Question

A study showed that 15 of 30 cell phone users with a headset missed their exit, compared with 3 of 30 talking to a passenger. Construct a 90 percent confidence interval for the difference in proportions. (Round your answers to 4 decimal places. A negative value should be indicated by a minus sign.) The 90 percent confidence interval is from ___ to ___ .

Answer 1

x1                =	15	x2                =	3
p̂1=x1/n1 =	0.5000	p̂2=x2/n2 =	0.1000
n1                       =	30	n2                       =	30
estimated difference in proportion   =p̂1-p̂2   =			0.4000
std error Se =√(p̂1*(1-p̂1)/n1+p̂2*(1-p̂2)/n2) =			0.1065
for 90 % CI value of z=		1.645
margin of error E=z*std error =		0.1751
lower bound=(p̂1-p̂2)-E=		0.2249
Upper bound=(p̂1-p̂2)+E=		0.5751
from above 90% confidence interval for difference in population proportion =(0.2249 to 0.5751)