Question: how to calculate confidence interval for two proportions?
Answer: Compute alpha (α): α = 1 - (confidence level / 100) α = 1 - (90/100) = 0.10. Find the critical probability (p*): p* = 1 - α/2 = 1 - 0.10/2 = 0.95. The critical value is the z-score having a cumulative probability equal to 0.95. From the Normal Distribution Calculator, we find that the critical value is 1.645.