When I first read Greg Mankiw's "Ten Principles of Economics" I thought they were embarrassing. But I really liked the rest of the book, and decided to become a Canadian co-author (along with Ron Kneebone and Ken McKenzie of The University of Calgary). I thought that when teaching I would just skim over the 10 principles quickly to get past them. But I changed my mind. I now spend more time (minutes per page) teaching that first chapter than anything else in the book.
This post is about why I changed my mind, and how I teach them.
Then I go totally off-topic and talk about high school math and political correctness.
It was the very idea of "10 Principles" that put me off initially. It sounds too much like "10 Commandments". Nothing in economics is written in stone; everything has exceptions, and is up for debate. And why precisely 10, for heaven's sake? Why not 9, or 11? I kept thinking of the holy hand-grenade of Antioch: "Three shall be the number thou shall count, and the number thy counting shall be three...". What is it with these magic numbers, like 10, or 3?
But when I came to teach them, right at the beginning of the course, I found myself spending much more time on them than I had planned. And the students seemed receptive, and to learn a lot from them.
I finally realised why they worked when I spent 3 hours in Jamaica (with Carleton colleague and Cuban economy blogger Arch Ritter). We went to a restaurant for lunch while waiting for our connecting flight to Havana. I looked down the very unfamiliar menu, and chose the "tourist platter". The tourist platter had a little bit of everything. Obviously designed for people like me, who were ignorant of Jamaican cuisine and wanted a quick introduction.
Greg Mankiw's 10 principles is the tourist platter of economics.
You can define economics as the study of how societies allocate scarce resources. Or you can define it as the study of human interaction based on methodological individualism, rational choice, and equilibrium. Or you can define economics as what economists do; and the best way to explain to new students what economists do is to give them some examples. The 10 principles are just examples of how we think, not holy commandments. And 10 is just a nice round number.
So I tell the students that the 10 principles are the tourist platter of economics. And I tell them to approach each one with a critical eye. Can you think of exceptions where this principle might not make sense? (Does jerk chicken taste good?) Quite apart from anything else, thinking of possible exceptions makes you understand the principles better. Think of an example where rational people would not think at the margin, because the relevant choice is an all-or-nothing choice.
Now I'm going to go off-topic.
There are three ways to understand economics: words, diagrams, and math. In first year we use all three, but with less emphasis on the math, and we keep the math simple. If we think of words, diagrams, and math as three languages, students need to understand the three languages, but they also need to translate back and forth between the three languages. What does this graph mean in words? What does this equation look like in a graph?
And the biggest problem students have is not with math; it's with translating between words and math. Here's a (to me) shocking example.
I do a very simple model of a Production Possibility Frontier, and explain it in words, math, and graphs, to give them practice (and to explain trade-offs and opportunity costs). 10 acres of land, which can grow either apples or bananas. One acre of land planted with apple trees grows one ton of apples per year, 2 acres grows 2 tons, etc. Translate into math, where A is tons of apples, and La is acres growing apples. A=La.
Then I say "One acre of land produces two tons of bananas per year (and 2 acres produces 4 tons, etc). Is that: Lb=2B; or B=2Lb?" I write it all down, let them think about it for half a minute, with no discussion, then hold a vote. Democratic math.
For the last three years I have done this experiment, about 75% of the students vote for the first (wrong) option. Maybe 10% vote for the second option. I glare at the minority, and ask them if they are really sure about their answer. Some hands drop, and the remaining students with their hands up look uncomfortable, but determined. Then I tell them they are right, and the majority is wrong, and explain why.
This teaches us two things: first about political correctness -- how hard it is to look a fool by dissenting from majority opinion, even when you know you are right; and that something is seriously wrong with the majority of students' understanding of math. They might be able to "do" algebra, and rearrange Lb=2B as B=(1/2)Lb, but they don't have a clue what it means. They can't translate between words and math. Many have difficulty even after I plug in some numbers and show them it's wrong. And algebra doesn't get much simpler than y=2x.
Why? What's going on in high schools?