Purchasing Power Parity

Purchasing power parity states that the price of a good in one country
should equal the price of the same good in another country,
exchanged at the current rate—the law of one price.

There are two versions of the purchasing.

power parity theory:

the absolute version and the relative version.
Under the absolute version,

the exchange rate simply equals the ratio of the two countries' general price levels,
which is the weighted average of all goods produced in a country.

However,
this version works only if it is possible to find two countries,
which produce or consume the same goods.

Moreover,
the absolute version assumes that transportation costs and trade barriers are insignificant.
In reality,

transportation costs are significant and dissimilar around the world.

Trade barriers are still alive and well,
sometimes obvious and sometimes hidden,
and they influence costs and goods distribution.

Finally, this version disregards the importance of brand names.

For example,
cars are chosen not only based on the best price for the same type of car,
but also on the basis of the name ("You are what you drive").