Curve Fitting and Over-optimization
A major stumbling block for many market timers is the phenomenon of curve fitting. This means that a given set of trading rules has been over-optimized to fit the particular dataset for which it has been back-tested. Unfortunately, if the trading rules are over-optimized they often fail to work on future data. Market timers attempt to avoid these difficulties in a number of ways. One is by looking for clusters of parameter values which work particularly well. Another is using out-of-sample data, which ostensibly allows the market timer to see how the system will work on unforeseen data. However, critics charge that once the strategy has been revised to reflect such data it is no longer "out-of-sample".
Read more about this topic: Market Timing
Famous quotes containing the words curve and/or fitting:
“And out again I curve and flow
To join the brimming river,
For men may come and men may go,
But I go on forever.”
—Alfred Tennyson (1809–1892)
“Of all the nations in the world, the United States was built in nobody’s image. It was the land of the unexpected, of unbounded hope, of ideals, of quest for an unknown perfection. It is all the more unfitting that we should offer ourselves in images. And all the more fitting that the images which we make wittingly or unwittingly to sell America to the world should come back to haunt and curse us.”
—Daniel J. Boorstin (b. 1914)