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Alpha Theory Blog - News and Insights

« June 2022 | Main | August 2022 »

1 posts from July 2022

July 28, 2022

What does it mean to be a good stock picker?

 

Bottom Line Up Front: A batting average above 38% demonstrates stock picking skill for an active manager. 

 

Defining skill in investing is challenging, so it is no surprise that measuring skill is even harder. While we strongly believe there is an inherent skill for many “stock pickers,” how do we measure that belief? What if we compare them to the “blindfolded monkey throwing darts?” (Sidenote: unless monkeys can read, I think the blindfold is superfluous). Said another way, can the manager beat a randomly constructed portfolio? 

 

In this experiment, we will measure skill by measuring two metrics: batting average and slugging percentage (Batting = # of positions that make money / total number of positions | Slugging = average percent gain of winning position/average percent loss of losing position).  

 

Important Note: Demonstrating skill does not mean beating the market. It also does not mean making money. I know, weird. You can be better than the monkey throwing darts and still lose to the market because indices do not equal weight the stocks in the index. 

 

Batting Average 

 

ABSOLUTE BATTING AVERAGE. Let us start by building the comparison portfolio from the ACWI Index (All-Country World Index - ~3000 global stocks - ~70% US). To demonstrate skill, a manager should be able to “beat” random. Over the past five years, the ACWI has had a 56.4% batting average (if you randomly picked 100 stocks from the ACWI, 56 of them had a return greater than 0%).

 

INDEX ADJUSTED BATTING AVERAGE. You could say that during the past five years, a manager should make money on 56% or better of their long positions. The problem with looking at it this way is that some five year periods are more positive than others. A potentially better approach is to measure the number of stocks that beat the ACWI. The ACWI was up +40.9% during this period. Once we subtract that return, only 27.1% of stocks beat the ACWI. To assess, the manager would simply measure the number of stocks up more than the ACWI during the holding period. If that was higher than 27.1%, they were demonstrating skill. 

 

EQUAL WEIGHTED BATTING AVERAGE. The problem is that the last five years have seen the largest returns from the biggest index weights (large caps outperforming the small caps).  To get a random selection of the ACWI (like a monkey throwing darts), we should equal weight the ACWI. Equal weighted, the ACWI is up 21.7%. This more reasonable version results in a batting average of 37.8%. 

 

From this, we would argue that a batting average above 37.8% demonstrates skill. The higher above, the more skill demonstrated. Of course, there is luck involved, and untangling skill and luck is difficult, but over time, we can look for persistence of skill in picking winners and losers with this metric*. 

 

So far, the only skill measured is that of picking stocks that go up. In the next post, we will measure the skill of picking the stocks that go up the most and avoiding those that go down the most (Slugging – position sizing skill).