IPS - Day 30

The focus of today's lesson was on sampling, specifically how do we generate representative samples.

To kick things off, I asked students what characteristics would they like a sample to possess. The class did a nice job considering things like gender, ethnicity, age, income, likes/dislikes, and beliefs. In all, their concern was to get representation of these various groups in their sample.

Now that students were focused on the idea of getting representation, I asked them how to determine who to select for a sample of students from the school. The only restriction placed on the sample was that they needed a sample of between 30 and 160 students. I needed to emphasize that the task was not to create questions they would want to ask students; their task was to decide which students they would select to ask.

With that, the class worked in groups for approximately six minutes on determining what they would do. A couple of groups really struggled with the task. They wanted to come up with extensive selection criteria. I asked them how they would determine which students to ask to go through their screening process. This pushed their thinking but not enough to have them view the situation from a different perspective.

I told students the three big ideas of sampling:

1. Generating a representative sample that reflects the population we are interested in studying
2. Randomizing selection to eliminate or reduce any factors that we might not have considered
3. Creating a sample whose size was not too large

We then looked at the sampling designs that the students created. Five different sampling techniques were written on the board. The results provided examples of stratified sampling, cluster sampling, and multi-stage sampling. I discussed how these illustrated these sampling techniques and the key characteristics of each. I also discussed systematic sampling and simple random sampling.

Students seemed to grasp these ideas. For the last 15 minutes of class, I had students decide on two ways of generating samples. The intent was for students to provide more detail on their sampling plan. As I reviewed their designs, the one theme that reoccurred was randomization. Where does randomizing occur in the design? Although students were thinking implicitly that a classroom or a group would be selected randomly, I wanted them to explicitly describe where the randomization took place in their design.

We'll look at what they came up with next class. 

Visit the class summary for a student's perspective and to view the lesson slides.