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Re: Samples between PSPP and SPSS
From: |
Andy Choens |
Subject: |
Re: Samples between PSPP and SPSS |
Date: |
Wed, 21 Sep 2011 15:03:11 -0400 |
User-agent: |
KMail/4.7.1 (Linux/3.0.0-11-generic; KDE/4.7.1; x86_64; ; ) |
Jason, John,
Thanks for the information. I am writing most of my syntax on PSPP on my Linux
box but I will check it against a copy of SPSS
I have access to periodically. Reproducability of the sample selection is
important and I will see if I can get the same results
from both SPSS and PSPP when I use the same seed across both systems.
I am also going to see if I can reproduce the same sample outcome using R.
Should make for an interesting experiment. The only copy of SPSS that I have
regular access to is Version 11, which may or
may not make a difference. If I can get my hands on a newer copy of SPSS, I'll
test it there too.
Thanks
--andy
On Wednesday, September 21, 2011 06:29:01 PM John Darrington wrote:
> In SPSS, you can choose between the MC rng and the Mersenne Twister
> using the commands:
>
> SET RNG=MC.
>
> or
>
> SET RNG=MT.
>
>
> See the SPSS documentation for details.
>
>
> PSPP doesn't implement this. (Perhaps we should?) Like Jason says, we
> always use the
> Mersenne Twister.
>
> I also notice that the SPSS docs say that the default seed is 2000000 whereas
> we set it
> from the realtime clock.
>
> I'd be interested to see some of your experiements to see what is necessary
> to make them
> match (if it's at all possible). It would also be interesting to see how the
> random
> number distributions fare when analysed with some of the non-parametric tests.
>
> J'
>
>
>
> On Wed, Sep 21, 2011 at 12:50:47PM -0400, Jason Stover wrote:
> On Wed, Sep 21, 2011 at 10:12:39AM -0400, Andy Choens wrote:
> > If I set a set to a consitent value, say 123, and create a sample in
> PSPP will it match the sample created by SPSS?
>
> I doubt it, but can't be sure becaus the source code to SPSS is kept
> secret.
>
> > If someone
> > knows which pseudo number generator is being used by PSPP and SPSS
> respectively that would also be a big help so I
could
> > replicate / confirm output indpenedently.
>
> As of about 10 years ago, most of SPSS used a multiplicative
> congruential random number generator. It had a period of either 2^31 -
> 1 or 2^32 - 1. They may still use such a generator, since changing it
> would cause users' old syntax to give different answers.
>
> PSPP uses the Mersenne Twister, which has a period of 2^19937 - 1, as
> implemented in GSL. You can see the code for it in src/math/random.c.
>
> -Jason
>
> _______________________________________________
> Pspp-users mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/pspp-users
>
>
- Samples between PSPP and SPSS, Andy Choens, 2011/09/21
- Re: Samples between PSPP and SPSS, Jason Stover, 2011/09/21
- Re: Samples between PSPP and SPSS, John Darrington, 2011/09/21
- Re: Samples between PSPP and SPSS, Andy Choens, 2011/09/21
- Re: Samples between PSPP and SPSS, Ben Pfaff, 2011/09/21
- Re: Samples between PSPP and SPSS, Andy Choens, 2011/09/21
- Re: Samples between PSPP and SPSS, Ben Pfaff, 2011/09/21
- Re: Samples between PSPP and SPSS, Andy Choens, 2011/09/22
- Re: Samples between PSPP and SPSS, Karel Novotny, 2011/09/22