Let’s explore a recent, important example of an observational study.
In March 2020, COVID-19 was declared a pandemic by the World Health Organization. In December 2020, vaccines using Messenger RNA technology were given emergency use authorization by the Food and Drug Administration in the United States. Over the next 13 weeks, 3,950 health care personnel, first responders, and other essential and frontline workers who had received the vaccine completed weekly COVID-19 testing to determine whether they had tested positive for COVID-19. In this study, researchers were following the effectiveness of the vaccines in a real-world setting.
For more information about this study, visit https://www.cdc.gov/mmwr/volumes/70/wr/mm7013e3.htm.
Work in groups or pairs to answer Questions 2 – 6.
question 3
Identify at least one potentially confounding variable in this study.
question 4
What are some differences between an experimental study and an observational study?
You may wish to make some notes for yourself if you haven’t already about the key differences between experiments and observational studies.
As you answer Questions 5 and 6, recall the definition of a confounding variable: Remember the definition of a confounding variable: a variable that was not accounted for in a study and may actually influence other variables in a study.
question 5
A PhD student collects data at a local elementary school. For each student, she records their age, grade, height, weight, shoe size, GPA, and score on a state-wide reading test for elementary school-aged children.
Part A: Is this an experimental or observational study?
Part B: The PhD student observes that students with larger shoe sizes tend to score higher on the state-wide reading test. She concludes that having bigger feet improves reading ability. Can you explain why her reasoning is likely to be incorrect? Can you think of another explanation for the higher test scores?
question 6
A study finds that people living in high-density urban areas develop fatal lung cancer at lower rates than people living in low-density rural areas.
Part A: Is this an experimental or observational study?
Part B: A student reads this study and determines that living near many people prevents cancer. Can you think of other things that might explain why low-density areas see higher rates of lung cancer?
Guidance
[Wrap-up: You’ve seen that experimental studies have treatments, random assignment of participants, cause-and-effect relationships, and controls. Observation studies on the other hand do not have different treatments, they do not randomly assign participants to treatments, and they have a lack of control (or knowledge) of confounding variables. You may wish to keep a list of these differences handy until you develop a deep understanding of the difference between experiments and observational studies. ]
