j_mfxunsuit.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}
{* 04mar2005}{...}
{title:Predict expression unsuitable error message}

{pstd}
A marginal effect is a derivative of a function of the coefficients 
and independent variables of a model.
The {cmd:mfx} option {cmd:predict()} can be used to specify
the function to be differentiated. If this function depends
on quantities other than the coefficients and independent variables of the
model, {cmd:mfx} will most likely not be able to evaluate the derivative
accurately.

{pstd}
{cmd:mfx} checks for dependence on other quantities by predicting 
into different observations in the dataset and 
checking that it obtains the same value. 
If not, it determines that the expression is unsuitable.

{pstd}
The {cmd:mfx} option {cmd:diagnostics(beta)} displays the results of
these checks.  The option {cmd:force} can be used to force the calculation of
the marginal effect, although this is usually inadvisable.


{title:Examples}

{phang}{cmd:. sysuse auto, clear}{p_end}
{phang}{cmd:. regress mpg weight}{p_end}
{phang}{cmd:. mfx, predict(res) diagnostics(beta)}{p_end}

{phang}{cmd:. sysuse auto, clear}{p_end}
{phang}{cmd:. clogit for turn, group(head)}{p_end}
{phang}{cmd:. mfx, predict(pc1) diagnostics(beta)}{p_end}

{phang}{cmd:. sysuse auto, clear}{p_end}
{phang}{cmd:. xtlogit for mpg, i(rep) fe}{p_end}
{phang}{cmd:. mfx, predict(p) diagnostics(beta)}{p_end}


{title:Also see}

    Online:  {helpb mfx}

       Web:  {browse "http://www.stata.com/support/faqs/stat/mfx_unsuit.html"}