The Details: For this exercise, we asked the students to calculate their Body Mass Index (BMI) using the CDC's BMI calculator and to submit their score anonymously to Laurel's teaching assistant. The TA put all of the scores in an Excel file and sent them to me. Laurel and I posted the BMI's on Blackboard and asked the students to calculate some summary statistics of the dataset, following our detailed instructions (see handout.doc).

We expected most of the students to simply calculate these statistics by hand, so in the subsequent class, I came in to discuss how they could have performed these calculations in Excel (see Figure 1) (of course, some had already figured that out!).

But I also used the opportunity to talk about how Excel can calculate a confidence interval, and how taking smaller and smaller samples from the population (in this case, the full list of BMI's submitted by the students) produces larger and larger confidence intervals (see dataset.xls, use worksheet tabs at the bottom to navigate). We also discussed how confidence intervals and related inferential statistics are calculated as ways to say something about a population for which we do not have complete data.

The Downloads: handout (.doc), dataset (.xls)

The Goals: From my standpoint, there were a number of pedagogical goals for this exercise. I wanted students:

• To know how to calculate basic summary statistics
• To know how to perform these operations in Excel
• To have some sense of what a confidence interval is when they see one reported in a data table
• To know the relationship between a confidence interval and sample size