Yes I was wrong, the mean ttest example makes it very clear. thanks a lot
-------- Original-Nachricht --------
> Datum: Mon, 24 Nov 2008 15:15:42 +0100
> Von: "Martin Weiss" <[email protected]>
> An: [email protected]
> Betreff: RE: st: RE: significance of mean and median
> Line for the server...
>
> You probably wanted to say that "the CI did not overlap zero". Regarding
> the
> proper interpretation of statistical tests, you should consult any
> undergraduate statistics textbook. The 5% level means that your rejection
> of
> H0 will be wrong in 5% of the times you conduct this test. Note the
> parallels between -mean- and -ttest-
>
> *******
> sysuse auto, clear
> replace mpg=mpg-20
> ttest mpg=0
> mean mpg
> ******
>
> -ttest- output also gives you one-sided tests. Your question regarding
> whether you can conclude that the mean is negative is answered by the
> leftmost output of -ttest-.
>
> Regarding your -signtest-, do not try to reinvent the wheel. Stata
> provides
> a whole submenu of regression diagnostics which can be employed to
> discriminate between two competing models...
>
>
> HTH
> Martin
>
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Bastian
> Steingros
> Sent: Monday, November 24, 2008 3:02 PM
> To: [email protected]
> Subject: Re: st: RE: significance of mean and median
>
> Hi Martin,
>
> Using *mean* for several variables, stata has provided result like
> mean_var_x=-0.056 and the upper end of the CI did not overlap zero. Given
> a
> 95% CI, does the result indicate that the mean of var_x
> is negative at the 5% level (1% when used a 99% CI)?
>
> Is signtest not appropriate to compare the median inaccuracies of model 1
> +2
> or more generally to the medians of two variables?
>
> b
>
>
>
> -------- Original-Nachricht --------
> > Datum: Mon, 24 Nov 2008 13:46:42 +0100
> > Von: "Martin Weiss" <[email protected]>
> > An: [email protected]
> > Betreff: st: RE: significance of mean and median
>
> >
> > Line for the server...
> >
> > On the second part, without judging the appropriateness of your
> procedure,
> > "(GDP_predicted - GDP)" looks like a straightforward residual to me,
> > available from -predict-, which would generate a new variable, ready to
> be
> > divided by "GDP" with -replace-. Afterwards -ttest- compares means and
> > -median- compares medians...
> >
> > HTH
> > Martin
> >
> >
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]] On Behalf Of Bastian
> > Steingros
> > Sent: Monday, November 24, 2008 12:56 PM
> > To: [email protected]
> > Subject: st: significance of mean and median
> >
> > Hello everybody,
> >
> > I have this problem:
> >
> > After creating the descriptive statistics of my sample I want to show
> that
> > the mean of a certain variable is statistically significant.
> > For example the mean of var1 is 0,45. Now I want to show that the
> positive
> > sign is significant.
> > Is ttest the appropriate way to do so?
> >
> > Moreover, in another sample I want to predict the GDP using two
> different
> > regression models.
> > Finally, I want to compare the predicted values with the real GDP, that
> > is,
> > I will compare the mean and the median of the inaccuracy.
> > Inaccuracy is defined as (GDP_predicted - GDP)/GDP
> >
> > Is there a way to show that the median (mean) inaccuracies of the two
> > models
> > are statistically different from each other?
> >
> > may be *signtest*???
> >
> > thanks
> >
> > bastian s
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