1. CONFIDENCE INTERVALS FOR PROPORTIONS Mrs. Watkins Chapter 19 AP Statistics

2. EX: A survey of 650 people is taken which indicates that 45% of American citizens are in favor of a tax cut for teenage workers.

3. What is the true proportion of people who favor this tax cut? Use a z proportion confidence interval to estimate the true proportion:

5. Z or T? All proportion intervals are Z intervals

6. Common Confidence Levels 90% CI…critical value = ? 95% CI…critical value = ? 99% CI…critical value = ?

7. ASSUMPTIONS/CONDITIONS 1.Large enough sample to assume a relatively normal distribution np > 10 nq >10 2.Simple Random Sample

8. Interpretation Sentence “I am 95% confidence that the true population proportion of people who favor the tax cut for teenage workers is between_____ and ______.” Fill in the red underlined portion with correct context.

9. Ex: A survey of 200 recent fatal traffic accidents in a certain state showed that 86 were alcohol related. Find the 90% confidence interval of the true proportion of fatal traffic accidents which are alcohol related.