I'm help a friend who's working in analysis
of business data. The data was acquired from a questionnaire.
Each question has a set of answers and the the user marks
one of that. Futhermore, the answers are made in some way
that the second involves the first, third involves the
second, and so on.
I wold like to know if is correct treat this data
how mutually exclusive. If it's incorrect could any one
gimme some suggestion.
It is impossible to answer this question in the abstract. The answer
really depends on what your friend's objectives are. For many
questions, he may be interested in conditional or marginal rates for
which the dependency just doesn't matter. In other cases, you can
treat it like missing data. Often, ignoring the dependency is not a
problem; usually, you just over/under estamate the variance; only if
the question you are asking the data is very complex is it likely to
make a big difference. Another approach is to test to see if the
dependency is ignorable (often is) and then proceed with the
appropriate marginal analysis.
There is an extensive literature dealing with such items in the
Statistical Sampling/Survey world. Often a local university with have
a stat clinic run by graduate students which can help people with such
problems for free or at a reduced rate. This is probably a good
source of help. (Hopefully your friend has asked questions which
contain the answer he is looking for.)
--Russell Almond
Educational Testing Service
Research Statistics Group, 15-T
Princeton, NJ 08541
Phone: 609-734-1557 FAX: 609-734-5420
Email: --almond@acm.org, --ralmond@ets.org
http://www.stat.washington.edu/bayes/almond/almond.html
[Remove -- from email addresses]
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