IPS - Day 46

Today we looked at using experimental design. This piece is the third leg of working with sample surveys, observational studies, and experiments.

The experimental investigation comes from "How Fast Do They Melt in Your Mouth?" investigation from NCTM's Navigating through Data Analysis in Grades 9-12 book. I like this investigation because it reinforces vocabulary while allowing students to think about the overall structure of an experiment.

Today the class worked through the first seven questions and then we discussed their responses. Questions concerned treatments, experimental units, response variables, factors that could affect the experiment's outcome, scope of inference, and causality.

This was a good discussion and students had to be tuned into the vocabulary in order to answer the questions. It has been a couple of weeks since we actually discussed experimental design, so there were a lot of questions about the vocabulary.

We then discussed responses as a class. There were some questions about the specifics of the treatments; would milk chocolate and white chocolate chips really fit within the context of the problem statement? How do you capture the melt time?

As always, as we list out factors that could impact the study, I had to be careful to specify the context as such things as open or closed mouth, mouth temperature, amount of saliva, size of piece, and so on take on a whole new context with high school students. I use this as an opportunity to say that context is important because we don't want any misinterpretations of what the experiment is about.

The scope of inference was also an interesting discussion. Some students questioned whether the result is valid beyond the individual or beyond the group being tested. Others wondered if the results might be applicable to others in their grade level or perhaps the entire school. Others thought the results could apply to a much broader group.

For homework, students were asked to design a two-sample and a paired sample design. I briefly described the difference in these designs. The two-sample design consists of two independent groups. Assignment to the groups is random. One group receives on treatment and the other receives the other treatment and then the results from the two groups are compared.

For the paired sample design, there is a direct connection between the pairs. In this scenario, one person receives both types of chocolate and then their melt times are compared.

Tomorrow, the groups will come to a consensus for an experimental design and then we'll discuss designs as a class. The goal is to have the class decide on an experimental design which can be carried out by the class.

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