11/17/09
Lecture 19
1
STOR 155 Introductory Statistics
Lecture 19: Comparing two proportions
Section 8.2
The
UNIVERSITY
of
NORTH CAROLINA
at
CHAPEL HILL

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11/17/09
Lecture 19
2
Two populations: an extension of Lecture 18
•
Population 1: with proportion
•
Population 2: with proportion
•
Interested in the
difference
•
Sample 1:
size
count
proportion
•
Sample 2:
size
count
proportion
•
Consider the
difference
•
Assume the two samples are
independent
, and both
and
are
large
.
p
1
p
2
p
1
à
p
2
D
=
p
ê
1
à
p
ê
2
p
ê
1
=
X
1
=n
1
p
ê
2
=
X
2
=n
2
n
1
X
1
n
2
X
2
n
1
n
2