from Peter Dorman
Listen to this excerpt from his interview with John Cassidy:
Back to the efficient markets hypothesis. You said earlier that it comes out of this episode pretty well. Others say the market may be good at pricing in a relative sense—one stock versus another—but it is very bad at setting absolute prices, the level of the market as a whole. What do you say to that?
People say that. I don’t know what the basis of it is. If they know, they should be rich men. What better way to make money than to know exactly about the absolute level of prices.
He makes this point several other times within a few minutes: we know markets are efficient because they are unpredictable.
But those famous monkeys, who sat at their keyboards for centuries hoping to randomly tap out Hamlet, could just as well be inputting unpredictable asset prices.
How can someone be a world famous financial economist and not know the difference between necessary and sufficient conditions?
Update Cochrane too.
Cassidy has him saying:
What efficient markets says is that prices today contain the available information about the future. Why? Because there’s competition. If you think it’s going to go up tomorrow, you can put your money where your mouth is, and your doing it sends (the price) up today. Efficient markets are not clairvoyant markets. People say, “nobody foresaw saw the market crash.” Well, that’s exactly what an efficient market is—it’s one in which nobody can tell you where it’s going to go. Efficient markets doesn’t say markets will never crash. It certainly doesn’t say markets are clairvoyant. It just says that, at that moment, there are just as many people saying its undervalued as overvalued.
To be filed under “not understanding the difference between necessary and sufficient conditions”.