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If am doing some market research and want to answer the question "What percentage of the users of a service, searched for the given service online?". Lets say I go out and get people to take a survey.

How do I calculate the required sample size that would create the correct distribution for a given country or region?

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You might want to ask at – Joel Reyes Noche Mar 9 '13 at 0:23

If we define population as the group of all users of the service, then you want to estimate the proportion of population which searched for the service online. The required sample size can be determined based on

  • confidence level
  • desired size of confidence interval

The determination of sample size is discussed on Wikipedia, a worked out example is given here and probably in every statistics textbook.

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