The following MINITAB output presents a confidence interval for a population mean. $$\begin{array} { c r r r c c }
\hline \text { Variable } & \mathrm { N } & \text { Mean } & \text { StDev } & \text { SE Mean } & 99 \% \mathrm { CI } \
\mathrm { x } & 67 & 71.0754 & 26.3867 & 3.2236 & ( 62.525,79.626 ) \
\hline
\end{array}$$ How many degrees of freedom are there?
A) 66
B) 3.2236
C) 68
D) 67

Question

The following MINITAB output presents a confidence interval for a population mean. $$\begin{array} { c r r r c c } 
\hline \text { Variable } & \mathrm { N } & \text { Mean } & \text { StDev } & \text { SE Mean } & 99 \% \mathrm { CI } \
\mathrm { x } & 67 & 71.0754 & 26.3867 & 3.2236 & ( 62.525,79.626 ) \
\hline
\end{array}$$ How many degrees of freedom are there?
A) 66
B) 3.2236
C) 68
D) 67

Quizplus · Accepted Answer

The degrees of freedom for a confidence interval for a population mean, when the sample standard deviation is used as an estimate for the population standard deviation, is calculated as $n - 1$, where $n$ is the sample size. Here, $n = 67$, so the degrees of freedom are $67 - 1 = 66$.

The Following MINITAB Output Presents a Confidence Interval for a Population