 
Summary: Math 140
Introductory Statistics
Professor Bernardo Ábrego
Lecture 26
Sections 8.3
8.3 A Confidence Interval for the
Difference of two Proportions
A very common and important situation
involves taking two samples independently
from two different populations with the goal of
estimating the size of the difference between
the proportion of successes in one population
and the proportion of successes in the other.
Example
A recent poll of 29,700 U.S. households
found that 63% owned a pet. The percentage
in 1994 was 56%. [Source: American Pet Products
Manufacturers Association, www.appma.org.]
The two populations are the households in
the United States in 1994 and the households
