The following MINITAB output presents a confidence interval for a population mean.
$\begin{array}{crrrcc}
\hline \text { Variable } & \mathrm{N} & \text { Mean } & \text { StDev } & \text { SE Mean } & 99 \% \text { CI } \
\mathrm{x} & 29 & 114.9872 & 22.1061 & 4.1050 & (103.645,126.329) \
\hline
\end{array}$
Use the information in the output to construct a $98 \%$ confidence interval.
A) $( 112.575,117.400 )$
B) $( 104.860,125.114 )$
C) $( 112.833,117.141 )$
D) $( 103.645,126.329 )$

Question

The following MINITAB output presents a confidence interval for a population mean.
 $\begin{array}{crrrcc}
\hline \text { Variable } & \mathrm{N} & \text { Mean } & \text { StDev } & \text { SE Mean } & 99 \% \text { CI } \
\mathrm{x} & 29 & 114.9872 & 22.1061 & 4.1050 & (103.645,126.329) \
\hline
\end{array}$
Use the information in the output to construct a $98 \%$ confidence interval.
A) $( 112.575,117.400 )$
B) $( 104.860,125.114 )$
C) $( 112.833,117.141 )$
D) $( 103.645,126.329 )$

Quizplus · Accepted Answer

The confidence interval width changes with the confidence level. A 98% confidence interval will be narrower than a 99% confidence interval but wider than a 95% confidence interval, given the same sample statistics. Since option D represents the 99% confidence interval, and options A and C are narrower than option D, option B is the only plausible choice for a 98% confidence interval, being narrower than the 99% interval but wider than what would be expected for a 95% interval.

The Following MINITAB Output Presents a Confidence Interval for a Population