There is little evidence that the size, complexity, and reach of some of today’s SIFIs are necessary in order to realize  3  One such measure is “CoVaR”: The prefix “Co” in front of the conventional abbreviation for value-at-risk is meant to refer to the co-movement of losses for a particular firm with those of the system as a whole.
See Tobias Adrian and Markus K. Brunnermeier (2009), “CoVar.” Federal Reserve Bank of New York Staff Report No. 348. Another is “Marginal Expected Shortfall,” which predicts how much the stock of a specific financial firm will decline in a day relative to an overall market decline. See Viral V. Acharya, Lasse H. Pedersen, Thomas Philippon, and Matthew Richardson (2010). “Measuring Systemic Risk”.