4. GDP-weighted Momentum; 9:30-11:30 wins

Buying stocks that have risen and selling stocks that have dropped, called “Momentum,” is a trading strategy that is almost accepted. Even the strongest efficient market theorists strain to explain it away. The following PDF is a comprehensive recent summary:
 “Fact, Fiction and Momentum Investing” by Clifford S. Asness, etal.

factfiction_momentuminvesting.docx
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My buy-SPY-at-noon-sell–at-close strategy is related to stock momentum but with a key difference. It’s not based on stock follow-thru but on ETF country movement.  The relative size of a country's GDP determines the weight of its ETFs in my model. (Based on many many attempts, predicting SPY based on SPY momentum itself, i.e., stock-like momentum, fails consistently.)
 
The tables below record the opening and closing time of stock markets in the 40 largest countries by GDP in 2016 as reported by the IMF.  I’ve taken some leeway with times. For instance, India and Indonesia open and close an hour or 2 later than China yet I've used China times. While Russia and Turkey open and close an hour or so earlier than EU countries yet I've used EU times..

Region	Percent of World GDP	Countries
Asia	35.2%	China, Japan, India, Korea, Aust, Indonesia +
Europe	30.3%	EU, Russia, Turkey, Switzerland & MiddleEast
US	27.1%	United States
US, AmericasExUS	7.2%	Brazil, Canada, Mexico, Argentina

Time	Regions with Markets Open	Percent of World GDP Trading
4pm - 9pm	None	0
9pm - 4am	Asia	35.2%
4am - 9:30am	Europe	30.3%
9:30 - 1130am	Europe, US, AmericaExUS	64.6%
11:30am - 4pm	US, AmericasExUS	34.3%

​The second table shows 9:30 to 11:30 as the busiest trading hours for stocks related to the largest percent of the world’s GDP. (One might ask why noon in my model rather than 1130 when European markets close? Well earning announcements and Mario Draghi statements, are often released after the close. ) When 65% of the world’s markets trade positive, the US often continues upward although it’s important to note that my model isn’t pure momentum. It depends on relative world stock movement during the news intensive 9:30 to noon period, on volatility during this period, and on premiums and discounts of  non-US ETFs.

It's curious that the US following other world markets reverses the mutual fund problem of the early 2000s where arbitrageurs would buy funds holding foreign stocks at 3:55 when the US market rose in the afternoon. Fair-value pricing, accepted by the SEC in 2003, eliminated this loophole caused because funds were using stale prices (local closing prices of non-US stocks.) The current opportunity doesn't depend on such an institutional inefficiency.