Posted by John on Monday, November 5, 2012 at 9:53am.
A random sample of 250 men yielded 175 who said they'd ridden a motorcycle at some time in their lives, while a similar sample of 215 women yielded only 43 that had done so. Find a 99% confidence interval for the difference between the proportions of men and women who have ridden motorcycles.
.4688 ± .085
.5 ± .112
.5 ± .103
.5 ± .085
.5 ± .078

Statistics  MathGuru, Monday, November 5, 2012 at 6:57pm
Let's look at your data:
n1 = 250
n2 = 215
p1 = 175/250
p2 = 43/215
Formula:
CI99 = (p1  p2) ± 2.58 √(p1(1p1)/n1 + p2(1p2)/n2)
Substitute the values into the formula and calculate. (Convert all fractions to decimals.)
You should be able to select your answer once you have determined the interval.

Statistics  Math Whizz, Thursday, March 14, 2013 at 5:04pm
.5 ± .103

Statistics  Math Whizz, Thursday, March 14, 2013 at 5:05pm
.5 } .103, because, as the math guru said the formula is (p1  p2) } 2.58 ã(p1(1p1)/n1 + p2(1p2)/n2), the 2.58 comes from the zscore table. The question doesn't want you to solve the whole formula, just the first and last.. (175/250)(43/215)=.5 and the ã(p1(1p1)/n1 + p2(1p2)/n2=.1026887336
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