Why blame only media and politicians for the public’s confusion about imports and trade deficits? Surely economists deserve some scorn. Some of the misunderstanding can be traced to the famous National Income Identity, which expresses gross domestic product, as: Y = C + G + I + (X‑M). That is, national output (Y) equals personal consumption (C) plus government spending (G) plus investment (I) plus exports (X) minus imports (M).

The expression clearly lends itself to the wrong interpretation. The minus sign preceding imports suggests a negative relationship with output. It is the reason for the oft-repeated fallacy that imports are a drag on growth. Here’s why that conclusion is wrong.

The expression is an accounting identity, which “accounts” for all of the possible channels for disposing of our national output. That output is either consumed in the private sector, consumed by government, invested by business, or exported. The identity requires subtraction of aggregate imports because consumption, government spending, business investment, and exports all contain, in various amounts, import value. Americans consume domestic and imported products and services, the aggregate of which shows up in Consumption. Likewise, Government purchases include domestic and imported products and services; businesses Invest in domestic and imported machines and inventory; and, eXports often contain some imported intermediate components. Thus, the identity would overstate national output if it didn’t make that adjustment for iMports. After all, imports are not made on U.S. soil with U.S. factors of production, so they shouldn’t be included in an expression of our national output.

To reiterate, it is a simple matter of accounting: as an expression of national output, the National Income Identity subtracts imports only because imports are that portion of consumption, government spending, investment, and exports that are not produced on U.S. soil with U.S. factors of production. If we did not subtract an aggregate import value, then national output would be overstated.

But what unnecessary confusion that identity has created. Economists are often indecipherable, but here was an opportunity to actually connect with the public and describe a relatively easy concept in relatively easy terms. Why has it not been commonplace to use notation that conveys in no uncertain terms that C and G and I and X include some amount of imports? Maybe something like this:

Y=C(d)+C(m)+G(d)+G(m)+I(d)+I(m)+X(d)+X(m)-M,

where (d) connotes domestic; (m) connotes imported; and M=C(m)+G(m)+I(m)+X(m).

Again, imports are subtracted, not because they are a drag on output, but because imports are included in the other constituent elements of the identity. I’ve always found it misleading that the parentheses go around X‑M – which isolates the expression “net exports,” but in the process can obscure the fact that imports are subtracted from the whole expression.

Finally, if the description above makes sense, then you’ll agree that imports have NO impact on national output. Regardless of how large or small, the import value embedded in the four constituent elements of national output is fully deducted by subtracting M. Thus, imports are neither a drag on GDP, nor can they cause GDP to rise. That conclusion may sound like it contradicts one of my assertions in yesterday’s post—that imports are pro-cyclical—(at least that was the claim of a NBER economist responding my post yesterday), but I think the conclusions are harmonious. To say imports are pro-cyclical means that they rise when the economy is growing and fall when the economy is contracting. It says nothing about causation. That pattern has been amply and consistently demonstrated through expansion, recession, and recovery.