Thursday, December 20, 2007

Teaching: more on graphs and research in intro classes

While I'm on break between semesters, I'm working on revising and improving a new intro class group project that I introduced this past semester. (The lab sections are going to monitor a local stream, similar to what groups like Colorado Riverwatch do. We've got four to six lab sections, and each one will collect data from a different reach of the stream.) I'm especially trying to use this project to help students learn how to understand graphs better.

My experience this semester was mixed. That isn't surprising: a senior thesis student was still collecting baseline data, and a lot of the project was designed on the run. But I was still disappointed with the way the students interpreted their data. Several groups assumed that they could extrapolate data between data points when the data were collected at specific times two months apart. And I wasn't convinced that most of the students understood the numbers they had, or the units things were measured in, or the significance of the values.

So... it's another semester, and I'm revising the exercise. (It's rare that any new exercise works perfectly the first time around, anyway.) We're going to spread the exercise through several weeks (for fifteen minutes or so at the beginning of lab - we aren't going to cut other labs to make room for this one). Here's the basic schedule:

Week 1 - introduce project, use topo maps from field sites for the topographic maps lab

Week 2 - graphing-by-hand exercise, using monthly average discharges for the 2006 water year. This will be complicated because there is a reservoir between two of the sites, so they will graph data upstream and downstream of the reservoir. Hopefully, besides practicing their graphing skills, they will also start thinking about how water is stored and used in the western US.

Week 3 or 4 - use Excel to graph the fall 2007 data collected by the senior thesis student. (There will be a field trip on the other week. We live in the Southwest, and it can be clear and fairly warm, even in January. More field trips! Yay!)

Week 5 - choose groups (discharge, sediment, or one of two water chemistry groups) and write one page of background on the type of data being collected. (What is it, what controls whether it is high or low, why do we care about it.)

Week 6 - write one page (or less) about what they expect (given location of the field site, previously collected data, what they know about the weather at that time of year).

Week 8 - collect data in field.

Week 9 - ICP analysis for one of the water chemistry groups. (I still haven't figured out how to let the students see what the instrument does, without making them spend the entire day in the lab with me.)

Week 10 - enter group data in Excel spreadsheet. (I've thought about using Google docs for this, but most of the students don't currently have gmail accounts. For this semester, I'm going to have the lab professor enter the data as students read it off.)

Week 12 - presentation and discussion of results. (Each group will present their original results, and then we'll discuss what they mean in the context of the other groups' results. I'm going to use Moodle to allow the students to share their powerpoints and graphs with one another.)

Week 14 - final papers on the project due.

I spent a good part of this week reorganizing the data in Excel, in hopes that I could make the entire graphing process simple enough that students could learn anything from it. Now, I know that Real Scientists don't use Excel. (Though, ummm, I do. Not for complex math, but for organizing data and doing simple calculations. It works pretty well for recalculating mineral compositions from microprobe data, and for doing unit conversions, and for calculating stream discharge.) And I also discovered that, ARGH, Excel 2007 has really been reorganized, and I had to relearn everything I had known about making graphs in Excel. (I'm still not sure how to remove the graphs from the data without losing everything... it must be possible to make the graphs static, not dynamic, but I haven't figured out how yet.)

But besides the general frustrations of working with newly updated software, I discovered a few other things that might be pedagogically interesting:

- Excel doesn't really care what units are associated with what data. It will happily (as a default) plot discharge, pH, turbidity, and ppm of Na dissolved in water... all on the same Y axis. It takes a bit of work to choose what to plot against what.

- The easiest X-Y plot to read (scatter connected by lines) helps a reader to keep track of which data points go together, but it suggested a continuity in the data that doesn't really exist.

- On the other hand, Excel recognizes dates, and spaces them with appropriate distances between them. That's nice, because the senior collected data in July, and then went off to work as a river guide for six weeks before coming back to really start work in September.

I'm asking students for examples of situations when they shouldn't plot data on the same graph. One has to do with units. But because I want them to see the changes in each variable through time (or along the length of the river), I also want them to think about whether the changes will be visible if both types of data are plotted on the same graph. (If one element is present at 0.1 ppm levels, and another is present at 100 ppm, then changes in the element with the low concentration are impossible to see.)

I'm also asking the students to look at the graphs and notice (qualitatively) which variables seem to rise and fall together, and which have opposite patterns, and which seem entirely unrelated.

And now, after a lot of cutting and pasting in Excel, I'm wondering: is this going to be enough? Too much? Will they learn anything from this? Will they be bored to tears, or will they see patterns that make them more curious?

Edit: I thought about another issue while I was waking up this morning.

Using Excel requires access to computers. We've got a department computer lab, but it only has four computers. We've got wireless access in the geology labs, but not all students have their own laptops. (Perhaps more do than I am aware. I'll have to ask them at the beginning of the semester.) There are computer classrooms on campus, but they are in high demand, and I don't want to drag the class across campus for a short exercise.

So. If they don't have access to their own laptops, which is more important: having all the students use Excel themselves, or having the instructor available while they work? I could have them work in groups in out computer lab (but then only one person touches the computer), or I could make this a homework assignment (and make them complete it without being able to call me over whenever they got stuck).

Maybe most of the students will have wireless-enable laptops, and we'll be able to work in the classroom. That would be ideal...


Chuck said...

"Now, I know that Real Scientists don't use Excel."

No, but many geochronologists do. And we use it for most of our ICP data reduction.

As for the ICP, it *IS* a black box. NO need to explain the inner workings there- most reasearchers don't know that.

Kim said...

Good - I'm glad to hear that there are uses for Excel. (It does perfectly well with massive amounts of addition, subtraction, multiplication, and division, and I would rather do those things with a spreadsheet than a pocket calculator.)

The inner workings of the ICP *ARE* pretty mysterious. But ours has the capability to go back and look at the spectra around the peak of interest. That's a great feature, and it's made it possible to see exactly why, in some cases, different wavelengths give really different reported concentrations for the same element. And it's a huge A-HA! moment for the students when they see and understand why they're getting reports of negative concentrations.

Karen said...

"Now, I know that Real Scientists don't use Excel."

Utter garbage. I'm a Master's student in geology, and I can't count the number of times a professor has commented, "I used to have to write a script to do this, but Excel handles it well." In my thesis work, I'm using it to sort out all kinds of data relationships, and I've figured out how to make it do ternary diagrams. It's a very cool tool!

Kim said...

To make ternary diagrams? Really? How?

(My intro students aren't going to deal with ternary diagrams, but my senior thesis students do...)

Yami McMoots said...

My old company had an Excel template for ternary diagrams. IIRC, you gimmick up a normal X-Y scatter plot - make the X-Y axes invisible, massage the data to plot in the right place, plus some extra data series for the ternary axes.

It was great, until you needed to do anything different with the template, then it was a confusing black box.