On 10/26/07, Frank Thomas <[EMAIL PROTECTED]> wrote: ... > BTW: Contrary to some ideas both R & SPSS can be programmed and the > algorithms for both have been published. So, no matter whether open > source or private property you know what you do (if you want).
This is off the point of Matt's original question and I apologize for hijacking the thread but where have the algorithms that underly the SPSS procedures been published? My particular interest is in the methods for the linear mixed models implemented in MIXED in SPSS (and also PROC MIXED in SAS). A person who was quite enthusiastic about the MIXED procedure in SPSS sent me a PDF file about MIXED that I suppose could be considered a description of the algorithms as long as you didn't read it too closely. However, the descriptions are far too vague to use them as a basis for writing code and furthermore they jump back and forth between two or three different representations of the model without tying the different threads together. There is no indication of what representation forms the basis of the code and how the calculations are implemented. Even more alarming, parts of it are flat-out wrong. Even the mixed-model equations as given in this document are wrong, as one would quickly find out if one tried to implement them. The organization is disjointed and generally the language and grammar indicate that it has not been copy edited carefully. I would not give it a good grade if it were submitted as a project report in my statistical computing course. I have been unable to trace the source of this document. It is definitely a discussion of the computational algorithms in MIXED but I haven't been able to track its original source. In a way I hope it was a preliminary draft or something like that. If SPSS released this version as an official publication it is a sign that they have fallen on hard times. If one simply needs to have a reference to cite regarding the calculations done n your analysis then a document like this, suitably corrected, might do. I don't know if this is what you meant by saying that the algorithms have been published but if it is then this is not sufficient for the purposes of investigating the computational methods. A few years ago Brian Ripley mentioned in a presentation, I believe to the Royal Statistical Society, the need for a reference implementation of a statistical computing technique. That is, one should provide code that is accessible to, usable by and modifyable by other researchers in the field. (Brian: If you know the presentation to which I am referring, can you provide a reference or URL please?) Perhaps not for students who simply need to apply a few statistical techniques but certainly for researchers in the statistical techniques and computational methods there is a world of difference between a closed-source implementation with a supplementary document describing the alleged computation method and an open-source implementation. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
