Over the first days of the semester, one student is late to class on days. Construct a confidence interval for the true proportion of time this student is late.
Table of contents
- 1. Introduction to Statistics53m
- 2. Describing Data with Tables and Graphs2h 1m
- 3. Describing Data Numerically1h 48m
- 4. Probability2h 26m
- 5. Binomial Distribution & Discrete Random Variables2h 55m
- 6. Normal Distribution & Continuous Random Variables1h 48m
- 7. Sampling Distributions & Confidence Intervals: Mean2h 8m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 20m
- 9. Hypothesis Testing for One Sample2h 23m
- 10. Hypothesis Testing for Two Samples3h 25m
- 11. Correlation1h 6m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 30m
- 14. ANOVA1h 4m
8. Sampling Distributions & Confidence Intervals: Proportion
Confidence Intervals for Population Proportion
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You want to make a 97% confidence interval for the population proportion of people between 20−30 years old who have gotten a speeding ticket in the past 2 years. A prior study found that 26% of people between 20−30 years old have received a speeding ticket in the last year. If you want your estimate to be accurate within 3% of the true population proportion, what is the minimum sample size needed?
A
1007
B
1006
C
579
D
1309

1
Identify the key components needed for calculating the sample size for a confidence interval: the desired confidence level, the margin of error, and the estimated proportion from a prior study.
The formula for calculating the sample size for a proportion is: , where is the z-score corresponding to the confidence level, is the estimated proportion, and is the margin of error.
For a 97% confidence level, find the z-score. This can be done using a standard normal distribution table or calculator. The z-score for 97% confidence is approximately 2.17.
Substitute the values into the formula: = 0.26 (from the prior study), = 0.03 (desired margin of error), and = 2.17.
Calculate the sample size using the formula: . This will give you the minimum sample size needed.
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