In: Statistics and Probability
On September 1, 1939, Germany invaded Poland, causing Britain and France to declare war on Germany. Between September 1 and September 6 that year, Gallup conducted a poll asking whether the U.S. should send its Army and Navy abroad to fight against Germany. 84% of 926 Americans surveyed said no.
(a) Construct a 95% confidence interval for the proportion of Americans who didn’t believe that the U.S. should send its Army and Navy abroad to fight against Germany.
(b) Construct a one-side 95% confidence interval with an upper bound for the proportion of Americans who didn’t believe that the U.S. should send its Army and Navy abroad to fight against Germany.
a)
95% CI is
- Z/2 * sqrt [ ( 1 - ) / n ] < p < + Z/2 * sqrt [ ( 1 - ) / n ]
0.84 - 1.96 * sqrt [ 0.84 ( 1 - 0.84) / 926 ] < p < 0.84 + 1.96 * sqrt [ 0.84 ( 1 - 0.84) / 926 ]
0.816 < p < 0.864
95% CI is ( 0.816 , 0.864 )
b)
95% Upper bound is
+ Z * sqrt [ ( 1 - ) / n ] > p
0.84 + 1.645 * sqrt [ 0.84 ( 1 - 0.84) / 926 ] > p
0.860 > P