Figure 3.

The success of a person's recommendation of a product as function of the number of recommendations that he sent. A person could recommend a product to friends only after he purchased the product himself. The success is measured as a normalized rate of receivers buying the product upon the recommendation. The normalization counts each product purchase equally in terms of the system's dynamics, as follows: if a person receives multiple recommendations for the same product from different senders, a ‘successful purchase’ is only accounted to one of the senders. The grey area is within 1 s.e.m. The total recommendation network consists of four million persons who made 16 million recommendations about half a million products. The subnetworks of the books and DVDs categories are by far the largest and most significant, with 73% of the persons recommending books and 52% of the recommendations concerning DVDs. The data for these plots were kindly provided by Leskovec et al. [39]. (a) DVD, (b) books, (c) music and (d) video.