In a group of 100 people, the average GFR is 85 ml/ min with a standard detion of 25. What is the range for 90% confidence interval?
(A) 81-89 (B) 80-90 (C) 75-95 (D) 70-100
(A) Ans: A. 81-89(Ref: Park 24/e p888, 22/e p793; Essentials of Biostatistics 2/e pI70)Range for 90% confidence interval in the given question is 81-89.Confidence intervals:Lower limit & upper limit estimates for statistic given by:Lower Limit: statistic - C x SE (statistic)Upper Limit: statistic + C x SE.Confidence coefficient:C = Confidence coefficient = 1.65 for 90% confidence intervalC= 1.96 for 95% confidence intervalC= 2.58 for 99% confidence intervalC = 3.29 for 99.9% confidence intervalNow for 90% confidence interval:Upper limit = 85 + (1.65 x 2.5) = 85 + 4 = 89.Lower limit = 85 + (1.65 x 2.5) = 85 - 4 = 81.Hence, for 90% confidence interval will 81-89.