Re: st: Simulate and corr2data

[Richard Williams <Richard.A.Williams.5@nd.edu>]

There is a seed option in corr2data, e.g.

corr2data x y, n(2000) corr(C) seed(123)

It isn't in the manual, so I assume it is a relatively recent addition; it 
shows up in help.  If you change the seed, you get a different data set.

Keep in mind that even though you can get different data sets, the means, 
correlations and standard deviations will always be exactly as specified in 
corr2data, i.e. there won't be any sampling variability that will cause 
sample values to differ somewhat from the values you have specified.  I'm 
not sure what you are trying to do, but if your goal was to draw a random 
sample from a population with given parameters, corr2data doesn't do that, 
i.e. it may be too good for what you have in mind.

At 09:48 PM 1/20/2004 +0000, Allan Reese wrote:

> Followed example for simulate except to use corr2data rather than gen to
> create the dataset.  Imagine my chagrin when each repetition gave the same
> answer!  So tried corr2data from the command prompt and found it gives the
> same sample time after time, regardless of any setting of seed.  Does
> anyone have a fix please?  Is this an unintended bug?  Looks counter
> intuitive and ought to happen only if "set seed" used to restart the
> sequence.
>
> If corr2data can not produce independent samples, can I have comments
> please on whather it is equivalent to use bootstrap with a large N and
> relatively small sample size.  I am interested in sample statistics that
> depend on the overall distribution of points, and the default use of
> bootstrap to select multiple samples of size N from N points must rely
> upon random points being used once, twice or more - or have I completely
> misunderstood?
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/