From base price levels of 100 in 1987, West German and U.S. price levels in 1988 stood at 102 and 106, respectively. If the 1987 $/DM exchange rate was $0.54, what should the exchange rate be in 1988? In fact, the exchange rate in 1988 was DM 1 = $0.56. What might account for the discrepancy? (Price levels were measured using the consumer price index.)