Figure 9

Evolution of the average similarity of user profiles. Similarity, as measured by the numbers of common books or groups, and by the cosine similarity, is shown for links created between t and $t+1$, for $t=2$ (black circles), 3 (red squares), 4 (green diamonds), 5 (blue triangles), normalized by the average similarity in the first snapshot. Values are quite stationary before $t_0$, and clear jumps are observed between t and $t+1$.