New York (CNN Business) Some politicians and market participants believe the US dollar is too strong compared to its rivals. Now there's another indicator: Burgers.

The Economist's Big Mac Index -- a lighthearted way to make the value of currencies more tangible -- showed that nearly all currencies in the index are undervalued against the dollar.

The Big Mac Index, released Wednesday, is rooted in the theory of purchasing power parity: Exchange rates reflect the value of goods a currency can buy. If currency X can buy an item at a lower price than currency Y, then currency X may be comparatively undervalued and currency Y could be overvalued.

The dollar's strength isn't new, but over the past six months, it has grown even stronger, the indicator shows.

McDonald's MCD The euro, the dollar's main rival, has fallen further in value against the dollar since the start of the year.Big Mac is now 19% cheaper in the eurozone than in the United States, compared with 17% half a year ago.

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