represents the popularity of this product in the global economy. While the total trade volume $V_{\rm all}(t)=\sum_{c,c',p} V_{c,c',p}(t)$ grows exponentially, we are here interested in the investment-strategy shifts among various product categories, which are entirely contained in the dynamics of $A_p(t)$.

Remarkably a small number of products occupy a large fraction of total trade [@mantegna1995scaling]. Crude oil (SITC 3330) is the category with the largest share, retaining close to $10\%$ of all trade for the whole period. By contrast, the share for e.g. the category of slag and similar waste (SITC 2786) never exceeds $10^{-3}$. The general shape of the probability density function of product share $P_t(A) =\sum_p \delta(A_p(t)-A)$ is close to a lognormal function $P_t(A) \sim  A^{-1}\exp\left[-{(\log A-\mu)^2\over 2\sigma^2}   \right]$ as shown in Fig. \[fig:empirical\] (a) or a stretched-exponential function $P_t (A) \sim A^{\beta -1} \exp [-\lambda A^\beta]$ [@doi:10.1137/070710111; @Alstott:2014aa]. Many products’ share exhibits significant variation over time, as in the case of orthopedic appliances (8996) and copra (2231) which display steady growth and decline respectively over orders of magnitude in their shares \[Fig. \[fig:empirical\] (b)\]. We find that the annual variation of the share of an individual product category $\Delta A_p(t) = A_p(t+1)-A_p(t)$, when averaged over gains ($\Delta 