IPS - Day 35

This lesson focused on the fundamental differences between observational studies and experiments, which are the last two methods we will study for gathering data.

To begin, the class was asked what comes to mind when they hear the term observational study. Students thought about watching without interacting, looking for details, and being an objective third party. This basically gets to the essence of an observational study. In an observational study choices are not assigned and the observer simply sees what has happened in the past or what unfolds before them as they observe.

I briefly reviewed the ideas of a retrospective study and a prospective study, providing simple examples to help clarify their meaning. A retrospective study involves looking through existing data to accumulate data. A prospective study looks at what happens in an ongoing basis.

In contrast to observational studies, a researcher could conduct an experiment. Experiments are characterized by

1. the manipulation of treatments that are administered to subjects or experimental units, 
2. the random assignment of groups to different treatments, and
3. the comparison of results between treatment groups.

I checked students' understanding by providing three simple examples and asking them whether each was an observational study or an experiment and if an observation study whether the study was a prospective or retrospective study. This helped as many students thought the examples were all experiments. As we discussed these I asked students to focus on whether or not a treatment was being manipulated by the researcher. Using this criteria, students then were able to correctly classify each example.

I asked students to define what an observational study and an experiment would look like if we were interested in studying soup preferences. Students worked in their groups on these and then we discussed. The class seemed comfortable with the idea of how to structure an observational study. They were not as sure about structuring an experiment. I again asked students to consider how to manipulate treatments and how to include random assignment. As this was the first look at experiments, I wasn't concerned that a workable structure was identified, only that the key aspects were being considered.

After this, I provided four more examples for students to consider. In this go around students did a much better job differentiating between an experiment and an observational study.

I started a video on observational studies and experiments. I wanted the class to see an actual observational study in action. The Against All Odds videos, while somewhat dated in look, still provide a solid presentation of the topics. For this particular class I used Video 12: Experimental Design.

We'll finish the video and take a closer look at the structure of experiments and ethical issues surrounding experiments next class.

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