MATH 225N Week 6 Assignment: Understanding Confidence Intervals – Excel

MATH 225N Week 6 Assignment: Understanding Confidence Intervals – Excel Calculate a Confidence Interval for a Proportion - Excel Question In a random sample of 350 attendees of a minor league baseball game, 184 said that they bought food from the concession stand. Create a 95% confidence interval for the proportion of fans who bought food from the concession stand. Use Excel to create the confidence interval, rounding to four decimal places. ________________________________________ Yes that's right. Keep it up! ________________________________________ (0.4734, 0.5780) Answer Explanation Correct answers: • 0.4734 • 0.5780 The confidence interval for the unknown population proportion p is (p̂ −z⋆p̂ (1−p̂ )n‾‾‾‾‾‾‾‾‾√,p̂ −z⋆p̂ (1−p̂ )n‾‾‾‾‾‾‾‾‾√). The confidence interval can be calculated using Excel. 1. Identify α. Click on cell A1 and enter =1−0.95 and press ENTER. 2. Thus, α=0.05. Enter the number of successes, x=184, and sample size, n=350, in the Excel sheet in cells A2 and A3. To find the proportion of successes, p̂ , click on cell A4 and enter =A2/A3 and press ENTER. 3. Thus, p̂ ≈0.5257. Use the NORM.S.INV function in Excel to find z⋆. Click on cell A5, enter =NORM.S.INV(1−A1/2), and press ENTER. 4. The answer for z⋆, rounded to two decimal places, is z⋆≈1.96. To calculate the standard error, p̂ (1−p̂ )n‾‾‾‾‾‾‾‾‾√, click on cell A6 and enter =SQRT(A4∗(1−A4)/A3) and press ENTER. 5. The answer for the standard error, rounded to four decimal places, is p̂ (1−p̂ )n‾‾‾‾‾‾‾‾‾√≈0.0267. To calculate the margin of erro