\begin{center}
\begin{tabular}{|ccc|}
\hline
 Sums of squares & Degrees of freedom & Mean sum of squares \\
\hline
 $SS_{Tr}$ & $a - 1$ & $MS_{Tr} = \frac{SS_{Tr}}{a - 1}$\\
\hline
 $SS_E$ & $N - a$ & $MS_E = \frac{SS_E}{N - a}$\\
\hline
\hline
 $SS_T$ & $N - 1$ & \\
\hline
\end{tabular}
\end{center}