Date:         Thu, 4 Oct 2007 13:20:12 -0300
Reply-To:     Hector Maletta <hmaletta@fibertel.com.ar>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Hector Maletta <hmaletta@fibertel.com.ar>
Subject:      Re: calculating an index
Comments: To: Dirk Sebastian Friedrich <DFriedrich@barc.de>
In-Reply-To:  <E72F29F51E19C04AB82262988638509A8A80DF@barc-server.barc-intranet.de>
Content-Type: text/plain; charset="us-ascii"

         Dirk,
         I do not really see your difficulty. If you simply want to add the
score over the five questions, each with a 7-point scale ranging from 7 to 1
in a reverse scale (7 is low and 1 is high), your index might be the sum or
the average of the five questions, period. Examples:

         COMPUTE
INDEX=SUM(QUESTION1,QUESTION2,QUESTION3,QUESTION4,QUESTION5).
         COMPUTE
INDEX=MEAN(QUESTION1,QUESTION2,QUESTION3,QUESTION4,QUESTION5).

         I'd recommend the MEAN function, just in case somebody omitted
responding some of the five questions. Also, you may specify (as an argument
to the MEAN function) the minimum number of non-missing questions required
to compute the mean, writing for instance MEAN.3 if you require at least
three valid responses for the index to be computed validly.

         Now, this kind of index is a very simple one, giving the same
weight to each of the five questions. You might use a more sophisticated
approach such as CATPCA (with input variables defined as ordinal) which is
included in the SPSS CATEGORIES module, to generate a principal component
analysis for categorical variables, and using the score of the main
component as an index. Note that the simple index with COMPUTE assumes that
the scores in the questions are interval scales, which may not be right.
Assuming they are interval scales you may also apply classical factor
analysis with the FACTOR command. These commands, CATPCA or FACTOR, give
each of the five questions a different weight, and take their
inter-correlation into account.

         Hector


         -----Original Message-----
From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of
Dirk Sebastian Friedrich
Sent: 04 October 2007 12:11
To: SPSSX-L@LISTSERV.UGA.EDU
Subject: calculating an index

         Dear members,



         I've got a general problem concerning the structure of SPSS .



         What I want to do is calculating an index about the benefit of a
product
         group.



         I've got 5 questions each asking for the benefit of a different
product
         and 7 answer options per question (1=high benefit to 7=low
benefit).



         What I need to do now, is adding up all answers per answer option
of the
         5 products, for being able to calculate the mean (=my benefit-index
of
         all the products).



         That's exactly the step where I am failing. (For the "usual"
SPSS-way
         the column for calculating would be 5 times long as before.)

         I want to be able to research other answers of a survey against the
         background of the index.



         Is there anyone who knows what I can do for calculating the index
in
         SPSS and still being able to conduct further analysis against the
         background of the index.



         Thanks in advance!





         Dirk