k_PPP
This bpost is about PPP and cross-border comparison, based on https://en.wikipedia.org/wiki/Gross_domestic_product#Cross-border_comparison_and_purchasing_power_parity
Intuitively, we compare two countries’ GNI by converting both amounts to USD. This is the standard comparison but ignores regional price differences. For example,
- SG is expensive for car owners than most countries.
- U.S. medical and medical insurance (“services”) costs are higher than most countries. Tristate rent is expensive. Suppose your basket is dominated by rent and medical, then using FX rate to compare U.S. vs SG incomes will ignore the high-cost of the U.S. Suppose your U.S. after-tax income of 120k is 20% higher than SG (S$133k=USD100k). The lightly (i.e. 20%) higher income in the U.S. looks like 20% higher quality_of_life.
There’s an alternative exchange rate .. the ppp-fx. Using ppp-fx, the slightly higher income in the U.S. may translate to lower quality_of_life than the S$133k in SG.
Specifically, if someday ppp-fx of Int$/SGD becomes 1.0, then S$133k salary in Sgp has equal purchasing power to USD 133k in US. It would provide (or buy) you a richer quality_of_life than the USD 120k salary mentioned earlier.
( Naturally, we adjust our “basket” and avoid the locally-expensive products like cars in Sgp and medBx in US. )
Using ppp-fx, the same basket would cost the same amount of Int$ in any country. This sentence sounds concise but is unclear. If you observe real world prices and compute an aggregate “basket price” in local currency, then use ppp-fx to convert the basket price into Int$, then the Int$ basket-price would be identical across all countries. Note Int$ has parity with USD, for some theretocal reason.
https://en.wikipedia.org/wiki/International_dollar and https://data.worldbank.org/indicator/PA.NUS.PPP?locations=SG-US tabulate the latest ppp-fx rate of every currency vs the Int$. Int$/USD = 1.0.
- Int$/RMB = 3.64 meaning Rmb 3640 and USD 1k have equal purchasing power locally.
- Int$/SGD = 0.8 meaning SGD 800 and USD 1k have equal purchasing power locally.
- Int$/MYR= 1.54 meaning MYR 1540(=SGD470) and SGD 800 and USD 1k have equal purchasing power locally. Therefore, Singaporeans go to JB for shopping and entertainment.
PPP theory is all about normalizing regional price differences but PPP is inherently entangled with FX. That’s why I call it ppp-fx.
- lower costs in Greece relative to Denmark (all in eurozone) can’t be resolved using ppp-fx. Similarly, cost difference between Shenzhen vs inland China is not resolved using ppp-fx. Instead, you need cost-of-living index.
- PPP-fx is useful for cross-currency comparisons of two salaries.
- PPP-fx is also useful for GNI comparison
- Don’t use BeyondCompare as a main component of a ppp basket. Such a basket is likely to produce a ppp-fx similar to the FX rate.
- The Big Mac exchange rate is one simple example of ppp-fx. You can find readable illustrations.
— Q: is cost level close between China and Sgp? Evidence suggests yes:
- Int$/RMB = 3.64 meaning Rmb 3640 and USD 1k have equal purchasing power locally.
- Int$/SGD = 0.8 meaning SGD 800 and USD 1k have equal purchasing power locally.
Therefore, SGD 800 and Rmb 3640 both have the purchasing power of USD1k (Rember Rule_1). If I convert SGD 800 to Rmb 4440 (2024 FX rate), I can buy “1.2 baskets” in China, since one basket cost Rmb 3640.
— Q: how does inflation affect ppp
A: inflation erodes purchasing power of every currency.
%%A: I think U.S. inflation doesn’t affect the Int$/USD ppp-fx. Suppose this inflation is stable. If China inlation far exceeds U.S. inflation, then Rmb purchasing power would progressively drop against USD
==== some fundamental but non-trivial concepts
Rule_1: “Purchasing power of 1000 units of a currency” is not a vague concept but a number, and always measured in local market.
It’s safe and realistic to assume a consumer has a USD denominated expense account.
Note the PPP-basket is an international standard basket, and distinct from each government’s CPI basket.
— personal quality_of_life (and national standards of living ) .. depends not only on your income but also the actual cost level. Abstract 🙁 Concrete example: Your after tax income, converted to USD, is identical between Sgp, Beijing, NY and Miami, but the same basket of “products” cost more in NY and less in Sgp. Therefore, your quality_of_life is higher in Sgp.
— Most products have location-specific prices. Beijing and Hebei are different locations.
Commodities like cude oil have no loction-specific prices. However, I’m more interested in consumer goods, which indirectly depend on commodity prices.
If your basket is mostly high-tech products like softwarer gadgets, then there’s no location-specific price. Indeed you can use FX because iPhones, BeyondCompare etc are sold at the same USD price regardless of location.
However, in most people’s “basket”, high-tech products are a small portion. A big component of your basket can have a highly location-specific price.
Services as a type of “product” have location-specific prices. The BigMac is a famous example. Converted to USD, it is expensive in Switzerland and cheaper in SE.Asia.