There is a theory, discovered by Todd Davis in 1995, that every stock, ETF, bond, commodity, currency and essentially any financial market follows a predictable 17 day pattern. The concept is basically that the actions and emotions of fear and greed represented by three major type of investors converge to form 17 day patterns. The first type of investor is the long term investor. This investor only trades once or twice a year. The second type of investor is the mid term investor who trades about every four weeks. The third type of investor is the short term investor or day trader.
In Mr. Davis' research for a better stock indicator, something other than the reliance on stock analysts, he looked for common points in time where stocks started their upward trends as well as their down ward trends; basically, where each stock started success or started failure. After years of analysis, a consistently recurring, elemental pattern in any stock, bond, commodity, or any other market traded by people had emerged. The pattern was that every stock cycled in 17 day increments.
Todd Davis' work can be found today at his website – pro17.com