October is remembered for the big historic crashes in 1929 and 1987. It was also a shocker during the GFC in 2008, although things really kicked off with the Lehman Bros collapse in mid-September.
US commentators - who write a lot about the October effect - point out that there were also October falls in 1971, 1977, 1978, 1979 and 2011.
There are almost always plenty of global economic and geopolitical issues for investors to worry about if they want to but for some reason they want to more in October.
Certainly, the last few weeks have seen some worrying issues emerge.
JBWere chief investment officer Bernard Doyle summarises them nicely in his latest market report.
He highlights economic growth concerns out of China and Europe. A German slowdown in particular has shaken confidence. The IMF also downgraded its global growth outlook at the start of the month. Bond yields are falling again and oil prices have plunged - both signs that forward looking investors are less confident.
Then there is Ebola, which Doyle describes as "the true wild card" in the mix. "The history of these health scares [Bird flu, Sars] is they tend to have a short, sharp impact on markets," he says.
But if Ebola were to spread further in an advanced economy like the US then markets would begin to price the economic consequences.
The risky disease is already starting to spook the aviation sector and has potential to cause further disruption to consumer sentiment.
However, even if it starts to have some short-term economic impacts, "Ebola is highly unlikely to shift our medium term portfolio positioning," Doyle concludes.
Overall, Doyle remains confident arguing that the market reaction to recent events has been exaggerated.
In New Zealand, the market held up pretty well until last week. It is now down a little over 4 per cent since it closed on October 1.
Leading the fall last week was our premier tech stock Xero, which probably has a lot of exposure to US investor sentiment. In fact, Xero is now down 21 per cent since the start of October.
That's forcing some analysts to re-evaluate their outlook for the company.
To the credit of Xero chief executive Rod Drury, he never made a big deal of the share price rise last year, when stock was soaring. He has always maintained a steady course with regard to the company's growth strategy and goals. That gives him some real credibility as he sticks to the same story now.
Xero has clearly been caught up in a fair amount of market hype, good and bad, on which Drury is wisely refusing to base his business decisions.
Meanwhile, for both Xero and the wider markets here and the US, there is some upside to pricing falling back more closely into line with real economic growth.
The longer a bull market runs, the more detached from reality it becomes. Then the potential for full-blown investor panic and an economically damaging crash grows.
The giant US economy is still lurching slowly back to life. It remains a security blanket for investors and is keeping serious panic at bay.
Nothing is certain, of course, and certainly not in October.
