This discussion of the paper I'm presenting this week in Macro Group appeared today at Vox EU:
Inflation can be pure
too, by Ricardo Reis and Mark Watson, Vox EU: Everyone seems to care about
inflation. Policymakers worry about controlling it; journalists demand answers
to why it just went up or down; the public rates it in surveys as a major social
problem; and academic economists use measures of inflation as much as any other
number. (Try opening an issue of any general interest economics journal and
count how many articles use a measure of inflation to deflate something.)
Inflation is the rare economic concept that deserves an entry in the dictionary,
which typically goes something like “inflation is the overall increase in
prices.”
A key step in turning this definition into something concrete is choosing how
to add up all the price changes into a single number. The answers to this “price
index” problem have typically fallen into two well-separated groups. One group
studies indices as statistical estimators, and focuses attention on probability
models, sampling uncertainty, and so forth. Another group focuses on the
economic fundamentals behind the index, like consumer or producer behaviour,
economic welfare, or some predicted correlation with key observables. This tight
separation leaves all of these measures exposed to criticism: the first group
for having little to do with economics, the second with typically being too
tightly linked to modeling specifics and details.
There is one measure of inflation, though, in which statistics and economics
meet. And luckily, it is one that is pretty central to economics. In almost all
introductory economics courses, the time comes when the teacher tells the
following story: “Imagine that every price in the economy exogenously doubled.
What used to cost €1 now costs €2, those who were paid €15 per hour now are paid
€30, and what was worth €100 now is worth €200. Crucially, no relative prices
change. Therefore, because people care about trade-offs in making choices, no
one will behave any differently. There is no ‘money illusion’ in that changes in
the unit of account don’t change anything real at all.” Students then hear this
result again, when they take microeconomic theory and learn that demand
functions are homogeneous of degree zero in prices and income, when they take
macroeconomics and learn about long-run vertical Phillips curves, and when they
take history of economic thought and learn about David Hume.
Central to this economic story with its sharp prediction is a measure of
inflation defined by two statistical properties: (i) all prices increase in
exactly the same proportion, and (ii) the change is unrelated to any
relative-price movements. The extent to which (ii) holds is what we might call
the measure’s “purity.” A measure of inflation is purer the more it has been
stripped from relative-price changes and so it is closer to the thought
experiment that economists tell their students.
While authors as far back as David Hume or Francis Edgeworth discussed pure
inflation, the concept went through most of the XXth century without much
notice. The exception is a short and (unfairly) neglected article by Michael
Bryan and Stephen Cecchetti published in 1993. They had the key insight that the
methods of factor analysis are well-suited to extract pure inflation, because
these methods give a straightforward way to measure the common component in
price changes that affects all equiproportionately.
In our own work, we noticed that factor analysis also gave a natural way to
purify the measure of inflation. Factor analysis produces a set of components
(or factors) that explain why prices move together. One of these factors is the
equiproportional change in prices that Bryan and Cecchetti emphasised. But the
other factors are just as interesting. These factors are measures of
relative-price changes due to some common source (say productivity, fiscal, or
monetary shocks), and it turns out that a few of these alone account for a great
deal of the variability of price changes. Therefore, we can use them to
statistically purify our measure of inflation from these main sources of
relative price movements.
When we did this for the United States, we found that most of the movements
in conventional measures of inflation like the Consumer Price Index (CPI), its
core version, or the GDP deflator are due to relative-price changes. Only around
15-20% of the movements in these measures of inflation correspond to pure
inflation. Most of the time, pure inflation and CPI inflation are broadly
related, but there are interesting exceptions. For instance in the late 1990s
and early 2000s, CPI and core inflation were relatively low, but pure inflation
was actually quite high. Favourable relative-price shocks seem to have accounted
for most of what was seen back then as surprisingly low and stable inflation in
spite of loose monetary policy.
With our measure of pure inflation, we can also check the claim that there is
“no money illusion”. Dating back at least to Phillips and his famous curve,
economists have found that measures of inflation are robustly correlated with
measures of real activity. Most theories explain this as a result of relative
price changes. In sticky-price models, for instance, when monetary policymakers
intervene, some firms change their prices while others do not. Because there is
a change in the relative price of the goods sold by these two types of firms,
consumption and production plans change and so quantities change. However, since
economists only have crude measures of relative price changes, this explanation
of the correlation between real activity and inflation has not been directly
tested. A worrying alternative is that, in fact, there is money illusion, and
the story that pervades our teaching of economics is just wrong.
Armed with our measure of relative-price changes and pure inflation, we
re-examined the Phillips correlations. What we found was reassuring. After
controlling for relative price changes, the correlation between inflation (or
pure inflation) and real activity is essentially zero. So, when we see that high
inflation typically comes with low unemployment or high output, this is indeed
driven by the change in relative prices hidden within the inflation measure.
When there is pure inflation, that is when all prices increase in the same
proportion independently from any relative price changes, nothing happens to
quantities. Neoclassical economics seems to have this one right.
References:
Bryan, Michael F. and Stephen G. Cecchetti (1993). “The Consumer Price Index
as a Measure of Inflation.” Federal Reserve Bank of Cleveland Economic Review,
pp. 15-24.
Reis, Ricardo and Mark Watson (2007). “Relative Goods’ Prices and Pure
Inflation” CEPR 6593, December.
http://www.cepr.org/pubs/dps/DP6593.asp