A social worker at a large high school wants to estimate the number of days students are absent. He randomly selects 45 students and records the number of days each one is absent. The social worker constructs a 95 percent confidence interval for the true mean number of days students at this school are absent. Which of the following would decrease the margin of error?

A confidence interval’s margin of error decreases when the confidence level is lowered, because a smaller critical value is needed. Changing from 95% to 90% confidence therefore decreases the margin of error. A 99% confidence level would increase it, and using samples of 40 or 30 instead of 45 would also increase it by reducing the sample size.

AI-written and checked against the verified answer.