Currency weakness leading to higher import prices is a hallowed cause-effect connection for economists. But it’s a link that may be eroding.

Exchange rates are a hot topic as the U.S. and China hold their third annual round of the Strategic and Economic Dialogue this week. The link between a weaker dollar and prices is also gaining in importance because the Federal Reserve is coming under fire about inflation pressures in light of rising commodity costs. The Fed says the effect of such cost increases are “transitory.” Businesses and consumers aren’t so sure.

Certainly, import prices have increased as the dollar has weakened. Over the year ended April, the trade-weighted value of the dollar fell about 6%, while the prices of non-oil imports increased 4.3%.

Much of the price gain, however, reflects higher costs for imported commodities and supplies. The prices of imported capital and consumer goods — items that feed more directly into broader U.S. inflation measures — are up only about 1% over the past year.

Economists at the Fed have looked into the link between exchange rate and import prices. What they found is the pass-through effect from a weaker currency eroded from the 1980s into the early 2000s.