> Right, but what is the purpose of statistics like this? The purpose is for them to inform our understanding of what might happen in the future. As mentioned above, since market movements follow a power law rather than normal distribution, the average gives us absolutely no information about what might happen. Thus this statistic fails at the goal of having a purpose; it is just a meaningless number, like those meme baseball statistics about who is the third-best thrower of fastballs on a rainy friday or whatever.

Thanks for restating using almost the same words and using an apparently non-applicable analogy (i.e., the 42% covers all bursts effect on indexes, your sports example covers individual performance). My experience is people who provide such poor explanations usually don't actually know what they are talking about.

Your claim on its usefulness makes assumptions about where to apply the information. The perma-bears use these kinds of numbers to demonstrate why being in stocks during a bubble is a bad idea.