Question: how to calculate standard deviation with proportion?
Answer: For a proportion, the appropriate standard deviation is √pqn p q n . However, in the error bound formula, we use √p′q′n p ′ q ′ n as the standard deviation, instead of √pqn p q n . In the error bound formula, the sample proportions p′ and q′ are estimates of the unknown population proportions p and q.