st: RE: stata command for joint significant in large sample test

["Schaffer, Mark E" <M.E.Schaffer@hw.ac.uk>]

Joanne,

> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu 
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of 
> Joanne Marshall
> Sent: 21 January 2007 02:59
> To: statalist@hsphsun2.harvard.edu
> Subject: st: stata command for joint significant in large sample test
> 
> Dear fellow,
> 
> if i was to test the joint significance test using a large 
> sample test in stata for educ, wage and married
> 
> which of the following command do I use in Stata?
> 
> test educ wage married
> 
> or
> 
> test educ+wage+married=0

The former.  Why?  Hint: look at the output of the -test- command.
Stata will list the components of the hypothesis being tested.

In the first case, there are 3 components to the hypothesis, namely that
the coeffs on each of the 3 variables equal zero.  This makes sense.
It's just like an F test for the significance of a regression.

In the second case, there is 1 component to the hypothesis, namely that
the 3 coeffs added together equal zero.  This doesn't make sense in your
context (and wouldn't in most others, either).

Cheers,
Mark

NB: Yes, I know this looks like a homework question and would normally
be unsuitable list material, but I figured that this could be spun into
a "teaching Stata" answer.

> they generate different results, actually opposite results, 
> one being significant and one insignificant. Note I will want 
> to use a large sample test here.
> 
> Thank you very much, any comments are appreciated!
> 
> Cheers
> Jo
> 
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