The Economist Index

The Economist occasionally publishes a "Big Mac Index" — how much the world's favorite "burger" costs in each country, translated into a common currency.

Why they don't publish an index of how much an issue of the Economist costs?  All of my issues have the price of the newspaper in lots of Asia-Pacific currencies. A small sample:

• Australia, 9.39855 USD


• Cambodia, 6.00 USD


• China, 10.43655 USD


• Hong Kong, 7.6917 USD


• India, 5.0522 USD


• Japan, 10.70535 USD


• New Zealand, 8.6669 USD

Can anyone tell me why the price varies so much?