IPS - Day 45

Today we took a look at observational studies and their claims. I used the "What's This Study Do?" investigation from NCTM's Navigating through Data Analysis in Grades 9-12 book.

This investigation asks students to read through three brief articles centered around cell phone usage and cancer. The investigation asks students to consider the following questions for each study:

1. What is the question of interest?
2. What problems might impact the study?
3. Does the study support the conclusions made?
4. Are the results of the study applicable to all people?

I had students answer these questions individually. They then discussed their responses in their groups. I then had students share out and we discussed their answers as a class. This turned into a thoughtful discussion.

For the first study, students debated whether the question of interest was "Does cell phone usage cause cancer?" or "Is there a difference in cell phone usage between people with and without brain cancer?" After discussion, the class concluded the later was a more appropriate question of interest. Although there wasn't as much discussion around the questions of interest for the other two studies, there were comments that helped to sharpen the focus of the questions.

For problems that might impact the study, the ideas were far ranging and appropriate. There were considerations about bias, random sample selection, cause and effect. I was pleased to see the points brought up were all of a statistical nature.

One point that was brought up was on the difference in sample sizes for a couple of studies. Students tend to believe that when comparing two groups that you must have the exact same sample sizes. We discussed this issue at length. I referred students back to our discussions of what constitutes a representative sample. The sample size deals with the level of precision that we can measure but within the needs of the level of precision we seek, the samples themselves can be different sizes. Students took this at face value but seemed uncomfortable with the idea. I'll need to build in an investigation that will make this idea more real and understandable for them.

Most students did not feel the first two studies, which were observational studies, supported the claims. There was more debate as to the third study, which was an experiment on rats. This was another good debate on the merits of the two types of studies. It also allowed me to revisit experimental design and what conclusions can be drawn from a randomized, comparative experiment.

The class then briefly discussed some ideas they had on the studies. One person brought up the idea that the experiment should be conducted on humans to be conclusive. This allowed us to revisit the ethics of experiments. Another student brought up the idea that cell phones from different eras could possible have different impacts on cancer development. They came up with an idea to include two cell phone treatments in the rat experiment, one that corresponded to older cell phone design and one that corresponded to newer cell phone design.

Overall, the discussion clearly showed students were attuned to the issues and we thinking about the questions from a statistical perspective.

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