MOE ≈ z·√(p(1−p)/n) with conservative p=0.5.
For a proportion with conservative p = 0.5, margin of error ≈ z × √(p(1−p)/n) with sample size n ≥ 1 and z from common confidence levels 90% / 95% / 99% (normal approximation). Not a substitute for survey design software.
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