Were you able to view the PBS link. Has anyone viewed the article? It somewhat addresses the Purchasing Power Parity comparison as to what a local family buys and compares their relative lifestyles and what their currency buys for their typical daily food and products.
Interesting, s your Economist links to the article states:
"Thus a Big Mac in China costs 10.5 yuan, against an average price in four American cities of $3.10 (see the first column of the table). To make the two prices equal would require an exchange rate of 3.39 yuan to the dollar, compared with a market rate of 8.03. In other words, the yuan is 58% “undervalued” against the dollar. To put it another way, converted into dollars at market rates the Chinese burger is the cheapest in the table."
Further shedding more light on the issue in the article on Big Mac Burger index:
"The index was never intended to be a precise predictor of currency movements, simply a take-away guide to whether currencies are at their “correct” long-run level. Curiously, however, burgernomics has an impressive record in predicting exchange rates: currencies that show up as overvalued often tend to weaken in later years. But you must always remember the Big Mac’s limitations. Burgers cannot sensibly be traded across borders and prices are distorted by differences in taxes and the cost of non-tradable inputs, such as rents."