I would like to create a table like this:
| H1 | h2 | <--- is centered vertically
| T1 | |
| T1 | text | text | text |
| T1 | text | text |
| T1 | text |text | text|text |
How can I do so? mainly the problem is with row 2.
Working example but not centering correctly the row with 5 columns
\begin{table}[!hbt]
\centering
\caption{caption} \label{tab:table}
\begin{tabular}{c c c c c c c c c c c c c}
\toprule
xxxxxxx & \multicolumn{12}{c}{yyyyyyyyyyyyyy} \\
\midrule
aaaaaaa & \multicolumn{12}{c}{\multirow{2}{*}{bbbbbbbbbbbbbb}} \\
$E=\lambda \cdot x$ & \multicolumn{12}{c}{} \\
\midrule
cccccccc & \multicolumn{4}{c}{ddddddddddddddddddd} & \multicolumn{4}{c}{eeeeeeeeeeeeeeeee} & \multicolumn{4}{c}{fffffffffffffff} \\
$P=\beta \cdot x$ & \multicolumn{4}{c}{(4)} & \multicolumn{4}{c}{(3)} & \multicolumn{4}{c}{(1)}\\
gggggggggg & \multicolumn{3}{c}{gggggggg} & \multicolumn{3}{c}{ddddddddd} & \multicolumn{3}{c}{ggggggggg} & \multicolumn{3}{c}{dsdsdsds} \\
$I=\gamma \cdot x$ & \multicolumn{3}{c}{(6)} & \multicolumn{3}{c}{(5)} & \multicolumn{3}{c}{(3)} & \multicolumn{3}{c}{(1)} \\
Calidad canal & \multicolumn{4}{c}{aaaaaaaaaaaa} & \multicolumn{4}{c}{hhhhhhhhhhhhhhhhhhhhhh} & \multicolumn{4}{c}{rrrrrrrrrrrrrrrr} \\
$\Delta = \delta \cdot x$ & \multicolumn{4}{c}{(5)} & \multicolumn{4}{c}{(3)} & \multicolumn{4}{c}{(1)} \\
\bottomrule
\end{tabular}
\end{table}
tabularx
; cf. this question.