Gold’s Random Walk

A number of journalists are helping to broadcast Goldman Sachs’ latest prediction for gold prices. Goldman’s press agents planted the story in the Wall Street Journal, the Financial Times and the New York Times, among other places.

This is silly. There’s plenty of scientific evidence that the gold price is a random walk. Here’s an old reference: Eduardo Schwartz’s Presidential Address to the American Finance Association back in 1996. There are older and more recent papers finding the same.

Last week I wrote a post in which I mentioned that the time series of commodity spot prices are often mean reverting. They contain an element of predictability. Gold, however, is the exception. Gold is very, very, very cheap to store. And it is widely held purely as a store of value without any use value. Consequently, the spot price of gold quickly incorporates changing market views about future supply availability and any other fundamentals like those itemized in the Goldman report. For all intents and purposes, a physical investment in gold is a financial security, which means that the spot price is a martingale. The distinction I made in my last post between the spot price series for a commodity and the time series for a specific futures price is a meaningless distinction for gold.

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