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I have 4 test strata and I need to estimate sample size for each. Each strata have different proportion value (based on historical data):

  • Stratum #1- Proportion = 0.75%
  • Stratum #2- Proportion = 1.5%
  • Stratum #3- Proportion = 5.5%
  • Stratum #4- Proportion = 1.77%

Population proportion= 1.25%

Next I need to calculate sample size using normal approximation to binomial distribution, which proportion value I should use in this case? Using population proportion will produce same sample size for each strata. Using proportion value from each stratum will result in different sample size for each stratum.

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  • $\begingroup$ What are these proportions of? What do you need to estimate? Your question is incomplete as asked. Note that binomial approximations will be awful unless you have samples of a few hundred, so that $np>10$ say. For $n_1 p_1 > 10$ to happen, $n_1 > 10 / 0.0075 = 1333$. $\endgroup$ – StasK Feb 10 '17 at 23:00

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