Your company has asked you to estimate the proportion of people who prefer the color red over other primary colors for manufacturing purposes. If they want the estimate to be within of the true proportion with confidence, how many people should you survey?
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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An economist is evaluating how frequently the U.S. inflation rate exceeds the Federal Reserve's long-term target of 2% per per month. The economist finds that in 34 of the 48 sampled months, the monthly inflation rate did exceed .
Make a confidence interval for the true proportion of months in which the inflation rate exceeds the target.
We are ___ confident that the inflation rate exceeds the target in between (––––,––––) of months.
A
We are confident that the inflation rate exceeds the target in between of months.
B
We are 95% confident that the inflation rate exceeds the target in between of months.
C
We are 95% confident that the inflation rate exceeds the target in between of months.
D
We are confident that the inflation rate exceeds the target in between of months.

1
Step 1: Identify the sample proportion (p̂) by dividing the number of months where the inflation rate exceeded the target (34) by the total number of sampled months (48). The formula is p̂ = x / n, where x is the number of successes and n is the sample size.
Step 2: Calculate the standard error (SE) for the sample proportion using the formula SE = sqrt((p̂ * (1 - p̂)) / n), where p̂ is the sample proportion and n is the sample size.
Step 3: Determine the z-value for a 95% confidence level. For a 95% confidence interval, the z-value is approximately 1.96 (this value corresponds to the critical value for a two-tailed test).
Step 4: Calculate the margin of error (ME) using the formula ME = z * SE, where z is the z-value for the desired confidence level and SE is the standard error.
Step 5: Construct the confidence interval by adding and subtracting the margin of error from the sample proportion. The confidence interval is given by (p̂ - ME, p̂ + ME).
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