1. All other things the same, a 90% confidence interval is shorter than a 95% confidence interval.
2. Ninety-five percent z-intervals have the form of a statistic plus or minus 3 standard errors of the statistic.
3. By increasing the sample size from n = 100 to n = 400, we can reduce the margin of error by 50%.
4. If we double the sample size from n = 50 to n = 100, the length of the confidence interval is reduced by half.
5. If the 95% confidence interval for the average purchase of customers at a department store is $50 to $110, then $100 is a plausible value for the population mean at this level of confidence.