Back in '08 a model was developed based on inflation. A few interesting things came of it but I found this to be the most intriguing. Using macroeconomic data, & some market return data, this bubble-o-meter of sorts became apparent. Notice the clustering of "crash" events at one extremity of the variable. Now updated for 2009 to 2013 still needs 2014 update. The puzzling thing to me is that in the current environment I keep going back to this thinking "this must be it" & checking this gauge for signs of pending doom... Alas still no such warning flashing. ... Of course it's difficult to cry "causality" ... And we have to acknowledge that the current central bank induced distortions are unprecedented and thus arguably any model grounded in reason can be discarded, as there is no reason in the system.
the markets and trading volumes are generated by banks which are proxies for the government. Almost every market is manipulated to fit the scenario they wish. Take a look at oil prices. The market can only crash when its prudent for the government to crash it. You will see downward blips but prices will resume regression trend upwards.