Date:         Sun, 2 May 2004 23:55:21 -0400
Reply-To:     Doug Fuller <dfuller@WAYNE.EDU>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Doug Fuller <dfuller@WAYNE.EDU>
Subject:      Re: Identifying data combinations
Comments: To: Frank Milthorpe <Frank.Milthorpe@dipnr.nsw.gov.au>
Content-Type: text/plain; charset=us-ascii

>>There are 2**15, or 32,768, possible combinations of
>>presence and absence of 15 symptoms. That's a LONG list of
>>frequencies to make sense of. Unless only a small fraction
>>actually occur, and you have a number of cases that's a
>>significant multiple of the number that do occur, you're
>>going to have a terrible time making sense of the result.
>
>In determining all of these possible combinations it is
>worthwhile to remember that the number of symptoms will
>vary from 0 to all 15. This adds to the complexity of the
>analysis.
>There is no need to use the aggregate function. You can
>create a single variable for each respondent (this can be
>either a string or a numeric variable). Suppose there were
>only three possible symptoms. The full list of possible
>combinations is:
[omitted]
>The above can be create using either a numeric function, eg
>combo = sympt1*100 + sympt2*10 + sympt3, or in a similar
>manner using a string function. I can't remember what the
>limit is for the maximum integer value is in SPSS, but
>2**15 could be close.  Once you have created this variable,
>just do a frequency on the combo variable. Creating the
>data in this form is relatively easy. It is what you do
>with it once you have created it and how you analyse it
>that is potentially much more difficult.

From spssbase.pdf (v9), the Fx.y format can handle up to 40
digits or 39 digits with decimals.

If space is a concern, you can certainly use smaller bases;
i.e. sympt1*4 + sympt2*2 + sympt3, for the above example
using base 2 representation.

Of course, individual symptom retrieval is incredibly
difficult visually, and takes a few lines of syntax
computationally.  But either solution will uniquely encode
the 15 symptom configuration.
--
Doug Fuller
dfuller@wayne.edu
Research Technician, Wayne State University
Department of Psychiatry and Behavioral Neurosciences