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AP.MACRO:

MEA‑1 (EU)

, MEA‑1.I (LO)

, MEA‑1.I.1 (EK)

, MEA‑1.I.2 (EK)

Let's say we're studying a
very small and oversimplified country that only
sells apples, and we measure the GDP in year one. And we measure
that GDP as $1,000. And all of that
is due to apples. And we also know that the price
of apples in year one was $0.50 a pound. So I'll write it
as $0.50 per pound. And let's say that now
year one has gone by and even year two has
gone by, and we're able to measure the
GDP in year two. So the GDP in year
two is $1,200. And the price of apples in year
two, let's just say it is $0.55 a pound. So my question to you is, GDP,
the whole point of measuring GDP, is measuring the
productivity of a country. I mean we are measuring
in terms of dollars, but we care more about
just the dollar amount. We really care is, was this
country more productive? And if it was more productive,
how much more productive was it? And if we just look at these
GDP numbers right over here, this $1,000 versus this
$1,200, it gives you the sense that-- well, at least if you
just look at the numbers-- $1,200 is 20%
larger than $1,000. So if you just look at those
numbers right over there, it looks like the
GDP grew by 20%. But is that an
accurate representation of the productivity
of this country? Did it actually
produce 20% more goods? And a big clue is looking
at this price here. Because some of
this GDP actually might have increased
just due to price. But that doesn't actually make
the country more productive. The quantity, the extra
quantity of apples that the country
produces, is actually what adds to the
total productivity. One way to think
about it-- Let me draw a little diagram over here. On this axis, I'll do quantity. On this axis, I will do price. And P1, so if I want to figure
out the GDP in year one, I would have the price
of apples in year one-- that's the only good or service,
just to simplify things-- times the quantity of
apples in year one. And then this right
over here, the area of this green rectangle,
would GDP in year one. And then GDP in year two would
be the price in year two. So we're going to go
from $0.50 to $0.55. The price in year two times
the quantity in year two-- we'll assume some growth as
occurred-- times the quantity in year two. And so GDP in year
two would be the area of this entire rectangle. And if we want to find
the difference between GDP in year two and
GDP in year one, it would be the difference in area. So it would be what I am shading
in, in blue right over here. And based on the numbers that
we went over right over here, the area that I'm
shading in, in blue-- so the difference between GDP
in year two and GDP in year one, the area I'm shading
in blue-- would be this 200, the 200 increment. So this area right over
here would be that 200. Now when you look
at it over here, you see that that
200, some of it is due to an
increase in quantity. But a lot of it is also due
to an increase in price. So if we really wanted to figure
out how much more productive the country got, and we still
want to measure GDP in dollars, maybe we can take
a measure of GDP that measures year two's
GDP, but it does it in year one's prices. So if we could
somehow multiply-- if we could multiply year two's
quantity by year one's prices, then we would get this
rectangle right over here. And then the difference
between that and year one, would give us the incremental
GDP in year one prices due to quantity. And that's what we care about. We care about
total productivity. When we're thinking
about GDP one, we say how much more
productive did the country get? So let's try to do it with
these numbers right over here. So we can figure
out quantity two, we could figure out the
quantity in year two just by dividing the
GDP by the price. Just by dividing this area
of the entire blue rectangle and dividing it by the price,
that will give us the quantity. So if we divide 1,200
divided by $0.55-- let me get my calculator out. So if I do 1,200
divided by $0.55, this is my quantity of apples
and in pounds in year two. And I'll just round it, 2,182. So this is 2,182. So the quantity in year
two is 2,182 pounds. So this is equal to that. And then I could multiply
this times the price. So this is this quantity. It's 2,182 pounds. And then I could multiply it
times the price in year one at year one's price. So I'm going to
multiply it times-- P1 is equal to $0.50 a
pound, $0.50 per pound. And this will give me-- so let
me just get my calculator out. I should be able to do
that one in my head. But let's see 0.5. And I get 1,090. Obviously, I'll
round it to 1,091. So this is equal to 1,091. And this is an
interesting number. So this is-- you could view
this as year two's GDP. In year-- or adjusted for-- I'll
write it, adjusted for prices, or adjusted for price increases. Or you could say
in year one prices. And what's useful about
this is, this says, look, if prices had remained
constant, this is what our GDP
would have gotten to. If prices did not
increase, our GDP would have gotten to this 1,091. 1,091 is this area that
I drew in pink here. And so now, you could say if
prices were held constant, the growth in GDP would
have been $91 not $200. So this area right over
here that I'm-- actually, let me do it in a color. Let me do it in orange, maybe. This area right over
here, the actual growth, if prices were held constant,
would have been $91. We would have gone from
$1,000 of GDP to $1,091. So this right over
here, that area, is $91 of-- and we could
even call it real growth. It really measures
the productivity. Now this gives us an
interesting, I guess, set of ideas. One idea is to just measure
your GDP in the current year's dollars. So this was GDP measured
in year two's dollars. It was year two GDP measured
in year two dollars, year two prices. So we could call that
year two's nominal GDP. Nominal, in name. So it's GDP in name,
in that year's prices. But this right over
here, where we measured year two's GDP, in some
base year's prices-- so it allows a real
comparison of how much did our productivity
actually increase. Our productivity
actually increased by 9%. We produced 9% more apples. This, we call real GDP. Because it gives you a
measure of real productivity. It tries to take
out price increases. What we'll see in the
future, or we might not do it in an introductory
course, but in practice, it's kind of hard
to really measure what the absolute-- this was a
simple economy, where we only had one product. But if you have many, many,
many products-- actually gazillions of products in a
real economy and the prices are adjusting and the
quantities are adjusting, it's not so easy to figure
out how to adjust for price. But the folks running the
national income accounts do try to do this. So they get a sense of how much
was the actual real growth.

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