Dear Statalist,
I must say that i only just now saw dr. williams response to my generating a
data set query just this moment, and only AFTER having sent a thank you to
the three previous graciously replying guys...so a special thank you to dr.
williams for his very helpful reply and guidance.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Richard Williams
Sent: Thursday, August 19, 2004 11:14 AM
To: [email protected]
Subject: Re: st: RE: generating data sets with specific parameters
At 06:56 PM 8/18/2004 -0500, Scott Merryman wrote:
>You might try -corr2data-
-corr2data- is good if you want the parameters to come out EXACTLY as
specified, e.g. if you say the mean is 10 and the SD is 2 then that is what
they will indeed be in the data set that is created. It is like creating a
population with the specified parameters. -drawnorm-, on the other, draws
a random sample from a population with the specified parameters; hence,
because of sampling variability, the numbers in the sample will differ a
bit from the numbers you specify.
-corr2data- is especially good if, say, you have a published correlation
matrix and want to replicate the results. In SPSS, you would typically
just input the means, correlations and SDs; in Stata you create a fake data
set. -drawnorm- is probably better if you are doing some sort of
simulation.
Note that -corr2data- always produces the exact same data set unless you
use the -seed- parameter of -corr2data- (not the separate -seed- command.)
Key caution: If your goal is to use -corr2data- to analyze a published
correlation matrix, remember, these are simulated data, not the
original. There is only so much you can do, e.g. you can't go computing
interaction terms, take logs, analyze a subsample, or anything like
that. You can do stuff like run OLS regressions using different subsets of
the variables. The ONLINE help for -corr2data- goes over this a bit.
I discuss the use of -corr2data- on pages 7-9 of
http://www.nd.edu/~rwilliam/stats1/OLS-Stata.pdf
-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
FAX: (574)288-4373
HOME: (574)289-5227
EMAIL: [email protected]
WWW (personal): http://www.nd.edu/~rwilliam
WWW (department): http://www.nd.edu/~soc
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