Before revision:  and (ii) chain-like, associated with high-volatility economic crisis . When we examined successive corresponding segments within the present housing bubble financial crisis, we find that each MST can be obtained from the one before it through a minimal set of primitive rearrangements, each representing a statistically significant change in the cross correlations of the sectors involved .
After revision:  and (ii) chain-like, associated with high-volatility economic crisis .