Stocks -- fooled by randomness?
I chanced upon an interesting idea/concept while reading a book on risk, titled "Against the gods, the remarkable story on risk", by Peter L. Bernstein.
If the results of an activity is truly random, taking statistical measurements of repeated trials should resemble a normal distribution, i.e. a bell curve. The sum total of two dice repeated sufficient number of times will result in a bell curve with more counts centered about 7 and 8, tapered towards the extreme of 2 and 12.
Does that occur to stocks? With the help of my friend, I got hold of the daily closing value of STI from April 1985 to Oct 2007. I plotted the total counts of daily changes in percentage against the changes and got the following graph.
On first look, the graph fit a bell curve quite nicely. But on closer look, other than the change from 0 to 0.5%, there are more counts for almost all corresponding percentage changes in the positive category compared to the negative ones. e.g. there are more counts of 0.5 to 1% compared to -0.5 to -1% etc.
Daily changes of STI index can be said to be nearly random but skewed towards more positive changes. Hence, over time, STI should appreciate. A check on STI index from 1985 to 2007 verifies this.
In other words, if a typical investor blindly dollar averages STI index (e.g. via index ETF) from 1985 to present, he would have reaped sizable returns while being saved from daily emotional stress, swinging between extremes of anguish and euphoria.
One reason why STI index (or any broad based index of any country with open economy) demonstrates daily randomness is because world events, be it fundamental or sentimental, occurs in random and unpredictable manner. STI is thus affected unpredictably, resulting in short term random behavior. But as the economy of any country with open economy increases over time, so does the index which reflects its economic growth.
Labels: My Thoughts on Investment