With the recent drop in the Dow Jones, I wondered about the historical trend. I created a workbook with monthly average data I found on the web. Note that my expertise is in visual analysis, not finance, and this analysis comes from that perspective.
With a semi-log plot you can clearly see a generally linear trend to the data:
In Tableau, I can fit a linear trend line to this data by writing a calculation to convert the month to log(month, 10). As you can clearly see, the partial average for this March is currently touching the trend:
You can also see that the Great Depression dipped significantly below the historical trend before the Dow returned to the trend. That is also true for other smaller movements around the historical trend line. If you took these dips to be a precedent for our current market, my visual guess for the bottom of our current correction would be next September around 3,500 for the Dow Jones:
It might be lower since we were above the trend for a long time. Converting back to the a standard trendline, we get the following view:
Of course, all of this assumes that the political and economic situation today is similar to that of the Great Depression, and that our financial system is similarly architected. All of which could be questioned.