I've never seen market valuation expressed as market cap as % of GDP. I'm not an economist, so I'll leave the detailed arguments to them. But it would be at least useful to explain why you think this is a meaningful metric as compared to those typically used to measure market valuation (e.g. P/E ratios etc.). Your graph also ties your valuation metric to the 2000 peak and the 2008 peak. However, there were crashes in…
That this ratio doubled in 8 years is worrisome.
The thing is that an alternative analysis is to look at the linear regression since 1980 and it seems clear that a background upward tendency does seem to exist, so we can see 2009 as an adjustment to the 2008 crisis and 2017 as only slightly above the expected trend.