The extent to which a price fluctuates. Fluctuations may be measured on any time-scale, from year-by-year to minute-by-minute. The quantitative measure of volatility of the price in period t − 1 is defined as the standard deviation of the natural logarithm of the ratio of prices in period t and t − 1 (log returns). Price volatility tends to be higher when supply, demand, or both are liable to large random shocks, and when the elasticity of both supply and demand is low. Price volatility tends to be higher for commodities, shares, and exchange rates than for industrial products.