13.43 OPEC basket prices.
In 2005, OPEC introduced a basket price which is the average price of seven blends from different OPEC countries. OPEC uses the basket price to monitor world oil market conditions. Consider data on the daily basket price from the beginning of January 2012 to the middle of August 2014.25
opec
13.43
(a) There is no consistent trend or seasonal pattern, but there are short runs where the value rises and falls. (b) The ACF shows the first differences of the price series are not random. (c) The first differences in a random walk are random; because the first differences for price are not random, it is unlikely the price series behaves like a random walk.