On the recommendation side, however, it is  \textbf{media} that is the more likely to triggers  clicks upon recommendation, followed by  \textbf{politics} and the local category (\textbf{Berlin}. The two least performing categories are \textbf{business} and \textbf{knowledge},  similar to the least performing  categories in base. So, overall, it seems that the likelihood of triggering clicks by the categories shows a difference when they are in base and recommendation.  In general, the  categories have higher CTRs in recommendation that in base. To gain further insight, we looked at the CTRs of transitions from base category to recommendation category. The aim of this is to find out whether some base categories are more likely to trigger clicks on some recommendation categories. The results are presented in Table \ref{heatmap}.

\begin{table*}

\caption{Transition CTR scores from base categories to recommendation categories.  The row categories represent the categories of base items and the column categories represent the recommendation categories. \label{heatmap}}

  \begin{tabular}{|l|l|l|l|l|l|l|l|l|l|l|l|}

\hline