rescaled time $\tau=130$ with $N=508$ products and the particle density $\rho=400$ detailed in Sec. \[sec:modelb2\]. Inset: The second moment $\langle A^2\rangle = N^{-1} \sum_p A_p(t)^2$ versus $t$. The solid line is obtained by excluding crude oil (3330). (b) Evolution of individual products’ share, denoted by name and 4-digit SITC code. While the share of SITC 3330 and that of 2786 stay mostly contained in the central 80% of simulated trajectories (shaded areas), 2231 and 8996 show large deviations from model predictions detailed in Sec. \[sec:individual\]. (c) Dependence of the annual variation of share $\Delta A_p(t)=A_p(t+1) - A_p(t)$ on $A_p(t)$ in case of both (left) $\Delta A_p>0$ and (right) $\Delta A<0$. []{data-label="fig:empirical"}](Fig1revised.eps){width="\linewidth"}

We analyze the NBER-UN dataset [@feenstra2005world], which contains trade volumes of $N=508$ product types based on the Standard International Trade Classification (SITC Rev. 2) and consistently reported over the period 1962-2000. A single datum $V_{c,c',p}(t)$ is the amount of trade (in nominal dollars) from country $c$ to country $c'$ in product category $p$ in the year $t$. We investigate product share $$A_p(t) = \dfrac{\sum_{c,c'} V_{c,c',p}(t)}{\sum_{c,c',p'} V_{c,c',p'}(t)},
\label{eq:Apt}$$ which is the fraction of the total amount of money involved in trade worldwide that is exchanged with product $p$, and thus 