Dictionary of Evidence-based Medicine.pdf

Dictionary of Evidence-based Medicine 131
freely. Examples of such goods are houses and cars. Quasi-private goods
are similar to private goods except that they are not freely traded in competitive
markets. Examples are public libraries and park amenities (Mitchell
RC, Carson RT (1989) Using surveys to value public goods: the contingent
valuation method. Resources for the Future, Washington DC).
Public interest detailing (see Academic detailing)
Publication bias
The bias which arises when positive results are published while negative
or null results are not (see File drawer problem and Funnel plot).
Purchasing power
The purchasing power of a currency (PPC) is the amount of goods that it
will purchase in its home economy. A conversion rate between currencies
can therefore be based on what one currency unit (e.g. US$) will buy in
its home economy (the USA) and working out how many currency units
(e.g. Yen) would be required in another country (Japan) to buy the same
amount of goods. The US$ is often used as the reference currency unit
for such comparisons. A PPC-based conversion rate is therefore not the
same as the market rate as the former takes account of cost of living in the
different countries. However, a key component of international economic
analysis is the theory of purchasing power parity which says that in the
long run, a US$ should purchase as much in the USA as anywhere else in
the world after adjustment for transportation costs and therefore, in the
long run, changes in exchange rates reflect relative inflation rates. Economic
statistics such as the gross domestic product (GDP) are often
reported in terms of both market rates and PPC.
Use of PPC produces some surprising rankings. For example, in the
World Bank report for 1995, while the USA has the highest world GDP at
both PPC and market exchange rates, China moves from seventh position
based on market exchange rates to second position using PPC. India
similarly moves from 15th position to fifth position. The PPC is often
referred to as the purchasing power parity in the popular literature.