Based on a quick survey [1], seems like various forms of glucosamine are not interchangeable. Doesn't this confound the study further given its unclear which supplements led to what outcomes?
>> THE BIG MAC index was invented by The Economist in 1986 as a lighthearted guide to whether currencies are at their “correct” level. It is based on the theory of purchasing-power parity (PPP), the notion that in the long run exchange rates should move towards the rate that would equalise the prices of an identical basket of goods and services (in this case, a burger) in any two countries.
Burgernomics was never intended as a precise gauge of currency misalignment, merely a tool to make exchange-rate theory more digestible. Yet the Big Mac index has become a global standard, included in several economic textbooks and the subject of dozens of academic studies. For those who take their fast food more seriously, we also calculate a gourmet version of the index.
[1] https://www.mayoclinic.org/drugs-supplements-glucosamine/art...