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RE: st: FW: Elasticity using nlcom


From   "Martin Weiss" <martin.weiss1@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: FW: Elasticity using nlcom
Date   Mon, 7 Jun 2010 23:38:54 +0200

<>

This only deepens the mystery for me, to be honest. Why would you want to
multiply -(lagimportca-$a*laglocalca)- by zero? If you really want "...point
elasticity estimates, standard errors, test statistics, significance levels,
and confidence intervals for nonlinear combinations of parameters", why do
you not put the parameters into your -nlcom- call, but constants?


HTH
Martin

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of HENRY AKAEZE
Sent: Montag, 7. Juni 2010 22:57
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: FW: Elasticity using nlcom

Hello Martin,

Thanks for the quick reply. My globals for "a" and "b" are zeros (0).
Indeed, I intend to compute point elasticity estimates, standard errors,
test statistics, significance levels, and confidence intervals for nonlinear
combinations of parameters. The nlcom is post estimation command after using
writing and estimating an nl program in stata.

Thank you.

Henry

--- On Mon, 6/7/10, Martin Weiss <martin.weiss1@gmx.de> wrote:

> From: Martin Weiss <martin.weiss1@gmx.de>
> Subject: st: FW: Elasticity using nlcom
> To: statalist@hsphsun2.harvard.edu
> Date: Monday, June 7, 2010, 12:38 PM
> 
> <>
> 
> So Henry sent this query to me privately. I am not sure
> what his -global-s
> "a" and "b" contain, but from his second example, I think
> they represent
> scalars. Henry should think about the point of using
> -nlcom-: "nlcom
> computes point estimates, standard errors, test statistics,
> significance
> levels, and confidence intervals for (possibly) nonlinear
> combinations of
> parameter estimates after any Stata estimation command."
> (see the help file)
> 
> So when Henry feeds -nlcom- his call
>
-nlcom((-.0093/cpi)*((gdpca/cifprice1)-$b*(lagimportca-$a*laglocalca))*8.89)
> -, Stata sees variable names instead of parameter
> estimates, and the error
> message makes the problem abundantly clear. Let me
> replicate:
> 
> **
> sysuse auto, clear
> reg price weight length
> nlcom (myratio: weight/length )
> **
> 
> His second -nlcom- call is:
> -nlcom((-.0093/35)*((36/.33)-$b*(3.7-$a*14.4))*8.89)- which
> Stata evaluates
> to -nlcom
>
((-.0093/35)*((36/.33)-.6892200041267298*(3.7-.1785226557738297*14.4))*8.89)
> -. This, of course, does not contain a reference to a
> parameter estimate,
> either, so Stata returns a scalar, and no other values.
> Where is a standard
> error supposed to come from for a _scalar_? 
> 
> All of which makes me think that Henry really wants
> something else, and my
> money is on -predictnl-.
> 
> 
> HTH
> Martin
> 
> -----Original Message-----
> From: HENRY AKAEZE [mailto:akaezehenry@yahoo.com]
> 
> Sent: Montag, 7. Juni 2010 20:46
> To: martin.weiss1@gmx.de
> Subject: Elasticity using nlcom
> 
> Dear Martin,
> 
> I am doing estimation using the AIDS model. In order to
> estimate elasticity,
> I used nlcom command on an elasticity function I derived
> through
> differentiation as follows:
> 
>
nlcom((-.0093/cpi)*((gdpca/cifprice1)-$b*(lagimportca-$a*laglocalca))*8.89)
> 
> The exogenous variables are CPI, CIF and the lags of import
> and domestic
> products.
> 
> However, stata complained that reference was made to X
> rather
> than _b[X] as follows:
> 
> 
> 
>
expression((-.0093/cpi)*((gdpca/cifprice1)-.6892200041267298*(lagimportca-.1
> 785226557738297*laglocalca))*8.89)
> contains  reference to X rather than _b[X]
> 
> When evaluated at their means I got a value but without
> standard errors and
> p-value as below:
> 
>   nlcom((-.0093/35)*((36/.33)-$b*(3.7-$a*14.4))*8.89)
> 
>  
>
_nl_1:(-.0093/35)*((36/.33)-.6892200041267298*(3.7-.1785226557738297*14.4))*
> 8.89
> 
> 
> 
>
----------------------------------------------------------------------------
> --
> 
>     importca
> |             
> P>|t|      Coef.     
>                
>         [95% Conf. Interval]
>                
>        Std. Err.   
>   t
>
-------------+--------------------------------------------------------------
> --
> _nl_1 -.255856          . 
>             .   
>            
>    .     
>                
>      
> 
>
----------------------------------------------------------------------------
> --
> 
> I need to know what is going on and what I must do to get
> values for the
> standard errors,  t-stat and conf. interval.
> 
> Thank you,
> 
> Henry
> 
> 
>       
> 
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