Gross Domestic Error

Pierre Lemieux at EconLib catches a surprising error from The Economist which wrote this week:

There was some head-scratching this week, as data showed Japan’s economy growing by 2.1% in the first quarter at an annualised rate, defying expectations of a slight contraction. Most of the growth was explained by a huge drop in imports. Because they fell at a faster rate than exports, gdp rose.

Nope. Imports do not influence Gross Domestic Product, at least not in the mechanical way suggested by The Economist. Here’s how Tyler and I explain it in Modern Principles:

It’s important to remember the Domestic in Gross Domestic Product. When we add C+I+G we are adding up all national spending but some of that spending was on imports, goods that were not produced domestically. So we subtract imports from national spending to get national spending on domestically produced goods, C+I+G – Imports.

…Here is a mistake to avoid. The national spending approach to calculating GDP requires a step where we subtract imports but that doesn’t mean that imports are bad for GDP! Let’s consider a simple economy where I, G, and Exports are all zero and C=$100 billion. Our only imports come from a container ship that once a year delivers $10 billion worth of iPhones. Thus when we calculate GDP we add up national spending and subtract $10 billion for the imports, $100-$10=$90 billion. But suppose that this year the container ship sinks before it reaches New York. So this year when we calculate GDP there are no imports to subtract. But GDP doesn’t change! Why not? Remember that part of the $100 billion of national spending was $10 billion spent on iPhones. So this year when we calculate GDP we will calculate $90 billion-$0=$90 billion. GDP doesn’t change and that shouldn’t be surprising since GDP is about domestic production and the sinking of the container ship doesn’t change domestic production.

We continue:

If we want to understand the role of imports (and exports) on GDP and national welfare. We have to go beyond accounting to think about economics. If we permanently stopped all the container ships from delivering iPhones, for example, then domestic producers would start producing more cellphones and that would add to GDP but producing more cellphones would require producing less of other goods. If we were buying cellphones from abroad because producing them abroad requires fewer resources then GDP would actually fall—this is the standard argument for trade that you learned in your microeconomics class. The standard answer could change, however, if there were lots of unemployed resources, an issue we will discuss in Chapter 32 and later chapters. The point we want to emphasize here is not whether trade is ultimately good or bad but rather that Y+C+I+G+NX is an accounting identity that can’t by itself answer this question.


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