1. 6.3 Confidence Intervals for Population Proportions
The fun continues…

2. Point Estimate for the Population Proportion p
Remember p from a binomial experiment is the probability of success? This is also called the population proportion.
p = x x = number of successes
n n = total # in sample
p = point estimate for
population proportion

3. Example 1
In a survey of 3859 adults from the U.S., 1177 said that of all the presidents from the 20th century, Franklin D. Roosevelt was the greatest. Fins a point estimate for the population proportion of adults who agree.

4. Confidence Intervals for a Population Proportion p

5. Steps to construct the interval
Identify n and x
Find the point estimate
Verify you can approximate to the normal distribution
Find the critical value zc
Find the margin of error
Find the endpoints

6. Example 2
Use the data from example 1 to construct a 90% confidence interval for the proportion of adults who say Roosevelt was the greatest president of the 20th century.
Recall, x= 1177 and n = 3859
INTERPRET your results!

7. Example 3 (with calculator)
From a survey of 900 adults, construct a 99% confidence interval for the proportion of adults who think that people over 75 are the most dangerous drivers. (33% according to graph)
STAT – Tests A:1-PropZInt
x = .33 x 900
n = 900

8. III. Increasing Sample Size to Increase Precision

9. Example 4
You wish to estimate, with 90% confidence and within 2% of the true population, the proportion of adults age who have high blood pressure. Find the minimum sample size needed if (1) no preliminary estimate is available and (2) a previous survey found that 4% of adults in this age group had high blood pressure.

10. Classwork/Homework Together p308 #3, 13, 25 Classwork p308 #4, 14, 26
Homework p308 #6-12 even, 27
Together p308 #3, 13, 21, 25
Classwork p308 #4, 14, 22, 26
Homework p308 #6-12 even, 24, 27