I found this

We ranked 207 cities worldwide based on a basket of goods and services frequently purchased by expatriates.

https://www.imercer.com/content/cost-of-living.aspx

And from the article on the Guardian:

according to Mercer, which measures the cost of more than 200 items – including housing, transportation, food, clothing, household goods and entertainment

http://www.theguardian.com/cities/2015/aug/26/what-where-is-the-worlds-most-expensive-city