in 07-08 GFC the STI fell i think 50-55% from 3800 level to 1600 level... I dont think this kinda drop comes very often... maybe once in 20 years only
the other drops are the 2011-12 european crisis in which we saw the sti fall 20% from 3300 to 2700 level
and the 2015-16 oil crisis in which we saw the sti fall 30% from 3500 to 2500 level
looking at this 3 events, maybe we can say that a 20-50% correction comes once every 4 years?????
Past trends are not very useful to predict the future nowadays with increased globalization.
I feel the general trend nowadays is funds will flow to where-ever the hot-spot are, rising USD --> US, falling USD --> Gold/JPY/CHF, Stagnant USD --> where got more chance to grow.
IMHO, 07-08 crisis is due to house loan default --> falling of big player --> trigger economic repercussion, i.e. domino effect and big crash.
Euro managed to prevent the fall of Greece in 11-12, hence no domino effect. But there is still a major correction.
15-16 is more akin to bubble burst like dot com, but the big major players can still ride out the storm, hence no domino effect leading to big crash.
Personally, I feel that it is onwards and upwards for the next few years till there is technical correction. But I shall always kept some spare ammo just in case.