit_options}
    refers to any of the options of {cmd:graph} {cmd:twoway} {cmd:fpfit};
    see {helpb twoway fpfit}.
    These options are rarely specified.

{phang}
{cmd:level(}{it:#}{cmd:)}
    specifies the confidence level, in percent, for the confidence
    interval of the mean; see {helpb level}.

{phang}
{cmd:nofit}
    prevents the prediction from being plotted.

{phang}
{cmd:fitplot(}{it:plottype}{cmd:)}
    is rarely specified.  It specifies how the prediction is to be plotted.
    The default is {cmd:fitplot(line)}, meaning that the prediction will be
    plotted by {cmd:graph} {cmd:twoway} {cmd:line}.
    See {helpb graph twoway} for a list of {it:plottype} choices.
    You may choose any plottypes that expect a single {it:y} variable and a
    single {it:x} variable.

{phang}
{cmd:ciplot(}{it:plottype}{cmd:)}
    specifies how the confidence interval is to be plotted.  The
    default is {cmd:ciplot(rarea)}, meaning that the prediction will be
    plotted by {cmd:graph} {cmd:twoway} {cmd:rarea}.

{pmore}
    A reasonable alternative is {cmd:ciplot(rline)}, which will
    substitute lines around the prediction for shading.
    See {helpb graph twoway} for a list of {it:plottype} choices.
    You may choose any plottypes that expect two {it:y} variables and one
    {it:x} variable.

{phang}
{it:cline_options}
     specify how the prediction line is rendered;
     see {it:{help cline_options}}.
     If you specify {cmd:fitplot()}, then rather than using {it:cline_options},
     you should select options that affect the specified {it:plottype}
     from the options in {help scatter}.

{phang}
{it:area_options}
     specify how the confidence interval is rendered; see 
     {it:{help area_options}}.
     If you specify {cmd:ciplot()}, then rather than using {it:area_options},
     you should specify whatever is appropriate.

INCLUDE help gr_axlnkf

INCLUDE help gr_twoptf


{title:Remarks}

{pstd}
Remarks are presented under the headings

	{help twoway fpfitci##remarks1:Typical use}
	{help twoway fpfitci##remarks2:Advanced use}
	{help twoway fpfitci##remarks3:Cautions}
	{help twoway fpfitci##remarks4:Use with by()}


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

{pstd}
{cmd:twoway} {cmd:fpfitci} by default draws the confidence interval
of the predicted mean:

	{cmd:. sysuse auto, clear}

	{cmd:. twoway fpfitci mpg weight}
	  {it:({stata "gr_example auto: twoway fpfitci mpg weight":click to run})}
{* graph gtfpfitci1}{...}

{pstd}
If you specify the {cmd:ciplot(rline)} option, the confidence interval will be
designated by lines rather than shading:

	{cmd:. twoway fpfitci mpg weight, ciplot(rline)}
	  {it:({stata "gr_example auto: twoway fpfitci mpg weight, ciplot(rline)":click to run})}
{* graph gtfpfitci2}{...}


{marker remarks2}{...}
{title:Advanced use}

{pstd}
{cmd:fpfitci} can be usefully overlaid with other plots:

	{cmd:. sysuse auto, clear}

	{cmd:. twoway fpfitci mpg weight || scatter mpg weight}
	  {it:({stata "gr_example auto: twoway fpfitci mpg weight || scatter mpg weight":click to run})}
{* graph gtfpfitci3}{...}

{pstd}
Note that in the above graph, the shaded area corresponds to the 95%
confidence interval for the mean.

{pstd}
It is of great importance to note that we typed

	{cmd:. twoway fpfitci} ... {cmd:|| scatter} ...

{pstd}
and not

	{cmd:. twoway scatter} ... {cmd:|| fpfitci} ...

{pstd}
Had we drawn the scatter diagram first, the confidence interval would
have covered up most of the points.


{marker remarks3}{...}
{title:Cautions}

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

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

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

{pstd}
See {hi:Cautions} in {helpb twoway lfitci}.


{marker remarks4}{...}
{title:Use with by()}

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

	{cmd}. twoway fpfitci  mpg weight  ||
		 scatter  mpg weight  ||
	  , by(foreign, total row(1)){txt}
	  {it:({stata "gr_example auto: twoway fpfitci mpg weight || scatter mpg weight || , by(foreign, total row(1))":click to run})}
{* graph gtfpfitci4}{...}


{title:Also see}

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

{psee}
Online:  
{helpb twoway lfitci},
{helpb twoway qfitci};
{helpb twoway fpfit};
{helpb fracpoly}
{p_end}