and 1987 gets an asterisk because 1987 was an up year despite the crash. By the Dow anyway.
So a 30%+ fall is somewhat rare but it does happen so it has to be one of your factors.
relatedly, apparently there have been only two back to back declines since WW2. 1973-74 and 2001-2002. It is very hard to keep the market down 2 years in a row.
And right now we are down for 2015.