Relevance of data

The key is that we are dealing with uncertainty rather than with risk: even with an abundance of financial data, the dynamics of financial markets are such that only a small proportion of the available data may actually be relevant to the current economic conditions. And, when relevant data are sparse, the variance term tends to dominate the bias term and thus increase the overall prediction error of complex models.

HANSJÖRG NETH and GERD GIGERENZER