A survey of 144 retail stores revealed that the average price of a DVD was $375 with a standard error of $20. If 95% and 98% confidence intervals were developed to estimate the true cost of the DVD, what differences would they have?
A) Standard errors
B) Interval widths
C) Z-values would be the same
D) Both "b" and "c"
E) None of the choices are correct

Question

Quizplus · Accepted Answer

The 95% confidence interval would be narrower than the 98% confidence interval because the 95% confidence interval has a lower level of confidence, which means that it is less likely to include the true population mean. The standard errors would be the same for both confidence intervals because the standard error is a measure of the variability of the sample mean, which is not affected by the level of confidence. The z-values would be different for the two confidence intervals because the z-value is used to determine the critical value for the confidence interval, and the critical value is different for different levels of confidence.

A Survey of 144 Retail Stores Revealed That the Average