The scoring function may also include delayed effects, to reflect on the time-dependent nature of the relationship between financial returns and attention flows (i.e. current performance as a function of previous visibility & demand). The Spearman’s Rank Correlation is the error measure of choice for the machine learning model, since it is agnostic to the exact values and simply measures the correlation of putting tokens in the same order -- the only assumption is the ability to sort the objects (crypto economies) according to each given attribute (sources of attention).