Option Trading Idea of the Week
Testing a Statistical Rule of Thumb From TerrysTips.com
We have always held the position that we had no idea which way the stock was headed in the short run (but over time, it has gone up about 10% a year, so we should lean a bit in the upside direction). This assumption seems to have served us well over the years.
However, a time-tested rule of thumb in the world of statistics is that for almost any curve of economic activity, the direction of the change in the next period is more than twice as likely to be in the same direction as the direction of the change in the last period. This rule of thumb supposedly applies to all time periods, whether they are daily, weekly, monthly, or annually.
For sure, if you examined a moving average curve for a stock or index, every subsequent change is almost always in the same direction as the last change. Very rarely does the curve hit a bottom or top and reverse direction.
I wondered if we could use this rule of thumb to predict the direction the market might be headed based on what it did in the previous month. If more than twice the time, the change was in the same direction, we could benefit considerably by setting up risk profile graphs which had more room for the stock to move in that particular direction. If this statistical rule of thumb held true, maybe we should change our basic assumptions and the strategy as well.
To check out the idea with SPY, I checked the monthly changes in SPY over the last 10 years. In exactly 60 of the months, the stock moved in the same direction that it had in the previous month. In exactly 60 of the months, it moved in the opposite direction that it had in the previous month. A perfect tie.
The only conclusion that we could make from these numbers is that our original assumption that we just don't know is probably about as good as we are likely to get. The statisticians are not always right when it comes to the real world, at least when it comes to monthly fluctuations of SPY.
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Terry
Overbought/Sold Condition Report
Overbought/Oversold as of October 5, 2009
Major Benchmarks
- S&P 500 (SPY) - 23.1 (neutral)
- Dow Jones (DIA) - 21.5 (neutral)
- Russell 2000 (IWM) - 22.4 (neutral)
- NASDAQ 100 (QQQQ) - 23.1 (neutral)