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Topic: Application question about categorical data and confidence intervals.
Replies: 2   Last Post: Jun 21, 1996 12:04 PM

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Posts: 1
Registered: 12/18/04
Application question about categorical data and confidence intervals.
Posted: Jun 20, 1996 11:53 AM
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I apologize if this question is inappropriate to this group, but I have
not been able to find a better option. I am presently surveying a market
that has 570 firms to determine which providers they use for particular
services. The goal is to construct a breakdown of the marketshare that
each service provider holds within the 570 firms. So far we have spoken to
about 60% of the firms and have achieved results to the effect of:
Brand A: 30%
Brand B: 25%
Brand C: 20%
All others: 25%

My question is: How many firms do we have to survey before we can say that
our results represent the service usage of the entire market of 570 firms
within a particular range of error? And how do I determine what my margin
of error is at a given sample size?

Any help would be greatly appreciated!
Please e-mail me at

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