The Metric Fallacy

We often hear some proclamation, usually in support of subsidizing some activity, that some activity is desirable because it leads to success (for example: “Education is an investment in the future”).  But this is what I will henceforth call the “Metric Fallacy,” which is a specific form of the “ad hoc ergo propter hoc” fallacy.

The fallacy goes like this:

Some desirable outcome, X, is highly correlated with broad category Y.

Therefore, to achieve X, one should increase Y.

The first statement is true (X and Y are correlated).  The second statement, however, is fallacious.  A practical example will help:

It is true that higher education is correlated with higher levels of income.  According to the College Board, a person with even just some college education earns approximately 13% more than someone with just a high school degree.  Higher levels of education are correlated with higher levels of income.

But it is fallacious to, therefore, say that education itself is the cause here.  We need far more information.  The type of education matters a whole lot more.  A person in theology earns considerably less than a person in chemical engineering.  Ceteris paribus, a doctoral degree in a STEM field will earn a lot more than a doctoral degree in religion.

Thus, the Metric Fallacy is: to increase income, we need to increase education.

We see the Metric Fallacy all over the place and in high-ranking areas (Education and Economic Growth Theory and subsequently foreign investment, just to name a few).  Many government policies are based off this fallacy, including minimum wage, subsidized college loans, foreign aid plans that involve capital donations, and the like.  Indeed, probably the greatest lie I heard as a child was “if you want a good job, you have to go to college.”

My colleague and professor Chris Coyne writes a lot about this in his excellent book “Doing Bad by Doing Good,” and it is the main thesis of Bill Easterly’s book “The Tyranny of Experts.”

The other day, I wrote about discovering prices vs imposing prices.  Discovering prices means that we see what prices emerge from the price system, people acting in response to relative scarcity.  When prices emerge, they provide information.  A person in a profession who earns a high salary means there is a relative scarcity of that profession.  He is indeed made better off by this, but it also signals that we need more of that profession.  Prices allow us to discover this information.  But it is a fallacy to conclude that his higher wage is in some way desirable for anything other than this purpose (eg, the protectionist who might argue if he is made “worse” off because of competition, we all are made worse off).