13.13 Gold prices.
Consider the monthly data on the price of gold ($ per troy ounce) from January 2000 to July 2014.8
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13.13
(a) The Runs Test and the ACF show the price of gold series is not random. (b) The variation of the price changes for gold is increasing with time. (c) These differences approximate the percent change in the price of gold. (d) The first differences of the log price data show much more constant variance than the original differences.