[math] \begin{array}{cc} & \text{Sibling} \\ \text{Patient} & \begin{array}{c|c|c} \hline & \text{No tonsillectomy} & \text{Tonsillectomy} \\ \hline\text{No tonsillectomy} & 37 & 7 \\ \hline\text{Tonsillectomy} & 15 & 26 \end{array} \end{array} [/math]