Re: Samples between PSPP and SPSS

[Jason Stover]

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