Confidence Interval Estimator for the Population Proportion

Which of the following values below represents the critical value for a 98% confidence interval?

• 1.645

• 2.054

• 2.326

• 3.091

A 90% confidence interval for the average salary of all CEOs in the electronics industry was constructed using the results of a random survey of 45 CEOs. The interval was (₱1,390,480, ₱1,541,440). Give a practical interpretation of the interval.

• 90% of the sampled CEOs have salaries that fell in the interval ₱1,390,480 to ₱1,541,440

• 90% of all CEOs in the electronics industry have salaries that fall between ₱1,390,480 to ₱1,541,440

• We are 90% confident that the mean salary of the sampled CEOs falls in the interval ₱1,390,480 to ₱1,541,440.

• We are 90% confident that the mean salary of all CEOs in the electronics industry falls in the interval ₱1,390,480 to ₱1,541,440. 

A researcher at a major hospital wishes to estimate the proportion of the adult population of the nation. that has high blood pressure.  How large a sample is needed in order to be 90% confident that the sample proportion will not differ from the true proportion by more than 5%?

• 109

• 164

• 271

• 542

Which of the following actions would produce a confidence interval with a smaller width assuming all other contingencies remained constant?

• Using a higher confidence level

• Using a lower confidence level

Which of the following changes to a study would result in a narrower confidence interval?

• increasing the confidence level, increasing the sample size

• decreasing the confidence level, decreasing the sample size

• increasing the confidence level, decreasing the sample size

• decreasing the confidence level, increasing the sample size.

It was found that in a sample of 90 teenage boys, 70% of them have received speeding tickets. What is the 90% confidence interval of the true proportion of teenage boys who have received speeding tickets?

• (0.621, 0.780)

• (0.591, 0.812)

• (0.584, 0.830)

• (0.615, 0.805)

A recent study of 750 Internet users in the Philippines found that 35% of Internet users were women. What is the 95% confidence interval of the true proportion of women in the Philippines who use the Internet?

• 0.321 < p < 0.379

• 0.316 < p < 0.384

• 0.309 < p < 0.391

• 0.305 < p < 0.395

A sample of 400 scooter motorcycles showed that 80 scooter motorcycles cost over ₱120,000. What is the 99% confidence interval of the true proportion of scooter motorcycles costing over ₱120,000?

• 0.001 < p < 0.005

• 0.566 < p < 0.693

• 0.148 < p < 0.252

• 0.023 < p < 0.045

If 827 represents "no" voters out of 2584, construct a 95% confidence interval for the "no" group.

• [0.300, 0.340]

• [0.298, 0.342]

• [0.302, 0.338]

• [0.288, 0.352]

A preliminary study suggests that 87% of people agree on an issue. How large must your sample size be so you could be within ± 3% of p calculate at 90% confidence?

• 5

• 7

• 338

• 466