Question 418462
A research team would like to estimate the proportion of children (aged 6 to 12) that currently exhibit a deficiency in this micro-nutrient. 
For their purposes a 90% CI must be no wider than 9.5% to be useful. Given these constraints, the number of children required for the sample is?
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2*E = 0.095
E = 0.0475
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E = zs/sqrt(n)
0.0475 = 1.645*s/sqrt(n)
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n >= [1.645s/0.0475]^2
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I believe you need a value of the standard deviation (s).
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Cheers,
Stan H.