This comes from a new working paper by David Yermack titled “Is Bitcoin a Real Currency?”
Yermack looks at the historical trading behaviour of Bitcoin and compares it other currencies. What he finds is that bitcoin is incredibly volatile and its exchange rate movements have no correlation with other currencies. The virtual currency’s inherent stability makes it impossible to use it as a store of value. For this reason, Yermack concludes that bitcoin looks more like a speculative vehicle than a real currency.
The following chart shows bitcoin’s volatility compared to four other fiat currencies and gold: