Welcome new readers!

The "New to the blog? Start here" page will give you an overview of the blog and point you to some posts you might be interested in. You can also subscribe to receive future posts via RSS, Facebook or Twitter using the links on the right-hand side of the page, or via email by entering your address in the box. Thanks for reading!

Wednesday, October 5, 2011

Supply and demand without the curves?

We discussed supply and demand in my Econ for Teachers class this week. This is usually one of my favorite weeks in this class because we do an in-class double-oral auction, which I don't get to do in principles anymore (since I'm not brave enough to try it with 500 students) - I use Aplia for that class instead and while it's better than not doing it at all, it's just not the same. I love watching the students get into their buyer and seller roles. There is always a few who surprise me, some students that I think of as being relatively quiet but they end up being enthusiastic negotiators. And students always tell me at the end of the semester how memorable the auction is for them.

But as I was preparing the materials for class, it dawned on me that no where in the California content standards, or in the national standards, are supply and demand curves mentioned. That is, standard 12.2.2 of the California standards says, "Discuss the effects of changes in supply and/or demand on the relative scarcity, price, and quantity of particular products" and standard 12.2.5 says "Understand the process by which competition among buyers and sellers determines a market price." National standards 7 and 8 say "(Students will understand) Markets exist when buyers and sellers interact. This interaction determines market prices and thereby allocates scarce goods and services" and "Prices send signals and provide incentives to buyers and sellers. When supply or demand changes, market prices adjust, affecting incentives." On the one hand, it certainly is possible to just talk intuitively about market prices and quantities adjusting to changes in supply and demand, without using a graph of the curves; but on the other hand, it seems like the intuition is so much easier when paired with the visual of the graph. But maybe it just seems that way to me because that's how I've always done it?

Partly, I'm thinking about how difficult it seems to be for students to go from the experiment data (giving the number of buyers with different buyer values and sellers with different seller costs) to graphing the curves. It feels a bit like just a graphing problem because when I go datapoint by datapoint (for example, asking, "At a price of $5, how many sellers will be willing to sell?"), they have no trouble answering and they intuitively understand the relationship between price, buyer value or seller cost, and willingness to buy or sell. But when left to finish drawing the curve, they often get lost again, as if they just can't connect the intuition they understand to the grid in front of them.

So I'm wondering how weird it would be to try to discuss supply and demand and equilibrium price and quantity without the curves. I just don't know if it would 'work'. I'm particularly thinking about student confusion about what I think of as the 'never-ending story' problem: something happens that causes demand/supply to change (shift) and that leads to a change in price, which students then think causes demand/supply to change as they confuse shifting the curve with moving along the curve. Of course, if they actually follow that argument through, that shift should cause price to change again, which causes demand/supply to change again, etc. Since that process could just continue forever (and yet we know it doesn't in reality), there must be a flaw in that argument, and I think the curves can help clarify that flaw. I can't really figure out how I would explain what's wrong with that argument without using the curves. Yet, I think there are a lot of high school economics courses that do not introduce supply and demand curves. Do they just not do supply and demand at all (that would be my own high school experience)? Or are they talking about supply and demand without the curves somehow? If anyone has taught it that way, I'd love to hear from you in the comments!


  1. I really agree with the facts that you have shared on this post. An interesting topic like this really enhances reader's

    mind to have more effective decisions over a certain issue.
    CCTV Karachi

  2. FWIW, common student problems with S&D makes for fertile ground for good conceptest questions.


Comments that contribute to the discussion are always welcome! Please note that spammy comments whose only purpose seems to be to direct traffic to a commercial site will be deleted.